An announcing system in which the time, temperature, and commercial weather message announcements are provided on a single mechanism with one record and the TTA system will operate in any spatial orientation including a horizontal position. A stepping motor is used for a magnetic detent of the recording system and operates to positively position the magnetic sound heat in the center of a magnetic record track. Completely automatic time and temperature services are provided with no daily maintenance or initial time setting to maintain accuracy by utilization of the National Bureau of Standard's WWV Radio broadcasts.

Current U.S. Class:	379/71 ; 360/12; 369/22
Current International Class:	H04M 3/487 (20060101); G11b 021/08 (); G11b 019/00 (); G11b 027/10 ()
Field of Search:	179/1.1C,6TA,1.2S,1.2MD,6C 360/12

Watson, Cole, Grindle & Watson

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Claims

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What is claimed is:

1. Time-temperature and message announcing apparatus, comprising:

means for independently storing hour, minute, seconds, temperature and message data;

means for selectively retrieving each of said hour, minute, seconds, temperature and message data;

means for independently positioning each of said means for retrieving in selected portions of said hour, minute, seconds and temperature data, respectively;

means for receiving hour, minute, and seconds update signals and including means for receiving coded radio signals accurately representing time, means for converting said coded radio signals into respective hour, minute, and seconds codes, logic means responsive to said hour, minute, and seconds codes for generating respective hour, minute, and seconds update signals;

means for receiving temperature data from a location remote from said apparatus; and

means controlling the position of said means for retrieving said hour, minute, and seconds data in response to said hour, minute, and seconds update signals and for controlling the position of said means for retrieving said temperature data in response to said temperature data signals.

2. Apparatus as in claim 1 further comprising means for automatically resetting said means for independently positioning to account for a change from standard time to daylight savings time and from daylight savings time to standard time.

3. Time-temperature and message announcing apparatus as in claim 1 wherein said means for independently storing hour, minute, seconds, temperature and message data is a single recording mechanism.

4. Time-temperature and message announcing apparatus as in claim 1 wherein said means for controlling operates automatically in response to said hour, minute and seconds update signals.

5. Apparatus as in claim 1 further comprising means for generating said temperature data and including means for measuring the temperature, a servo system rotated in accordance with the temperature measurement at said remote location and means for converting said measured temperature into binary coded signals, said means including an encoder wheel driven by said servo system and a number of light emitting diodes and a corresponding number of phototransistors aligned on respective sides of said encoder wheel, said encoder wheel including a modified Gray code having bits spaced to compensate for the non-linear readings from said means for measuring temperature.

6. Apparatus as in claim 5 wherein said temperature data is transmitted from said means for measuring the temperature via a pair of telephone lines.

7. Apparatus as in claim 1 wherein each of said means for independently positioning further includes encoder means for each of said means for retrieving and each said encoder means having an encoder plate, a set of light emitting diodes mounted on one side of said encoder plate and a set of corresponding phototransistors mounted on the opposite side of said encoder plate and aligned with said set of photodiodes, and means for receiving the signals from each of said set of phototransistors to generate a positioning signal.

8. Apparatus as in claim 7 wherein said means for selectively retrieving comprises separate modular carriage assemblies for said hour, minute, seconds and temperature data, each of said carriage module assemblies including a pair of spaced slide rods mounted between a pair of mounting plates, a threaded rod extending between said mounting plates and said slide rods, a ball and screw mechanism engaging with said threaded rod, a sound head carriage mounted to slide on said slide rod and engaging said ball and screw mechanism, a step motor for rotating said threaded rod and a positioning member comprising said encoder plate, said photodiodes and said phototransistors.

9. Apparatus as in claim 7 wherein each of said means for independently positioning further includes a step motor responsive to that positioning signal from a respective one of said hour, minute, seconds and temperature encoder means.

10. Apparatus as in claim 1 further comprising means for rotating said means for independently storing and including a rotatable drum having a recording surface;

means for generating stable oscillation pulses for driving said means for rotating;

means for generating period synchronization signals in accordance with the rotation of said drum;

means for generating precise repetitive signals from said hour, minute, and seconds update signals;

means for synchronizing the rotation of said drum with said hour, minute, and seconds update signals, means for comparing said repetitive signals and said stable oscillation pulses to determine whether the rotation of said drum is slow, fast or accurate, and programmable divider means responsive to said fast, slow or accurate comparison signals for adjusting the division of said stable repetitive oscillation signal; and

means for generating pulses responsive to said programmable divider means to control said means for rotating.

11. Apparatus as in claim 10 wherein said means for generating periodic synchronization signals includes a second photodiode and a second phototransistor mounted in sapced aligned relationship with respect to one another and to the housing of said apparatus, a projection extending from said drum and positioned to rotate with said drum between said spaced photodiodes and phototransistors to periodically interrupt the light path therebetween with each revolution of said drum.

12. Apparatus as in claim 10 further comprising means for lubricating the surface of said drum.

13. Apparatus as in claim 10 wherein said means for rotating includes a central shaft supporting said drum, a motor for rotating said shaft, first and second flywheels, a first compliance filter member for mounting said first flywheel to said shaft, and a second compliance member for mounting said second flywheel to said shaft for maintaining the smooth rotation of said drum.

14. Apparatus as in claim 13 wherein said motor is submerged in a fluid to provide viscous damping, cooling and lubrication of said motor.

15. Apparatus as in claim 1 wherein said means for selectively retrieving includes at least three independent channels and further comprising means for generating voice synthesizing signals, and means responsive to said voice synthesizing signals for generating channel selection control signals whereby a different combined message including said hour, minute, seconds, temperature and message date is periodically generated.

16. Apparatus as in claim 15 wherein said means for selectively retrieving further includes means for automatically advancing said hour and minute data a predetermined interval prior to the announcement of each new hour and minute.

17. Apparatus as in claim 15 wherein said means for selectively retrieving includes hour, minute, seconds, temperature and message analog gates respectively controlled by said synthesis signals for generating voice signals respectively from said means for selectively retrieving.

18. Apparatus as in claim 17 wherein each of said analog gates includes a preamplifier and a means for gating the output of said preamplifier in accordance with said voice synthesizing signals.

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Description

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This invention relates to time-temperature-announcing machines (TTA) of the type which will automatically announce the time, temperature, and a commercial message in response to a request made by dialing the central office of a telephone exchange system. Prior art TTA systems have required separate records for the time, temperature, and the commercial messages to be announced and have used gravity actuated magnetic sound head devices and mechanical detent bars for positioning the magnetic sound head at the respective recordings. Such TTA systems are mechanically complex, require a great deal of operator attention, and can be operated only in a horizontal position, thereby significantly limiting the scope of their applications.

The TTA system of this invention presents a significant improvement and advancement over prior art TTA systems and has the following advantages and features over such known systems. The time, temperature, and commercial weather message announcements are provided on a single mechanism with one record and the TTA system will operate in any spatial orientation including a horizontal position. Therefore, the system can be used in spacecraft or in aircraft, etc.

A stepping motor is used for the magnetic detent of the recording system and operates in conjunction with a production ball screw to positively position the magnetic sound head exactly in the center of a magnetic record track, thereby eliminating complex and difficult-to-manufacture detent bars and mechanical linkage. A four magnetic head system enables the machine to be adapted for computer speech synthesis and to provide multiple outputs. Completely automatic time and temperature services are provided with no daily maintenance or initial time setting to maintain an accuracy of 5 milliseconds at all times by utilization of the National Bureau of Standard's WWV Radio broadcasts.

Temperature update data is transmitted to the TTA system at a central location from a remote temperature sensor over a single pair of telephone wires. The accuracy is sufficient for official Weather Bureau temperature certification (plus or minus 1/2.degree. F.) over a 161.degree. temperature range with excellent long term calibration stability. Digital outputs are provided for use in commercial time-temperature outdoor advertising signs as well as inside premise displays. Binary data representing time, temperature are also braodcast over the telephone company's central office dial tone generator to all of its area subscribers for automatically setting digital clocks and other equipment operated from a digital input. This information is received automatically when a subscriber originates a telephone call.

Special circuit enables daylight savings time changes to be preset up to 24 hours in advance of the 2:00 A.M. Sunday morning correction, therefore making it unnecessary for operating personnel to be present when the automatic change occurs.

Continuous variable cycle recordings are made by stepping the magnetic head from track to track in sequence thereby providing up to 21 minutes of recording time with no noticeable interruption as the machine steps from track to track.

The TTA system uses dual compliance flutter filters with the rotating masses and the main drive motor completely submerged in transmission oil to provide viscous damping, cooling and lubrication, thereby enabling production of gear driven announcement machines to be consistently constructed with wide band flutter of less than 0.05 percent.

Automatic weather announcements programmed by ESSA teletype circuits are transmitted with an address and specific forecast for the involved zone in any one of one thousand prerecorded announcement combinations. The local official temperature is included from the Weather Bureau office and after the weather update from ESSA the teletype circuit is seized and the local temperature derived from the local weather office is transmitted back to the Weather Bureau's regional office thereby providing confirmation that the system has actually been updated within any given zone. This provides a "hands-off" automatic service for small communities that is broadcast over the community telephone system. Such a service and its coding arrangement has been described in ESSA Bulletin W-1132, July 18, 1969.

Recordings of locally variable cycle weather announcements made by Weather Bureau personnel from their local office or other remote location, along with the official temperature, are provided over one line telephone circuit to the TTA equipment located in the telephone company's central office. The announcements are distributed over the weather network on a multiple entry demand basis and such a service has application for medium and large sized cities.

In large metropolitan areas, such as New York City where a message rate telephone service is used, the telephone company may lease the time network to distribute sports announcements, such as baseball, football, basketball scores.

An absolute linear encoder fabricated from a metal plate provides feedback as to the exact positioning of a sound head on a magnetic track. The encoder is coded in a special eight-bit gray code and when used for temperature indication provides a range of -99.degree. to +155.degree. F. for a 256 eight-bit code. The encoder is positioned by a resistance bridge to provide an exact code output that corresponds with the temperature to an accuracy of plus or minus 1/2.degree. F.

The TTA system is free from mechanical indexing disturbances caused by record rotation. A greater flexibility of the types of announcement services is provided by the fact that all timekeeping and other functions are external to the TTA mechanism itself. The carriage assemblies are completely modular and are interchangeable simply by unplugging and removing a few mounting screws.

An advance index system is provided whereby the TTA system will advance the hour and minute recordings 6 seconds before the new hour and minute so that the time announcement is completed at the start of the 960 Hz tone marker indicating exactly the beginning of a new hour. The system may also be programmed to advance the hour and minute index for commercial systems where the time is announced in one minute increments.

A synchronizing system is required to bring the prerecorded time announcing record into exact synchronization with the time and this is accomplished on start-up of the TTA system by an optical interrupter switch which is mounted so that the record operates it once per revolution. An internal system counter set by the output of the interrupter switch and another counter is set once every minute by the radio corrected master clock. The outputs of these two counters are compared with each other to advance the main drive motor when the record is slow in relation to the actual time, or retard the main drive motor when the record is fast in relation to the actual time. The accuracy of the synchronizing system is plus or minus 2.4 milliseconds.

A message assembly announcement synthesizing unit provides a message -- hours, minutes, seconds and the temperature -- in sequence on any one of three or more output channels, and central office line trunk control pulses as well. The output of the three or more channels is offset by 5 seconds. the outputs of each of the three channels are exactly the same except for their time relationship or change in temperature. The telephone central office trunks are switched at the next available announcement when a new call comes in by standard central office techniques to improve the quality of the service by limiting the waiting time to a maximum of 5 seconds to obtain access to an announcement. The average waiting time is 21/2 seconds which provides the subscribers with a full and complete announcement even during heavy traffic periods.

OBJECTS OF THE INVENTION

A primary object of the invention is to provide a more economical and less mechanically complex time, temperature, and message announcement system.

A further object of the invention is to provide a significant improvement in reliability and utility of such TTA systems.

A third object is to provide a TTA system which can be applied to computer speech synthesis configurations.

A fourth object of the invention is to provide a time, temperature, and message announcement system which is completely automatic and requires no operator attention.

A fifth object of the invention is to provide control outputs in a TTA system for operating outdoor or indoor advertisiing displays.

A sixth object is to provide a TTA system which may be broadcast over telephone company central office dial tone generator equipment to all area subscribers and which will automatically set digital clocks and other machinery.

A seventh object of the invention is to provide a TTA system that may be automatically set for Daylight Savings time changes.

An eighth object of the invention is to provide a TTA system having continuous variable cycle recordings which are made available by sequentially stepping a magnetic head from track-to-track.

A ninth object of the invention is to provide a TTA system having substantial improvement in flutter performance which is capable of being produced with a wide band flutter of less than 0.05 percent.

A tenth object of the invention is to provide automatic weather announcements selected from any one of a thousand prerecorded announcement combinations and which is programmed by ESSA teletype circuits.

An eleventh object of the invention is to provide a TTA system using an absolute linear encoder to provide feedback as to the exact position of a sound head with respect to a miltiple track recording system.

A twelfth object of the invention is to provide a TTA machine in which all time-keeping, temperature, and weather functions are external to the machine itself, thereby reducing or eliminating mechanical indexing disturbances.

A thirteenth object of the invention is to provide a TTA system having modular carriage assemblies for improving the flexibility of the apparatus.

A fourteenth object of the invention is to provide an improved TTA system having an advance index system for completing announcements at the start of a 960 Hz tone marker at the beginning of each new minute and hour.

A fifteenth object of the invention is to provide a synchronizing system for synchronizing the prerecorded time announcing record with the exact time.

A final object of the invention is to provide a TTA machine having a message assembly announcement synthesizing unit for sequentially generating three or more output channels of messages comprising hours, minutes, seconds, temperature, and a weather/commercial announcement, wherein the average access time to an announcement is considerably reduced over prior art mechanisms.

GENERAL DESCRIPTION

The automatic time-temperature-annoucing TTA system receives a radio signal from WWV via a radio antenna located at the telephone company location. The entire TTA system operates from batteries and power is applied when the system is first made operational. The WWV signal is applied to a standard superheterodyne receiver tuned to the signal frequency. When a sufficient signal input is available, the audio output contains various information including a 100 Hz tone that is modulated with the digital time information. A 100 Hz filter separates the one pulse per second, one frame per minute, information from the other data. This AC signal voltage is rectified and filtered and the fluctuating DC voltage is then applied to the input of a Schmitt trigger. The output of the Schmitt trigger represents the serial binary coded decimal (BCD) official time code that was transmitted originally from WWV. An enable signal is generated by application of a complete time frame of the interrange instrumentation group -- format H (IRIG-H) modified time code -- with the proper identification logic by means of a shift register. The IRIG-H time code has a 1 minute time frame and a 23-bit BCD code word with one minute resolution. The basic element rate is 1 pps. The code is defined in Document 104-70 published by Secretariat, Range Commanders Council, White Sands Missile Range, New Mexico, 88002. The enable signal certifies that the time code is correct, complete and that the received binary coded decimal (BCD) Greenwich mean time (GMT) hour and minute are in the proper position in the shift register. The actual time of the operation of the enable circuitry is 29 seconds after the hour and minute stored in the shift register plus the propagation delay time from the WWV antenna to the output of the radio receiver at the telephone company.

The enable signal is applied to a local presettable clock. Simultaneously, the time is parallelly inserted from the GMT time stored in the shift register subsequent to its BCD-to-binary conversion. The second is generated locally at the 29th second in a minute. A divider chain between a free wheeling 3.9 MHz oscillator and a 1 Hz output is reset so that the next seconds pulse is corrected for the radio propagation delay. For example, a 3 millisecond delay indicates that the next output of the seconds pulse will be 997 milliseconds later. The logic reset delay is adjusted according to the receiver location in the above manner. The local binary block is thereby set to correct GMT time and will remain so as long as an occasional WWV reset is applied. The local free-wheeling oscillator has a drift rate of only five parts in 10.sup.-.sup.8 per day. In the event, for whatever reason, that the WWV signal is unavailable, the local GMT clock may be manually set. A mechanical counter is provided for recording the number of enable pulses per day.

The GMT binary hour is applied to adjustable logic circuitry for subtracting the GMT offset from the local 24 -hour time. For example, 19:31 GMT is equivalent to 14:31 Eastern Standard Time during the winter months when there is a 5 hour offset. During the summer months for daylight savings time 19:31 GMT is equivalent to 15:31 Eastern Standard Time, which represents a 4 hour offset. The normalization to local time is accomplished by operation of a key on the TTA equipment any time within the 24 hours preceding an actual time change. The correction is made automatically at 2:00 a.m. the following morning.

The binary 24-hour time is applied to the TTA hour step motor servo-amplifier and also to a remote equipment shift register, when a 24-hour local clock is desired, or for other special requirements.

The 24-hour local binary time is normally converted by suitable logic circuitry to 12-hour local time and applied to an hour step motor servo-amplifier having a Nixie readout that may be switched from GMT to 24-hour local time, another monitor position indicating the last-received data from WWV, or 12-hour local time. Nixie readouts are also provided for minute and second monitors.

The binary minute output from the presettable local clock is applied to a minute step motor servo-amplifier and a remote equipment shift register. The binary seconds output from the presettable clock is applied to a temporary storage register which is enabled by the presettable clock every 5 or 10 seconds as may be required. The output of the temporary storage register is then applied to a seconds step motor servo-amplifier.

The binary step motor servo-amplifier consists of an 8-digit logic comparator that compares the incoming binary code with the 8-bit binary code derived from the 8-bit modified Gray code converter. The 8-bit modified Gray code is derived from a mechanical metal and coded plate and an LED/photo transistor optical encoder. The metal encoder plate is mounted on the step motor servo-carriage assembly. The step motor is stepped one step at a time at a rate of 60 steps per second in a direction controlled by the logic comparator. The step motor moves the encoder in one direction until the exact code is reached whenever the logic input is larger than the mechanical position of the encoder. However, if the mechanical position of the encoder is lower than the required input, the step motor moves the mechanical encoder in the opposite direction until the exact code is reached. An advantage of the step motor drive is that it is energized when it rests and will remain in the exact position until the input logic code is changed. Additionally, the step motor will return to a given position in the event it is mechanically forced away and then released. Such apparatus represents an absolute encoder system whereby the exact carriage position is defined by the optical encoder and the binary input at all times.

A combination record, playback and erase magnetic head is mounted on the step motor carriage. The exact position of the magnetic head relative to the record is determined by a magnetic detent in the step motor, and adjustment of a ball lead screw nut mechanism, the position of the optical encoder and the input logic code. The ball screw and magnetic detent determine exact head position relative to a magnetic record track and the optical encoder determines which of 256 track positions the head is at for a given logic input. All step motor servo assemblies are alike and are modular and thereby interchangeable.

All time-keeping, temperature measuring, and variable message cycle links are generated by logic circuits and the data is converted into binary codes which the step motor servo-systems match with the proper recording track. The message assembly logic circuitry switches the magnetic head outputs to synthesize the required speech continuity and output. The message assembly unit also generates pulses for controlling the telephone central office common trunk equipment, for example, such as CO and CT pulses. The message assembly master timer is controlled by an optical interrupter switch associated with the record, thereby generating a pulse once per revolution. The message assembly unit blocks any servo changes during the time the track is announcing a message.

The remote equipment register is parallelly set by the local time and official temperature logic. A logic clock transmits a serial output once per second and that data operates a telephone line driver for transmission of digital information to a sponsor's remote location. Audio information is also transmitted over the same telephone wires on a time-sharing basis. The serial output is used at the sponsor's premises for correct time and official temperature displays and, for example, electric outdoor advertising signs. The remote equipment shift register may also transmit digital information to a special telephone company dial tone generator to enable all subscribers within the telephone company's operating area to automatically set digital clocks on their premises. The digital time information may also be used internally by the telephone company in any number of applications.

The entire TTA system is adequately guarded by alarms for notifying telephone central office maintenance personnel in the event of a malfunction of the equipment. The alarm system also functions to "make busy" subscriber trunk circuits.

Telephone trunk circuits previously used in TTA systems usually comprise a relay for indicating connection of an incoming call to a trunk. A holding relay is set to delay the connection of the audio and the "ring trip" of the central office equipment until the beginning of the next complete announcement cycle which is indicated by a CT pulse from the system. A CT relay is actuated for connecting the audio until the end of the announcement cycle and the CT relay is released by a CO pulse from the system to restore the trunk for the reception of a new telephone call. Such telephone trunk circuits have a number of disadvantages and the TTA system of this invention provides a new interface between the TTA system and the telephone central office equipment to overcome such disadvantages and to provide the following advantages. The reduction of the subscriber waiting time for access to the equipment is reduced by 66 percent thereby enabling a longer announcement with the same telephone circuit holding time. A number of mechanical contacts and relays are eliminated by solid state components which also improves the reliability and speed of operation. A further novel and advantageous feature is the use of optical coupling and isolation between the TTA system and the telephone central office equipment.

THE TTA TEMPERATURE DETECTION SYSTEM

The temperature detection system uses a nickel or platinum resistance thermometer, a reference measuring bridge, a servo-amplifier and gear reducer servo motor, and a precision potentiometer as a mechanical feedback position indicator. Such a system has proven reliability wherein a 20 year calibration stability of plus or minus 1/2.degree. F. over the entire 161 degree range is obtained. The servo motor rotates a special optical encoder wheel upon which is etched an 8-bit modified Gray code. The Gray code is a minimum change code that changes only one bit at a time and the non-linearity of the 60 Hz bridge circuit and the resistance thermometer is compensated by the uneven spacing of the Gray code bit combinations on the encoder wheel. Special logic circuitry is provided for the inversion of the two most significant bits in the conversion from Gray code to natural binary code. The temperature monitor parallelly converts a binary code to a Nixie readout. Both positive and negative values of temperature are provided by assigning a positive binary number to 0.degree. F.

The parallel output of the mechanical analog-to-digital temperature converter is encoded by conventional digital logic into a 10-bit shift register. The shift register is driven by a logic clock having a one second output at one minute intervals. The output of the shift register is transmitted to the TTA apparatus at the telephone company's central office via a telephone tone operated line driver circuit. The thermometer and A/D converter, as well as the necessary logic circuitry, are battery powered. A battery charger may be provided for continuous service. The thermometer sensor may be remotely located from its associated equipment by as much as one thousand feet.

GMT CONVERSION TO LOCAL 24-HOUR TIME

The conversion of GMT time to local 24-hour time is accomplished by adding the 24-hour complementary number representing the GMT latitude time zone offset for the local time to the GMT hour. Logic circuits change the 5-bit code representing the GMT to the 5-bit complementary zone offset number which is added to the GMT hour as long as the sum is less than 24; and such summation is performed by an adder circuit. When the sum exceeds 23, an additional binary 8 is added to the total which is entered in every 6th and nonexistent bit. The remaining 5-bit code represents the 24-hour local time.

DAYLIGHT SAVINGS TIME PRESET

Logic circuitry enables the TTA system to automatically provide the necessary time offset from GMT time for offsets such as Daylight Savings Time. This is accomplished by the setting of a switch to either daylight or regular time positions. The switch may be set within the 24 hours preceding the time change, and causes the TTA hour servo system to move the hour sound head to the appropriate track in accordance with the setting of the daylight/regular time switch. A memory latch holds the Nixie hour monitor until the hour which the time change takes place. The binary signal is added to the 24-hour local clock output to account for daylight savings time.

24-TO-12 HOUR LOCAL TIME CONVERSION

Logic conversion circuitry detects the zero hour and adds a binary 12 to the 5-bit hour code. The hours 1 to 12 are unchanged and the hours 13 to 23 are detected and a binary 20 is added to the 5-bit hour code and entered as a sixth and non-existent bit. The remaining 5 bits represents afternoon and evening hours until 11. A format switch enables the output to be changed to either 12 or 24-hour clock format by inhibiting the logic code detector circuitry. The TTA system includes both 12 and 24-hour recordings thereby enabling the clock formats to be instantly changed. The hour advance index logic is also corrected by operation of the formats so as to provide proper operation.

FREE-WHEELING OSCILLATOR AND RECORD POSITION SYNCHRONIZATION SYSTEM

The TTA system uses a free-wheeling crystal oscillator having five parts in 10.sup.-.sup.8 per day stability. The frequency of the oscillator is selected so that its fundamental or harmonics do not interfere with the reception of the WWV signal and also so that the frequency is a binary multiple of 60 Hz. The output of the oscillator is divided to provide suitable logic control signals as well as control signals for operating the main drive motor signal for synthesizing combinations of three channel announcement outputs, as well as signals for operating a master preset clock divider with circuitry for operating the seconds servo system. Periodical control pulses derived from the radio set master clock are used to reset counter and logic circuitry and also to control the main drive motor for advancing or slowing the record.

THE THREE CHANNEL MESSAGE ASSEMBLY UNIT

The message assembly unit provides outputs comprising a complete message, namely the hour, minutes, seconds; 960 Hz tone; present temperature; and a cut-off pulse. A new complete announcement may be provided every 5 seconds or at any integral number thereof. The audio outputs of the sound heads mounted on the TTA machine carriages are amplified when applied to analog amplifiers controlled by the logic signals. Each of the audio gates used to assemble a channel's message is connected to a low pass audio filter and to the audio power amplifier for providing an output suitable for multiple standard telephone subscriber line connecting trunks. A cutoff pulse is supplied to the trunk circuits at the end of each complete announcement cycle. The cutoff pulse also serves as a cutthrough pulse for the next announcement to the telephone subscriber.

An incoming telephone call is switched by standard central office techniques to the first available complete announcement. The incoming call will be required to wait no longer than five seconds with a 2 and 1/2 second average waiting time. The trunk holding time is thereby reduced to one-half of that time required by a single channel system. This results in an advantage over previous systems by providing a full announcement at all times to all subscribers, even during heavy traffic.

The digital logic signals controlling the audio gates in the proper sequence are derived from the record position interrupter switch and the radio set master clock and divider circuitry. An enable output is generated by a message assembly unit to actuate each of the servo systems only at those times when it is permissible to move the respective sound head without interrupting any of the three composite announcements. An hour and minute advance index is controlled by the radio set master clock and the message assembly unit.

THE TTA DIGITAL STEP MOTOR SERVO AMPLIFIER

Servo amplifier circuitry compares an 8-bit natural binary number with an 8-bit modified Gray code generated by the LED-phototransistor optical encoder that is mechanically linked to the servo step motor. THe output of the digital comparator determines the direction of rotation of the step motor to re-position the encoder plate to match the binary input number. The step motor moves the encoder plate as rapidly as possible until the correct position for the binary input number is reached and stops the encoder plate at this point without overstepping. Current applied to adjacent step motor coils provides a magnetic detent for maintaining the encoder plate in its precise position. A display indicates if the input binary code number is equal, less than, or more than the encoder position.

THe linear encoder plate is attached to the carriage assembly upon which are mounted the magnetic sound heads. The detector circuitry for the optical encoder includes a phototransistor and 8 series-connected infrared light emitting diodes mounted opposite the phototransistors. The carriage may be mechanically positioned to any of the 256 tracks on the magnetic record by the ball screw and nut assembly that is connected to the servo step motor. Rotation of the step motor by 90.degree. moves the carriage and the encoder plate exactly by one 8-bit code number as well as the sound head by one record track. The encoder plate is mounted between the 8 light-emitting diodes and the phototransistors thereby providing an 8-bit output that is connected to the servo amplifier input terminals. An 8-bit Gray code is used for the optical encoder because it provides greater mechanical tolerance than that corresponding to an 8-bit natural binary code. The Gray code changes only 1 bit at a time for each of the 256 numbers whereas a natural binary code changes all 8-bits at once on any one number thereby making precise mechanical alignment extremely difficult. A logic encoder circuit converts the Gray code to natural binary code and the 8-bit natural binary output thereof is supplied to two 4-bit digital comparators. The binary number in the input of the servo amplifier represents one of the desired 256 track positions for the location of the magnetic sound head. This 8-bit natural binary code is applied to other inputs of the two 4-bit digital comparators and the output of the comparators provides control signals for driving the servo motor in either one of four positions or for maintaining the servo motor at a given position.

Additional logic circuitry operates an up/down position counter and also generates a signal for initiating operation of the logic clock for generating pulses to step the step motor. The up/down position counter is driven by the digital comparator.

TEMPERATURE AND 8-BIT NATURAL BINARY NUMBER DECODER AND INDICATOR READOUT

This sub-component converts the 8-bit natural binary code into a binary coded decimal code. A mode control enables the indicated output to display either the binary coded decimal code or the temperature.

ADVANCE INDEX OF HOUR/MINUTE SERVOS

The TTA system master clock operates exactly on time as it is set by signals from WWV and therefore in order to obtain correct voice announcements, the apparatus must advance the hour and minute one announcement period prior to the actual time change. Logic circuitry is provided for the 12-hour clock to detect a certain time and add a specified binary number to the 5-bit hour binary number. This advances the servo amplifier's input code to the next hour and the servo system changes the hour sound head's track position to that hour upon occurrence of the hour enable pulse which occurs at the preset time for the actual time of the new hour. The "1" hour is announced in advance of the 960 Hz tone that begins precisely at the start of hour "1". All other hours have a binary 1 added during the predetermined period of the announcement of the hour.

Additional logic circuitry associated with the 24-hour clock is actuated at a predetermined time before hour "24" and adds a given binary number to the 5-bit binary hour code. This changes the hour servo amplifiers input code to "0" hours and the servo system changes the hour sound head's track position to "0" hours upon occurrence of the enable pulse at a preset time before the actual time of the "0" hour. The "0" hour is also announced in advance of the 960 Hz tone that begins precisely at the start of the hour "0". All other hours have a binary "1" added during the reset period before the start of the associated hour.

Logic circuitry is provided for detecting any given time interval before any given hour to alter the binary code at the input of the minute servo to "0" minutes thereby causing the minute servo system to change the minute sound head to the "0" record track on occurrence of the minute enable pulse at a preset time before the new hour. For all other minutes but the first minute, the minute announcement is heard prior to the 960 Hz marker tone.

The seconds announcements change 12 times each minute, that is, once for each announcement cycle and therefore no logic correction is required. Recording of the seconds on announcements are all advanced by one increment.

A set of holding latches provide memory for the servo systems and movement of the servo systems only occurs when a new binary code is applied to the latch input plus the enable pulse from the message assembly unit.

THE TEMPERATURE, TIME AND ANNOUNCEMENT RECORDINGS

The recording medium is a synthetic rubber band cemented to the exterior surface of an aluminum drum and consists of a mixture of cobalt, iron oxide and Hypalon rubber. Silicone oil is used to lubricate the surface of the recording to prevent wear of the magnetic heads and is applied by a felt spreader over the entire length of the record. The original recordings consist of 256 magnetic recording tracks which extend around the circumference of the record. The temperature recordings comprise 160 tracks beginning at one end of the record; the first track indicating minus 40.degree.F. and extending to plus 120.degree.F. Then follow the hour tracks, the minute tracks, and the second tracks respectively, 24, 60 and 24 in number. Five-second increments are used and commercial messages may be recorded in place of seconds in some applications as desired. Whenever a separate commercial record is employed, it is mounted above the time-temperature record and scanned by a separate message readout head attached to the seconds carriage. The commercial message record is approximately 1 inch wide and is used so that the whole time-temperature record will not have to be replaced whenever a commercial message change is required. The rotational speed fo the record is preferably 12 RPM.

Provision may be made for continuous recordings by providing a step at the end of the first track to the end of the next track, which is accomplished in 4 milliseconds. A change of tracks is not audible because the record playback head is precisely timed to the record rotation by the interrupter switch that operates once per record rotation. All 256 tracks may be recorded in this manner. Audio blanking is required while the magnetic head returns from the last track used to the first track. The maximum recording times are 21.3 minutes for 12 RPM and 10.6 minutes for 24 RPM. Control circuitry may be provided to enable variable cycle recordings to be made on any number of the tracks, which control circuitry counts the number of record rotations during recording and a presettable program counter operates on playback until the programmed number of revolutions has been reached. The playback head is then reset to the beginning of the record. The cycle repeats itself until a new recording is made. It is apparent that with proper interval timing, all of the playback heads may be used on the same recording to provide "demand" outputs for better trunk usage.

A casing is provided for the mounting drive motor, worm and worm gear, bearing and the four or more step motor assemblies. The casing is filled with transmission oil to cover the step motors to provide viscous damping, cooling, and lubrication for all the parts therein. The step motors are mounted on a modular carriage support along with a drive screw that advances 0.125 inches per revolution. The magnetic head assembly and the metal optical encoder plate are also mounted to the carriage assembly. The LED optical encoder is mounted to a support member and the visual scale for the encoder is mounted to another support member. The entire carriage assembly is modularly constructed and designed for easier mechanical assembly to the housing of the system. The system may be mounted in a cabinet on ball bearings to enable easy inspection or adjustment of its components.

APPLICATIONS OF THE TTA SYSTEM

The TTA system provides continuous high-quality and maintenance-free central telephone office operation. The system is flexible to provide top quality announcements during heavy-duty service and is modularly constructed to reduce its cost of manufacture.

The system provides precise hour, minute, second and a 960 Hz tone marker that is within 5 milliseconds of the actual time. There is no manual time setting required. The one second "step" correction occasionally made by the National Bureau of Standards is automatically adjusted. The system operates completely independently of utility power lines thereby eliminating a major source of interruption. Daylight Savings Time changes may be preset within 24 hours of the correction and such correction is made automatically when the actual time change occurs.

Special service announcements, whether of national or local interest, or emergency public service announcements, may be interspersed alternately with the time and temperature announcements and then distributed over the telephone company's time announcement network. The system operates with FAA or other operational tape recorders that require continuous accurate time and day of the year recordings. For this purpose, GMT or local time may be provided. Audible and digital recordings may simultaneously be made on one channel of the operational tape recorder for future reference, which information is also broadcast for aircraft flight recorder usage on a VHF radio channel. The system is capable of being carried aboard aircraft when required and other service information such as an aircraft audible voice alarm or instructions to pilots may be provided. It will be readily apparent that the system can be modified for use by police and fire departments who desire such services.

Radio broadcasts, such as the NBS-WWV transmissions for time, day of the year, and warning services, may be automatic or teletyped by programming and thereby requiring no local recording. Commercial standard broadcasting and FM broadcasting of the time and official temperature may be distributed to the general public by using the TTA system.

Time, or time-temperature announcements for telephone company public service are provided and digital time information may also be distributed from the central office and dial tone generated to every subscriber in the operating area for up-to-date special digital clocks requiring such updating. Some of these units may be located in the telephone itself. The digital output information from the TTA system may also be used locally at the telephone operating locations for timing operator-placed long distance calls as well as regular wall clock service.

Variable length locally recorded weather announcement along with the present temperature are obtained from the local weather bureau office and such information is broadcast over the telephone company's weather network from the TTA equipment located in the central office. Time or time-temperature announcements along with commercial announcements are provided for telephone company distribution over the central office time network.

Digital and audio information may be transmitted over a single pair of wires for use by a sponsor to control remote display in electric outdoor advertising signs at remote locations. Thus, accurate time and official temperature and weather announcements are available at remote locations from the location of the TTA equipment.

Multiple composite announcements may be provided simultaneously from the message assembly unit at five second intervals which reduces telephone holding time at the beginning of the announcement and enables better trunk usage thereby providing more economical service. The TTA equipment also provides the telephone company's prerecorded intercept, Number 911, and dial tone first services to its subscribers on a network basis.

Locally recorded variable cycle announcements up to 21 minutes in length may be made with four or more demand readouts that are provided to minimize trunk holding time and such service has application for heavy duty telephone distribution trunk networks.

Automatic weather services with prerecorded announcements programmed by the standard weather bureau code that is transmitted by ESSA teletype circuits for the specific area or zone is provided with the local official weather bureau temperatures. This represents a "hands-off" operation for small communities.

The TTA systm may also be used in computer speech synthesis that normally provides 256 or more words or phrases with four or more readout heads that have access to all tracks to provide state-of-the-art composite announcements. The optical encoders provide absolute head position information to the computer so that natural speech synthesis may be developed from the prerecorded tracks at the lowest possible cost. Such services may be used to provide bank balances, telephone confirmation services, stock market reports, department store sales information, and horoscope forecasts.

Any periodic variable that is measured and can be converted into a binary code may be synthesized and transmitted over an ordinary telephone line in plain language by the TTA system.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a block diagram of the radio receiver, code detector, binary output and enable pulse circuitry;

FIG. 2 is a block diagram of the remote temperature sensor, measuring system and analog-to-digital converter for remote weather bureau indications;

FIG. 3 is a block diagram of the clock, temperature, remote equipment output, dial tone generator, and step servo amplifier circuitry;

FIG. 4 is a block diagram showing the free-wheeling oscillator, divider networks, record synchronization system and the three channel sequential message synthesizer for time and temperature;

FIG. 5 is a combined block and circuit schematic illustrating the programmable divider for changing the rotational speed of the record drum;

FIG. 6 is a combined block and circuit schematic diagram showing the voice synthesizer counter/decoder circuitry;

FIG. 7 is a further block diagram and circuit schematic diagram of the three channel composite voice message synthesizer;

FIG. 8 is a combined block diagram and circuit schematic of the step motor digital amplifier circuitry;

FIG. 9 illustrates in combined block diagram and schematic format the temperature readout circuitry;

FIG. 10 shows the hour/minute advance index and latching logic circuitry;

FIG. 11 is a cross-sectional elevation view of the drive motor and recording housing showing the mechanical components of the system;

FIG. 12 is a top view of the record hub and read head assembly;

FIG. 13 is a detail view of the drive motor and gear drive assembly;

FIG. 14 illustrates an exemplary embodiment of an encoder plate used in the temperature step motor position feedback circuit;

FIG. 15A illustrates the interrupter switch which is mounted on the record drum to provide a reference on the drum for the record drum synchronization circuitry;

FIG. 15B shows an element of the interrupter switch;

FIG. 16 illustrates the optically coupled multiple input connector trunk circuit;

FIG. 17 shows the six input analog gate and power amplifier circuitry;

FIG. 18 shows the five preamplifiers for the five magnetic heads; and

FIG. 19 shows an embodiment of an optical linear amplifier circuity.

DETAILED DESCRIPTION OF THE TTA SYSTEM

The reception and detection of the National Bureau of Standards code from WWV is provided by the circuitry illustrated in FIG. 1. The radio signal from WWV is received by radio antenna 20 at the location of the TTA equipment, which may be, for example, at a telephone company central switching office. The received signal from antenna 20 is fed to a standard superheterodyne receiver 22 which is tuned to the WWV signal frequency. Channel selector switch 24 enables a selected one of a number of frequencies to be switched to audio and signal level monitor 26 and time code detector filters 28. The various frequencies that are contained in the WWV signal are modulated with the digital time information of that signal, thereby requiring time code detection and filters for separating the information. A 100 Hz filter within time code detector and filter circuit 28 separates the one pulse per second, one frame per minute, digital time information from the other information. The output of time code detector and filter circuit 28 is applied to the input of Schmitt trigger 30, the output of which represents the serial binary coded decimal (BCD) digital time code that was transmitted originally from the National Bureau of Standards. That output is a 29-bit serial BCD time code. The time code transmitted from WWV is presently known as the IRIG-H modified time code, and when a complete time frame of that time code has been applied to the input of 30-bit shift register 32, code format detector 34 generates an enable signal that certifies that the time code is correct, complete, and that the received BCD GMT hour and minute information are in the proper position in the shift register. The enable pulse is shaped by shaper circuit 36 and provided as output 37 for use in the TTA system as will be further described hereinafter. The enable pulse is a 20 .mu.second pulse which occurs 29 seconds after the hour and minute stored in shift register 32 including the propagation delay time from the WWV antenna to the output of the radio receiver at the telephone company. The enable signal is fed to WWV update counter 38 via amplifier 40. Clock counter 38 counts the enable pulses which may occur up to 1440 times daily.

The correction for the propagation delay time will be described hereinafter with respect to the components illustrated in FIG. 2. Continuing with FIG. 1, shift register 32 converts the serial BCD time code input into GMT 6-bit BCD hour output 33, 7-bit BCD minute output 35 and 17-bit output for code detector 34. The 6-bit hour output 33 is fed to GMT BCD-to-binary converter 42 which generates a GMT 5-bit hour binary code 43. The 7-bit BCD minute output 35 is fed to minute BCD-to-binary code converter 44 which generates 6-bit minute binary code output 45.

With respect to FIG. 3, the enable signal 37 is applied to the local presettable clock comprising binary GMT 24-hour clock 50, binary minute clock 52 and binary seconds clock 54. The coded time data is parallelly inserted from the GMT time stored in shift register 32 after its code conversion by binary converters 42, 44 (FIG. 1). Hour clock 50, minute clock 52 and seconds clock 54 are each manually settable by hour manual set circuit 56, minute manual set circuit 58 and seconds manual set circuit 60, respectively. Manual set circuits 56, 58 and 60 enable manual setting of the local clock circuitry should the WWV signal be unavailable for whatever reason. The output of binary seconds clock 54 is a one pulse per minute signal which is fed to binary minute clock 52, the output of which is a one pulse per hour signal and is fed to binary hour clock 50. The second is generated locally as the 29 second of each minute by 29th second encoder 62.

The output from binary hour clock 50 is applied to adjustable logic circuitry in order to subtract the GMT offset from the local 24 hour time. For example, 19:31 GMT is equal to 14:31 Eastern Standard Time during winter months which represents a 5 hour offset and the same GMT same is equal to 15:31 EST during the summer months in which daylight savings time is in effect. The GMT to local 24-hour time offset is obtained from offset logic circuit 64, the output of which is fed to daylight savings time preset circuit 66. The daylight savings time's offset is actuated by operating a key in the TTA equipment any time within the 24 hours preceding the actual time change. The correction for daylight savings time will be automatically made at 2 a.m. the following morning.

During winter months, EST is offset from GMT by minus 5 hours and during the summer months, when daylight savings time is in effect, that offset is minus 4 hours. Time change always occurs on Sunday morning at 2 a.m. local time all over the United States time zones (with proper correction for the GMT latitude offset). The TTA system of this invention is constructed so that no central telephone office personnel are required to be in attendance at the time the daylight savings time change is made. The logic circuitry required within daylight savings time preset circuit 66 is as follows. A switch having "daylight" and "regular" time positions is switched to the daylight position any time within 24 hours prior to the tim change. When set to the daylight position, a high level logic output is entered into an AND gate. At 0.1:59:52 to 02:00:00 as determined by the local 24 hour clock circuit 68, a set pulse is applied to the AND gate and the output thereof is applied to the "set" input of a daylight flip-flop. A millisecond reset pulse is also available to the daylight flip-flop to first reset it in the event the switch had been changed to regular time. This reset pulse is provided every day at the aforementioned time. During the aforementioned time, the TTA advance index operates the hour servo system to move the hour sound head to the three AM or two AM track as required by the position of the daylight switch. A 5-bit memory latch is operated in the hour monitor circuit 69 and it will hold its previous indication until 02:00:00. The daylight flip-flop adds a binary 1 to the 24 hour local clock's hour output to provide daylight savings time to the TTA apparatus. Hour advance index logic circuit 70 provides the output signal through code holding latch 42 to advance the hour sound head to the required track via step motor 110.

The 24 hour time is applied to 24-hour-to-12-hour clock 68 via daylight savings time preset circuit 66. Hour advance index logic circuit 70 generates a control signal via hour motor servo amplifier 72 through code holding latch 74 which is actuated by hour servo enable signals, the generation of which will be described supra. Minute advance index logic circuit 76 receives the output from binary minute clock 52 to generate control signals for minute motor servo amplifier 78. The control signals for seconds motor servo amplifer 80 is generated by circuitry to be described supra. The control signals for minute motor servo amplifier 78 and seconds motor servo amplifier 80 are controlled by code holding latches 82, 84, respectively. Code holding latches 82, 84 receive respective signals for releasing the control signals to the motor servo amplifiers by circuitry which will be described hereinafter.

The monitor switch 86 enables either GMT, the local 24-hour or the local 12-hour clock signals from daylight savings time preset circuit 66, 24-hour-to-12-hour clock converter 68, or hour advance index logic circuit 70, to be monitored by hour monitor 69. The outputs from binary minute clock 52 and binary second clock 54 are respectively monitored by minute monitor 90 and seconds monitor 92. The hour monitor 69, minute monitor 90 and seconds monitor 92 may preferably comprise Nixie readout circuitry which is well known to those skilled in the art.

The conversion of actual GMT to local hour time is accomplished by adding the 24 hour complement number representing the GMT latitude time zone offset for the local time to the GMT hour. The GMT minutes are unchanged. For example, EST for the winter months is 5 hours behind the GMT. The 24 hour complementary number is therefore 19. The logic circuits within the GMT-to-local 24 hour time circuit 64 add the 5-bit code representing the GMT to the 5-bit complementary zone offset number as long as the GMT hour is less than 24. When the sum of the 5-bit code representing the GMT hour and 5-bit complementary zone offset code exceeds 23, which is detected when the binary code's two most significant digits are one, an additional binary 8 is added to the total. This number is entered in the 6th and nonexistent bit. The remaining 5-bit code represents the 24-hour local time period. 24-hour-to-12-hour clock 68 has a switched output enabling either 24-hour or 12-hour clock signals to be generated therefrom, and the output of clock 68 is fed to hour remote equipment shift register 94. The outputs from binary minute clock 52 and binary seconds clock 54 are also respectively fed to minute remote equipment shift register 96 and seconds remote equipment shift register 98. Shift registers 94, 96, and 98 are controlled by clock pulses from clock line 100 with which clock pulses are generated by remote equipment logic clock 102. The shift register data entry is parallel and comprises a 5-bit signal from 24-hour-to-12-hour clock 68 and 6-bit signals into each of minute remote equipment shift register 96 and seconds remote equipment shift register 98. The output of seconds remote equipment shift register 98 to seconds motor servo amplifier 80 is additionally controlled through code holding latch 84 by seconds count signal 102 which is generated by equipment to be described supra.

24-hour-clock-to-12 hour clock 68 operates in the following manner to accomplish the 24-to-12 hour local time conversion. The hour "00" is detected and a binary "12" is added to the 5-bit hour code. (The hour "00" represents 12 midnight.) The hours "01" to "12" remain unchanged (this represents 12 noon). The hours "13" to "23" are detected and a binary "20" is added to the 5-bit hour code that enters the sixth and non-existent bit. The remaining 5-bits represents the afternoon and evening hours "1" to "11". The output of clock 68 may be changed to either 12 or 24 hour format by simply inhibiting the logic code detectors during the 24 hours operation. Inasmuch as the TTA system of this invention has both 12 and 24 hour recordings on the recording tracks, the format may be instantly changed. The format switch in the clock circuit also corrects the hour advance index logic circuit 70 to cause it to operate properly.

Remote equipment shift registers 94, 96, 98 are parallelly set by the respective local hour, minute and seconds time as well as official temperature applied to the circuitry to be described supra. Remote equipment, logic clock 102 transmits a signal 4 times per second on clock line 100 to control the shift registers. The output of hour remote equipment shift register 94 is fed to telephone central office dial tone generator 104 and telephone digital line driver 106 for transmission of information to a sponsor's remote location. Inasmuch as audio information is also transmitted over the same pair of telephone wires on a time-sharing basis, the output from telephone digital line driver 106 is gated through the aduio/digital time/temperature phone line via audio/digital gate relay 108 which receives a synthesized audio input control signal 109 from circuitry to be described supra. The output from audio/digital gate relay 108 may be used at the sponsor's premises for correct time and official temperature displays as well as to control electrical outdoor advertising signs. The output from telephone central office dial tone generator 104 enables all subscribers within the telephone company's operating area to automatically set digital clocks, or other digitally operated equipment, on their premises by lifting the phone off the hook or dialing the telephone central office to receive the dial tone generator information.

Each of the motor servo amplifiers 72, 78 and 80 comprise digital logic compare circuitry (to be described more fully hereinafter) for comparing the incoming binary code with an 8-bit binary code derived from the 8-bit modified Gray code converter. The outputs of motor servo amplifier 72, 78 and 80, respectively drive hour step motor 110, minute step motor 112 and seconds step motor 114 and respectively receive an input from encoders 116, 118 and 120. Encoders 116, 118 and 120 generate feedback information through an electromechanical feedback network from each of the respective step motors.

The temperature data for the TTA system is received from a remote location such as a weather bureau which is often located at an airport and is generated by the circuitry illustrated in FIG. 2. The temperature sensor is a nickel-resistance thermometer, type 1-A manufactured by Minneapolis Honeywell Company and is mounted for example in a wood-louvered enclosure 140. The output of thermometer 140 is fed to resistance reference measuring bridge circuit 142 via a cable which may be as much as 1000 ft. in length. The range of temperature measurement is from minus 40.degree. to plus 120.degree. F. and is provided to thermometer servo amplifier 144, the output of which drives servo motor 146 which in turn controls the rotation of modified Gray code encoder wheel 150 which is mounted between light emitting diodes 152 and phototransistors 154. Servo feedback precision potentiometer 156 is driven by servo motor 146 to provide a feedback signal to servo amplifier 144.

The temperature sensing circuitry just described is a proven reliable system in which 20 year calibration stabilities of plus or minus 1/2.degree. F. can be expected over the entire 161.degree. temperature range. The non-linearity of the 60 Hz bridge circuit and the resistance thermometer is compensated by the uneven spacing of the combinations on encoder wheel 150 which will be more fully described hereinafter. For example, minus 40.degree. to a minus 39.degree. F. represents less than 1.degree. of rotation whereas plus 119.degree. to plus 120.degree. F. is more than 1.degree. of rotation.

A Gray code is a minimum change code which means that the output changes only one bit at a time. The two most significant bits on encoder wheel 150 are inverted so that the metal wheel will be mechanically strong. Additionally, the inversion of the two most significant bits that are converted from Gray code to binary code is accomplished by special logic circuitry to be described supra. The output of phototransistors 154 is fed to modified Gray code-to-binary code converter 158 and the output of converter 158 is displayed by temperature monitor 160. The binary number 100 assigned to 0.degree. F. which allows both positive and negative values of temperature to be indicated and which corresponds exactly with the temperature recordings recorded on the TTA record mechanism. The 8-bit parallel binary output from converter 158 is fed to shift register 160 which converts the binary code from parallel to serial format. The serial code is fed to telephone line driver 162 for transmission over a pair of telephone wires 163 to the telephone control office at which the TTA system is rotated. Shift register converter 160 is controlled by the output clock pulses from logic clock generator 164 which output comprises a 10 pulse per second burst every minute.

The thermometer and A/D converter circuitry as well as the necessary logic circuitry are powered from battery 166. Automatic battery charger 168 is provided to obtain continuous service of the equipment. The necessary voltages to operate the thermometer circuitry are provided from power supply 169 which is energized from battery 166.

The serially coded temperature data transmitted over the telephone lines 163 is received at the central office and fed to telephone digital line decoder 170 as illustrated in FIG. 3. Telephone digital line decoder 170 generates a start signal for temperature logic clock generator 172 and also a control signal for temperature shift register 174 which receives the output of logic clock generator 172. The clock output comprises 10 pulses per second on command from the telephone digital line decoder 170. The output of temperature power shift register 174 is temporarily stored in temperature step motor servo amplifier 176 via temperature code holding latch 178 which is actuated by temperature servo enable signals 180, the generation of which will be described more fully hereinafter. The output of temperature parallel shift register 174 is monitored by temperature monitor 182 and also fed to temperature remote equipment shift register 184 where it is temporarily stored until provided to the chain of remote equipment shift registers 94, 96, 98 under control of clock pulses from remote equipment logic clock 102. Temperature step motor servo amplifier 176 is similar to motor servo amplifiers 72, 78 and 80 and drives temperature step motor 186 by comparison of the input temperature code with the output of 8-bit encoder 188 which represents a feedback from temperature step motor 186.

The following is a description of the quartz oscillator and record position synchronization system illustrated in FIG. 4. 3,932,160 Hz free-wheeling crystal oscillator 190 has a stability of 5 parts in 10.sup.-.sup.8 per day. The frequency of oscillator 190 is selected so that its fundamental or harmonics do not interfere with the WWV signal, and that frequency is also a suitable binary multiple of 60 Hz. The output of oscillator 190 is divided by 16 to a frequency of 245,760 Hz by means of divider 192. The output of divider 192 is divided by 64 to a frequency of 3,840 Hz by divider 194. The output of divider 194 is also divided by 2 to 1920 Hz by divider 196. Output 199 provides the master clock with a continuous counting frequency and also supplies the clock drive for the radio IRIG decoder output. The output of divider 196 is divided by 2 by divider 198 and the output 200 thereof is used to provide the 960 Hz audio marker tone in the message announcement.

One shot multivibrator 202 is driven by input 204 to provide a 20 microsecond output reset pulse to dividers 206 and 208 and terminal 210 for use in the audio synthesizer. One pulse/minute input 204 is present each time when the master clock is exactly at zero seconds. The 3840 Hz output from divider 194 also drives divider 206, that divides by 300 to 12.8 Hz. The output of divider 206 drives divider 208 that divides to provide outputs of 6.4 Hz, 3.2 Hz, 1.6 Hz, 0.8 Hz, 0.4 Hz, and 0.2 Hz. These outputs are connected to the input of 8-bit digital comparator 212.

Flip-flop 214 is driven by the 0.2 Hz output of divider 208 and generates a special bit for the purpose of determining the shortest correction time (and thus the direction of correction) for synchronizing the audio recordings with the actual time announced.

The output of divider 192 is also applied to the input of programmable divider 216 which operates so that the number of divisions maay be altered to any one of three conditions. When output 218, A > B, of 8-bit digital comparator 212 is generated, divider 216 divides by 63 to provide an output frequency of 3,900.95 Hz. When A < B appears at output 220, divider 216 divides by 65 to provide an output frequency of 3,780.92 Hz. When no output occurs from 8-bit digital comparator 212, or A = B appears at output 222, divider 216 is then programmed by program control 217 to divide by 64 to generate an output of 3,840 Hz. The purpose of programmable divider 216 is to provide a means of adjusting automatically the frequency that controls the speed of the record drum so that its prerecorded time announcements may be positioned to provide composite voice announcements that are synchronized precisely with the National Bureau of Standards Time Code.

Divider 224 divides the output of divider 216 by 64 to generate main drive motor frequencies of 60.95 Hz, 60.0 Hz, or 59.08 Hz depending on the outputs 218, 220 and 222 and the programming of divider 216. Power amplifier 226 amplifies the output of divider 224 to drive synchronous 1,800 RPM main drive motor 228.

The output of divider 216 is also applied to divider 230 that divides by 30 to an output frequency of approximately 128 Hz which is applied to divider 232 to provide an output 234 of approximately 32 Hz that operates the voice message synthesizer. The output of divider 220 also drives divider 236 that divides by 10 to an output frequency of approximately 12.8 Hz which is applied to divider 238. The outputs of approximately 6.4 Hz, approximately 8.2 Hz, approximately 1.6 Hz, approximately 0.8 Hz, approximately 0.4 Hz, and approximately 0.2 Hz are connected to 8-bit digital comparator 212. The 0.2 Hz output drives special flip-flop 240 which divides by 2 and the output thereof is applied to comparator 212. Flip-flop 240 is reset by the 0.2 Hz output of divider 208. Schmitt Trigger 242 is driven by a signal from the optical interrupter switch 244 on the second drum. The record drum is driven by hysteresis synchronous motor 228 from the 60 Hz supply that causes it to operate at 1,800 RPM. This speed is reduced by a gear ratio of 150:1. The rotational speed of the record is 12 RPM. This provides a position output of optical switch 244 at the rate of once each five seconds. The output of Schmitt trigger 242 is applied to one shot multivibrator 246 to provide a 20 microsecond reset pulse output for dividers 224, 226, 232, 236, 238 and 240 and an output 248 for use in the audio synthesizer.

The program for programmable divider 216 is changed under the control of the digital comparator outputs 218, 220 and 222. A > B when the record position determined by the optical switch 244 is slow in relation to the actual time. With respect to FIG. 5, the A > B output 218 is applied to NAND gate 250. When binary dividers 252, 254 have reached a binary code of 0111111 or 63, the two NAND gates 256, 258 produce low outputs that are applied to NOR gate 260. The "2" output of divider 254 is also applied to NOR gate 260. A high output from NOR gate 260 is applied to NAND gate 250 which produces a low output that is applied to NAND gate 262 which provides a high output when a low input is applied to either input terminal. The high output of NAND gate 262 is applied to the B input of one shot multivibrator 264 which resets dividers 252, 254 with a 35 NS pulse at a rate of 3,900.95 Hz. The 60 NS pulse output 266 from NAND gate 262 is used also to drive the main drive motor divider chain and the 32 Hz output for the voice synthesizer input. This is the "speed up" operation of the system and represents division by 63.

A = B when optical switch 244 is exactly in the "on time" position. Comparator output 220 is now low at both the inputs 5 to binary divider 252. NOR gate 268 now has a high output when binary code 1000000 is reached which represents division by 64, and that output is applied to NOR gate 270 that is arranged so that a high input on either input terminal will result in a low output. The output of NOR gate 270 is applied to NOR gate 272 along with the B and C low outputs of divider 252. The three inputs to NOR gate 274 are connected to the low output D of divider 252 and the E and F low outputs of divider 254. The high outputs of NOR gates 272, 274, and the G output of divider 254 are connected to NAND gate 276, the low output of which is connected to the input of NAND gate 262 that provides a high output from either low input. The output of NAND gate 262 is applied to the B input of oneshot multivibrator 264 that reliably resets dividers 252, 254 at a rate of exactly 3840 Hz. The output of NAND gate 262 is also applied to terminal 266 for the main drive motor divider chain and the voice synthesizer divider chain. This is the normal operating condition for this system with an even division of 64.

A < B when the optical switch interrupter 244 mounted to the record drum is "fast" in relation to the actual time. Output 222 is high and input 218 is low. Output 222 is applied to NAND gate 276 and when the binary code reaches 1000001 or 65 a high is applied to the other input of gate 276. A low output from gate 276 is applied to the input of inverter 278. The high output of inverter 278 is applied to the input of NOR gate 270 so that either high input will provide a low output. The low output of gate 270 along with outputs B and C of binary divider 252 is applied to the three inputs of NOR gate 272. Low outputs D of divider 252, outputs E and F of divider 254 are applied to NOR gate 274. The high outputs of gates 272, 274 and output G of divider 254 are applied to the three inputs of NAND gate 280. The low output of gate 280 is applied to NAND gate 262 which provides a high output with either input low. The high output of gate 262 is applied to oneshot pulse circuit 264. This reliably resets dividers 252, 254 at a rate of 3780.92 Hz. The output of gate 262 is also applied to terminal 266. This is the slow operating condition for this system with a division of 65.

The correct relation between the composite voice announcement and the master clock that is set by the National Bureau of Standards Time Code, is necessary for precision time announcements. The voice announcements are recorded on the magnetic record drum so that the composite announcement will end just prior to the 960 Hz marker tone that originates in the logic circuits to define the exact time. An interrupter, attached to the record drum that operates optical switch 244 is used to locate position of the announcement bits during the original recording. When played back, the end of all of the composite announcements will occur just prior to the switch operation. The system requires synchronization of this switch with the actual even 5-second intervals of the composite announcements.

This is accomplished by comparing the outputs A, B, C, D, E, F and G of dividers 206, 208 (FIG. 4) with the outputs A', B', C', D', E', F' and G' of dividers 236, 238 by a 7-bit digital comparator 212. Dividers 206, 208 are reset once per minute by the master clock at exactly the beginning of each minute. As long as the quartz oscillator is exactly on its designed frequency and its divider chain is not disturbed after the initial set, the reset pulse will be synchronous with dividers 206, 208 and make no correction unless the master clock is in error and a WWV update resets it. Outputs A, B, C, D, E, F and G form a 7-bit binary code.

Dividers 224, 230, 232, 236 and 238 are reset by the optical record drum switch 244 every five seconds. Upon start-up, after the initial reset of these dividers, outputs A', B', C', D', E', F' and G' form a 7-bit binary code. This code represents one of the 128 digital positions that the record drum may be in as related to the position code synchronized and defined by the master clock. These positions represent 39 millisecond increments.

Digital comparator 212 will define A > B, A = B, or A < B. The 8th and the most significant bit is used as a special bit to define the direction that will provide the quickest correction that should be made when A is not equal to B. This is accomplished by cross coupling the output of divider 208 with the reset of divider 240 and the output of divider 238 with the reset of divider 214. Furthermore this arrangement causes the selected direction to be continuous until A = B. This servo control is accomplished by changing the programmable divider 216. This causes the record drum to speed up to 12.19 RPM or 4.92 second per rotation when A > B, or slow down to 11.82 RPM or 5.08 seconds per rotation when A < B. The normal record drum speed is 12 RPM or 5 seconds per rotation when A = B.

As the servo correction approaches the A = B condition, an unexpected result occurs. It would appear that the A = B condition would be 1/128th of the record rotation when the least significant bits were equal, limiting the resolving ability of the system to 39 milliseconds. Actually, when the least significant bits are equal, any phase difference between the divider chains appears on the A > B or A < B outputs 218, 222 as a 12.8 Hz pulse with a variable width depending on the magnitude of the phase difference. As the pulse width narrows, the number of fast or slow corrections decreases providing a very smooth phase sensitive proportional control of the final record position. This provides a measured 2 millisecond position accuracy of the system.

The voice message synthesizer illustrated in FIG. 6 switches and synchronizes the magnetic head outputs to assemble the three composite message announcements that are provided to the calling telephone subscribers. Voice synthesizer reset output 210 (FIG. 4) is a 32 Hz signal synchronized each five seconds with the record switch. The 1800 RPM main drive motor and its 150 to 1 gearing turns the record drum one revolution each five seconds to provide a reset switch operation each 160 cycles of the motor driving power, normally making no correction. When programmable divider 216 is either fast or slow, there is normally no correction due to switch operation because the system's related parts are all synchronous even when the output frequency of programmable divider 216 changes. Only at start-up, or due to an abnormal disturbance, is the relationship between record drum switch 244 and 32 Hz divider 232 corrected.

With respect to FIG. 6 the 32 Hz at input 204 is divided by 16 by divider 292 to 2 Hz. The 2 Hz signal is divided by thirty and counted by dividers 294, 296. NAND gate 298 detects binary number 11110 or (30) and its low output is applied to oneshot multivibrator 200 that produces a 1 microsecond pulse on terminals 1 and 6 thereof to reliably reset dividers 292, 294 and 296. This provides a continuous binary count of 0 to 29, changing each one-half second and recycling four times per minute.

NAND gate 302 produces a low output when the digital comparator 212 output 220 (FIG. 4) at one input terminal is high indicating A = B and the one pulse per minute input is high at the other input terminal that is supplied from the radio set master clock exactly at the beginning of each minute. The low output of NAND gate 302 is applied to input 4 of oneshot multivibrator 300, thereby initiating the reset of dividers 292, 294 and 296 once each minute. In the event that the record position switch is not in the zero degree position with respect to the binary input code, defined by A > B or A < B, this circuit will not correct the voice message synthesizer until A = B. Once synchronized with the WWV radio set master clock and the quartz oscillator is exactly on its design frequency of 3932160 Hz no further corrections will occur as the system is synchronized with the actual time within a few milliseconds. The cycle will repeat automatically if the system is disturbed or set "off time". Number decoders 304 and 306 are arranged to decode the outputs of counters 294, 296 into 30 1/2 second output pulses every 15 seconds. Decoder 304 is activated by the low output of counter 296. When the count beginning at zero has reached 15, counter 296 switches off decoder 304 and switches on decoder 306 for counts 16 to 29. Counter 296 switches on decoder 304 again at the count of zero. This provides 30, one-half second serial low output pulses on the 30 output leads of decoders 304 and 306 every 15 seconds. The zero count starts exactly at the zero second, 15th second, 30th second, and the 45th second, or 4 times per minute.

Oneshot circuit 308 is used to reset dividers 310 and 312 once each minute when A = B. These dividers are also synchronous, and after their initial set continue to operate without further correction. Divider 310 divides the 2 Hz signal to 0.2 Hz. Divider/counter 312 advances one count each 5 seconds from 0 to 11, and resets in 10 microseconds on the count of 12. Outputs 313, 314, 315 and 316 provide for the advance of the message/seconds servo, once each 5 seconds.

The outputs of decoders 304 and 306 are applied to a series of NAND gates 318-346 (FIG. 7) arranged to provide the various combinations of counter pulses to produce the synchronized high outputs for the control of switching the five magnetic head preamplifier outputs. This provides a three channel voice message synthesized output each beginning at intervals of five seconds and providing a complete composite announcement including a control pulse.

EXAMPLE 1.

0.4 sec. channel No. 1 trunk CT pulse.

(Good morning) (This is another service of the First National Bank) (The present official temperature is 70 degrees) (Daylight time is) (9 hours) (45 minutes) (exactly) (0.1 sec. 960 Hz tone). The first cycle of the 960 Hz tone is exactly on time.

EXAMPLE 2.

(0.4 sec. channel No. 2 trunk CT pulse).

(Good morning) (The First National Bank pays 4 percent interest on passbook savings accounts) (The present official temperature is 70 degrees) (Daylight time is) (9 hours) (45 minutes) (and 5 seconds) (0.1 sec. 960 Hz tone).

EXAMPLE 3.

(0.4 sec. channel No. 3 trunk CT pulse).

(Good morning) (Start your business with the use of a First National Bank Loan) (The present official temperature is 70 degrees) (Daylight time is) (9 hours) (45 minutes) (and 10 seconds). (0.1 sec. 960 Hz tone).

TABLE 1 __________________________________________________________________________ Time in Voice synthesizer Total of 341 recording bits on record. seconds 1/2 sec. clock count Three channels of composite __________________________________________________________________________ announcements. 30 Sec. 0 Switch operates Ch. No. 1 Ch. No. 2 Ch. No. __________________________________________________________________________ 3 960Hz tone (Msg. 9) 1 Trunk C.T. Daylight Way to 31 Sec. 2 Good time is security Msg./Sec./Temp. -- -- 3 index evening 32 Sec. 4 This (msg. Eleven The 10) 5 is Hours present 33 Sec. 6 another Fifty official nine 7 service minutes temperature and 34 Sec. 8 of The thirty is five 9 First seconds seventy-one 35 Sec. 10 National degrees 960Hz-tone 11 Bank Trunk C.T. Daylight 36 Sec. 12 Good Time is Msg./Sec./Temp. index -- -- 13 Evening 37 Sec. 14 The The (msg. 11) Eleven 15 Present First Hours 38 Sec. 16 Official National Fifty Bank Nine 17 Temperature Pays Minutes 39 Sec. 18 is four and forty 19 seventy percent seconds 40 Sec. 20 degrees on 960Hz tone 21 Daylight savings trunk C.T. pulse 41 Sec. 22 Time is accounts Good Msg./Sec./Temp. -- -- 23 index Evening 42 Sec. 24 Eleven The Start (mgs. 12) 25 Hours present your 43 Sec. 26 fifty-nine 27 minutes official business 44 Sec. 28 and temperature by the is 29 forty-five seventy use of 45 Sec. 0 seconds degrees a First 960Hz tone 1 trunk C.T. Daylight National 46 Sec. 2 Good Time is savings account Msg./Sec./Temp. -- -- 3 index Evening 47 Sec. 4 Personal eleven The (msg. No. 1) 5 loans hours present fifty- 48 Sec. 6 are nine official 7 your minutes temperature 49 Sec. 8 best and is 9 bet fifty seventy The 50 Sec. 10 First seconds degrees 960Hz tone 11 National trunk C.T. Daylight 51 Sec. 12 Bank Good Time is Msg./Sec./Temp. -- -- 13 *Daylight index evening 52 Sec. 14 The Auto (msg. eleven No. 2) 15 present loans hours GM and Hr. 53 Sec. 16 Adv. index official are fifty 17 temperature available nine minutes Minute 54 Sec. 18 Adv. index is at low and 19 seventy one interest fifty five 55 Sec. 20 degrees rates at seconds 960 Hz tone 21 Standard First trunk C.T. pulse 56 Sec. 22 Time is National Radio set of Good master clock, msg. -- -- morning sec. 23 Temp. index 57 24 twelve The 25 hours present Safety (msg. No. 3) 58 26 zero official deposit 27 minutes temperature boxes 59 28 is secure 29 exactly seventy one valuables 0 0 degrees The First Master clock 960Hz tone 1 resets voice prog. trunk C.T. pulse Standard National 1 2 Good Time is Bank Msg./Sec./Temp. -- -- 3 index morning 2 4 The (msg. twelve The No. 4) 5 First hours present 3 6 National zero official 7 Bank's minutes temperature 4 8 Trust and is 9 department five seventy 5 10 serves seconds degrees 960Hz tone 11 your trunk C.T. Standard 6 12 needs Good Time is Msg./Sec./Temp. -- -- 13 index morning 7 14 The The (msg. twelve No. 5) 15 present First hours 8 16 official National zero 17 temperature Bank minutes 9 18 is makes and 19 seventy ten 10 20 degrees second seconds 960Hz tone 21 Standard mortgage trunk C.T. pulse 11 22 Time is loans Good Msg./Sec./Temp. -- -- 23 index morning 12 24 twelve The Auto (msg. No. 6) 25 hours present repairs 13 26 zero official can 27 minutes temperature be 14 28 and is expensive 29 fifteen seventy see 15 0 seconds degrees The First 960Hz tone 1 trunk C.T. pulse Standard National 16 2 Good Time is Bank Msg./Sec./Temp. -- -- 3 index morning 17 4 Title twelve The (msg. No. 7) 5 searches hours present 18 6 and zero official 7 warranties minutes temperature 19 8 are and is 9 services twenty seventy 20 10 of The seconds degrees 960Hz tone pulse 11 First Nat- trunk C.T. Standard ional Good 21 12 Bank Time is Msg./Sec./Temp. -- -- 13 index morning (msg. No. 8) 22 14 The twelve 15 present Save hours 23 16 official a lot zero 17 temperature or save minutes 24 18 is a little and 19 seventy at The twenty-five 25 20 degrees First seconds 960Hz tone 21 Standard National trunk CT pulse 26 22 Time is Bank Good Msg./Sec./Temp. -- -- 23 index morning 27 24 twelve The A (msg. 9) 25 hours present First 28 26 zero official National 27 minutes temperat- Bank ure 29 28 and is savings 29 thirty seventy account 30 0 seconds degrees is a __________________________________________________________________________ *The Daylight/Standard Time index occurs at 01:59:51 on the last Sunday morning of October and the last Sunday morning of May. The change from Daylight to Standard time is shown on the sample program at 11:59:51 for demonstration only.

Examination of the program layout shown in Table 1 shows exactly how the various voice segments are compiled into the three composite announcement output. With the change of time and temperature the binary code to the servo amplifiers is changed accordingly at the allowable points in the cycles of the three composite announcements. The index (or servo latch) is updated so that the new codes will cause the proper servo systems to position the magnetic heads so that no announcement is disturbed during the change.

The arrangement of the various gates required to compile composite announcements is illustrated in FIG. 7. The circuits are self-explanatory and their outputs are identified. The output marked 416 "GE Start" is used to start the cued up tape recorder one-half second before the beginning of the message segment to be recorded. The tape recorder has the original voice master recording for a specific bit that the announcer made for that location on the record drum. This facilitates the pre-recording of the record drum with precise location of the bits and with the savings of many hours during the recording of the 341 bit segments. After the drum is recorded, the tape machine is disconnected and these outputs serve no further function. The 960 Hz marker tone 200 is derived from divider 198 of FIG. 4. An active filter may be used to change the 960 Hz square wave divider output to a 960 Hz sine wave. The function of the 960 Hz sine wave will be described more fully hereinafter. However, the 960 Hz sine wave is gated by an analog switch associated with the power amplifier of each channel under the control of outputs 463, 424 and 425 (FIG. 7). The length of the pulse may be controlled by a suitable time constant circuit in the active filter and is adjusted to approximately 100 milliseconds. The remainder of the one-half second pulse from the decoder (FIG. 7) is used for the trunk cut through (CT) pulse for the same channel. This pulse also serves as the trunk cut-off (CO) pulse at the end of the announcement cycle for that channel.

As can be seen from the logic diagram in FIG. 7 the 30, one-half second output pulses from FIG. 6 are added together to form the desired combination of bits for the necessary segments. To save logic hardware, various short segments are added together to provide the longer segments where they are needed in the announcement program.

Example: Beginning at the time of 31.5 seconds, one-half second serial clock counts 3 and 4 are added together to provide the 1 second gate operation for channel 2 (11 hours). Counts 5 and 6 are added together to provide the 1 second gate operation for channel 2 (59 minutes). Counts 7, 8 and 9 are added together for the 1 1/2 second gate operation for channel 2 (and 35 seconds). The counts for the channel 2 hours, minutes and seconds are added together to provide the gate control operation for channel 3 (the present temperature is 71.degree.). Counts 10 and 11 are added together to provide the (Daylight Time is) for channel 3. The counts for channel 3 (Temperature) are added to the counts for channel 3 (Daylight Time is) segment. This combination provides the 4.5 second gate operation for the message announcement on channel 1 (counts 3, 4, 5, 6, 7, 8, 9, 10 and 11). The message segments are generated in this manner for the entire three channel program as defined by FIG. 7. By changing the arrangement of the record drum recordings and the logic of FIG. 7. an entirely new program may be composed.

The detail circuitry comprising the step motor digital servo amplifier is illustrated in FIG. 8. Plus five volts DC is applied to servo amplifier connector 450 at terminal number 10 and is also applied to the collectors of the eight phototransistors located in the optical encoder. Plus 24 volts DC is applied to the common lead of the four step motor coils and to the eight series-connected infrared light emitting diodes located on the opposite side of the optical encoder. An eight-bit 256 linear encoder plate 848 (FIG. 14) is mounted to the carriage assembly and has the magnetic head also mounted on it. The carriage may be mechanically positioned to any one of the 256 tracks on the magnetic record by the "ball screw and nut" assembly that is connected to the servo step motor. When the motor rotates 90.degree., the carriage and the encoder plate move exactly one 8-bit code number, and the sound head moves exactly one record track. The number is defined as a modified 8-bit Gray code by a series of holes and spaces matching the code format. The encoder plate is mounted between the eight LED's and the eight phototransistors to provide an 8-bit output that is connected to servo amplifier input terminals 11 to 18 on connector 450. Terminals 11-14 are connected to Schmitt trigger circuit 452 and terminals 15-18 are connected to Schmitt trigger circuit 454. A 220 K resistor (not shown) is connected between each input terminal 11 to 18 and ground to stabilize the lower trigger point of the respective Schmitt triggers within Schmitt trigger circuits 452 and 454. The presence of a hole on the encoder plate between the LED's and the phototransistors, causes a high level logic signal to be generated at the output of Schmitt trigger 452 or 454. The absence of a hole provides a low level logic output. The two most significant bits of the Gray code on the encoder plate are mechanically inverted so that encoder plate 848, after chemical milling, will be mechanically strong. A correcting logic inversion is made by exclusive OR gate 456 and NAND gate 458 from the indicated output of Schmitt trigger 454.

An 8-bit Gray code is preferred because it enables the mechanical tolerance of the optical encoder element to be greater than the tolerance of a corresponding 8-bit natural binary code. As explained previously, the Gray code changes only one bit at a time for each of the 256 binary numbers, whereas the natural binary code changes all 8 bits at once to any given number change, making an exact mechanical alignment extremely difficult. Therefore, logic circuitry is necessary for changing the Gray code to a natural binary code. This logic circuitry is formed by exclusive OR gates 460, 462, 464, 466, 468, 470, 472 which respectively receive one of the seven outputs from Schmitt trigger circuits 452 and 454. The outputs of exclusive OR gates 460-472, along with the output of exclusive OR gate 456 are applied as "B" inputs to 4-bit digital comparators 474, 476.

The 8-bit natural binary code connected to input terminals 2 to 9 of connector 450 of the servo amplifier circuitry originates in external logic circuitry described elsewhere and the number represented by the binary code input represents one of the desired 256 track positions for the location of the magnetic sound head. That eight-bit natural binary code is applied to the "A" inputs of the two 4-bit digital comparators 474 and 476.

Digital comparators 474, 476 have three output terminals 478, 480 and 482 for respectively providing signals indicating A > B, A equal to B, and A < B. The 478 output drives the servo motor in an up direction, the 480 output holds the servo motor in a given position, and the 482 output drives the servo motor in a downward direction. NAND gates 484, 486, 488 determine the direction of operation of up/down counters 490, 492 from the signals on terminals 478, 480 and 482. When the input logic number is greater than the number of the encoder position, that is A > B, output 478 of digital comparator 476 is high and outputs 480, 482 are low. The output 480 is applied to NAND gate 488 and causes its output to go high and initiates operation of clock 494 which generates a 1 millisecond high output pulse every 8 milliseconds to advance counters 490, 492 in the UP direction. The direction of operation of counters 490, 492 in this instance is determined by the output from NAND gate 484. The eight position counters 490, 492 are thereby advanced in the UP direction with the aid of the logic outputs from NAND gates 496, 498 and 500. Binary coded decimal-to-decimal decoder 502 decodes the eight position output of up/down counter 492 into digital numbers from zero to seven. The output of decoder 502 is encoded into the logic pattern that causes the step motor to step eight steps per revolution and is accomplished by step detent logic AND gate 504, 506, 508, 510, 512 and 514. The output of gates 504-514 drives power transistors 514, 518, 520 and 522, the outputs of which appear at terminals 19-22 of connector 450 for drivng the step motors. The output stepping logic is: AB = 1, B= 2, BC = 3, C = 4, CD = 5, D = 6, DA = 7, A = 0. Counters 490, 492 are counting in the UP direction and continue to do so until the output of comparators 474, 476 indicate that A = B. The clock drive circuitry will stop the step motor in one of four positions, namely AB = 1, BC = 3, CD = 5, or A = 7. A high output at terminal 524 of up/down counter 490 causes decoder 502 to indicate an additional output in the event A = B before the step motor has reached one of the detent holding positions. This is determined by NAND gate 484. The reason for the eight steps per revolution of the step motor instead of four steps per revolution, is due to the step motor rotor inertia in the high speed stepping rates. There is much less over-run with 45.degree. steps than with 90.degree. steps for any given stepping rate; and therefore the eight steps per revolution is preferred.

When the output of comparator 476 indicates that A < B the count down logic is exactly opposite of the previous description and NAND gates 484, 486 and 488 control up/down counters 490, 492 to count in a down direction. Thereby, the step motor is driven in the reverse direction until the output of comparator 476 indicates that A = B.

The eight-bit parallel binary code represented by the shift register 160 in FIG. 2 appears at terminals 2-9 of connector 530 in FIG. 9, which represents the circuitry comprising temperature monitor 159 (FIG. 2). The eight-bit binary number input is converted into a binary coded decimal code by binary-to-binary coded decimal encoders 532, 534 and 536, the outputs of which are connected to binary coded decimal decoder drivers 538, 540 by AND gates 542, 544, 546, 548, 550, 552, 554 and 556; as well as OR gates 558, 560, 562, 564, 566, 568, 570 and 572; adder 574; and NAND gate 576. The Nixie readout indicator tubes 588, 590 are connected to the binary coded decimal decoder driver outputs as indicated in FIG. 9. Nixie readout indicator tubes 588, 590 will indicate temperture from minus 99.degree. to plus 155.degree. F. when a mode control input at terminal 10 of connector 530 is low.

As has been explained previously, zero temperture is assigned the binary number 100. The binary coded decimal output from binary-to-binary coded decimal encoders 532, 534, 536 are now applied to binary coded decimal complement converter 592 and the binary coded 9's complement converter 594 when there is a negative value of temperature. The output of complement converter 592 is connected to number decoder 538 through AND gates 542, 544 and 546. The outputs of binary coded decimal complement 9's converter 594 is applied to ADDER 574 so that when the least significant digit is zero, a binary one is added. The output of adder 574 is fed to binary coded decimal number decoder 540 through NAND gate 596. The output of decoder 540 is connected to Nixie tube indicator 590. For positive values of temperatures, OR gates 558, 560, 562 by-pass complement converters 592, 594 out of the circuit.

When the mode control input at terminal 10 of connector 530 is high, Nixie readcout tubes 598, 600 will indicate numbers 0 to 255 (representing the full 8-bit binary number input). The necessary logic for driving Nixie indicator tubes 598, 600 comprises NOR gates 602, 604 and 606; AND gates 608, 610, 612 and 614; NOR gates 616, 618, 620 and 622; as well as driver transistors 624, 626, 628, 630 and 632.

The TTA system's master clock is set by radio signals from WWV and operates exactly "on time". For the correct voice announcement, the machine must advance the hour and minute one announcement prior to the actual time change. The circuitry for accomplishing this is the hour advance index logic circuit 70 and the minute advance index logic circuit 76 illustrated in FIG. 3 and illustrated in more detail in FIG. 10. The clock hours, clock minutes and clock seconds respectively from 24 hour clock 68, set minute clock 52, and set seconds clock 54 (FIG. 3) are provided as inputs to logic circuit 650, which comprises an assemblage of NAND, NOR, and AND inverter circuitry for generating the necessary control signals to operate the hour and minute advance index logic circuitry. Logic circuit 650 provides the following output control signals: Add 8 hours, add 20 hours, add 1 hour, add 4 minutes, and add 1 minute. As described previously, the advancement of the hour and minute by one announcement cycle prior to the actual time change is accomplished by detecting the hour 12:59:52 and adding a binary 21 to the 5-bit hour binary number. The necessary addition is accomplished by adder circuits 652, 654 and 656. The hour servo amplifier's input code now appears as 1 o'clock and the servo system changes the hour sound head's track position to 1:00 o'clock and the hour enable pulse occurs 5 1/2seconds before the actual time of 1 o'clock. The "1" hour is announced in advance of the 960 Hz tone that begins precisely at the start of hour "1". All other hours have a binary 1 added during the 5 1/2 second period.

The logic for the 24 hour clock detects the hour 23:59:52 and adds a binary 9 to the 5-bit binary hour code. The hour's servo amplifier's input code thereby appears as "0" hours and the servo system changes the hour sound head's track position to "0" hours when the hour enable pulse occurs 5 1/2 seconds before the actual time of "0" hours. The "0" hour is announced in advance of the 960 Hz tone that begins precisely at the start of the hour "0". All other hours have a binary "1" added during this 5 1/2second period.

The minute 59:55 through 59:59 is detected by logic circuitry 650 and a binary 5 is added to the 6-bit minute code. The binary code enters into the seven's and non-existent bit. The binary code at the input of the minute servo appears as "0" minutes and the minute servo system changes the minute sound head to the zero record track (o'clock track) under control of the minute enable pulse which occurs at 55 1/2seconds. For all other minutes, a binary "1"is added to each minute during this same period to advance the next minute announcement so it is heard prior to the 960 Hz marker tone.

The seconds announcements change 12 times each minute, once for each announcement cycle, and therefore no logic correction is necessary. The recording of the seconds announcements are offset by one increment.

A set of holding latches 658, 660, 662 and 664 (FIG. 10) provides the necessary memory for the servo systems. The enable inputs from FIG. 3 are supplied to latches 658-664 and the hour servo, minute servo and second servo control signals are provided to FIG. 3 as previously described. Thus, movement of the servo systems occurs only when a new binary code is applied to the latch input plus the receipt of an enable pulse from the message assembly unit as previously described.

Referring to the mechanical components of the system as illustrated in FIG. 11, the base of the machine 700 supports a flanged shaft 702 standing in a vertical position. Mounted to flange 704 on Neoprene rubber shock mounts is hysteresis synchronous motor 706 and worm gear 708 (FIG. 13). The shaft of the worm gear extends into and is secured to the rotor of the motor. The motor and worm gear operate submerged in automatic transmission fluid 710, which requires that the rotor and the inside of the motor stator be smooth, with the outside diameter of the rotor 0.020 to 0.030 inches smaller than the inside of the stator. This configuration is necessary to minimize friction. Worm gear 708 meshes with and drives a worm gear 712 that is secured to support 714 which is mounted on a bearing 716 enabling free rotation of worm gear 712 and support 714. Inserted in gear support 714 are two felt drive bushings 716 which are used as compliance filters to reduce motor and worm gear noise and vibration.

Above worm gear 712 and worm gear support 714 is metal flywheel 718 mounted on bearing 720. From the bottom of flywheel 718, two metal drive pins 722 extend down and into felt drive busings 716 to provide a rotation drive from worm gear 712. Above flywheel 718 there is a record hub 732 and second flywheel 726 that is mounted on two bearings (not shown). Inserted in the bottom of the flywheel part of record hub 732 is felt drive busing 724. From the top of first flywheel 718, metal drive pin 734 extends up and into felt drive bushings 724. This continues the rotation drive from flywheel 718 and worm gear 712. The second felt drive busing 724 is used as a second compliance filter to further reduce noise and vibration.

Using this dual compliance flutter filters with the rotating masses and the main drive motor completely submerged in transmission fluid provides viscous damping, cooling and lubrication thereby enabling production of gear driven announcement machines to be consistently constructed with wide band flutter of less than 0.05 percent.

Casing 736 encloses the internal parts of the machine. Casing 736 and flanged shaft 702 are sealed at the mating seam by two neoprene "O" rings 738 to prevent the leakage of transmission fluid. Mounted to the top of casing 736 is mounting plate 740 that is the mounting surface for modular carriage assembly 742, described below. This is also sealed at the mating seam with neoprene "O" ring 744. Casing 736 is also filled with automatic transmission fluid.

With continuing reference to FIG. 11 and with additional reference to FIG. 12, modular carriage assembly 742 comprises the following components.

There are two vertical support plates 746 and 747 mounted to base plate 748 and to top plate 750 forming a very strong box-like structure. Secured in this structure are two slide rods 752. Carriage 754 travels up and down slide rods 752 guided by two ball bushings 756 that are pressed into carriage 754. Ball bushings 756 are of the recirculating ball type and provide almost friction free linear motion.

With particular reference to FIG. 12, pivot pin 758 is mounted to carriage 754 and extends through two flange-type ball bearings (not shown) and head arm 762. The bearings and head arm 762 are held in place by retaining collar 764. This will allow free pivot motion of head arm 762 with magnetic sound head 766 mounted therein.

Precision ground ball bearing screw 768 is supported in top plate 750 by ball bearing 770 and extends downwardly through ball bearing nut 772. Screw 768 is supported in base plate 748 by ball bearing 774. From this point ball screw 768 extends down and into the rotor of servo step motor 776, with the rotor secured to the end of ball screw 768 in a permanent position. Ball screw 768 has a lead of 0.125 inches per revolution. Using this configuration the rotary motion of step motor 776 and ball screw 768 is converted to linear motion through ball nut 772 which in turn will advance carriage 754 and magnetic head assembly 762, 766, 0.125 inches for each revolution of ball screw 768 and step motor 776.

Metal optical encoder plate 776 is connected to carriage 754 by mounting bracket 778 and extends down through optical reader 780. Reader 780 is then mounted to a vertical support plate (not shown). The vertical support plate and bracket 778 are dove-tailed to allow up and down adjustment of optical reader 780. Encoder visual scale 786 is mounted to a vertical support (not shown) by a dove-tailed construction to properly align visual scale 786 with visual pointer 790 that is mounted to carriage 754.

The modular carriage assembly just described is mounted to mounting plate 792. Servo step motor 776 extends down through an opening in mounting plate 792 and is submerged in automatic transmission fluid. Two slide rods 752 extend down into two locator holes 794 in the top of mounting plate 792. This properly aligns the modular carriage assembly with magnetic record 796. The modular construction of the carriage assembly affords easy mechanical assembly to mounting plate 792 of the machine by four screws. All four modular carriage assemblies are alike and thereby interchangeable.

Magnetic record 796 is a synthetic rubber band that consists of cobalt, iron oxide and hypelon rubber. Record band 798 (FIG. 12) is cemented to the exterior surface of aluminum drum 800. The exterior surface of record band 798 is then ground to a smooth and true finish. Record drum 800 is mounted to record hub 732 and is retained in place by two record locking screws 802. There are 256 magnetic record tracks 0.03125 inches apart on magnetic record band 798. Four or more modular carriage assemblies 742 are equally spaced around record band 796 and mounted to mounting plate 792.

The exact position of a magnetic head 766 relative to record 796 is determined by magnetic detent 804 in step motor 774 and adjustment of ball screw mechanism 768, 772, the position of optical encoder 780 and the input logic code. Ball screw 768 and magnetic detent 804 determine the exact head position relative to a given magnetic record track and optical encoder 780 determines which one of the 256 track positions head 766 is at for a given logic input.

With respect to FIGS. 15A and 15B, mounted in base plate 748 of one modular carriage assembly 742 is bracket 808 containing one MRD 150 phototransistor 810 and one MLED 60 IR light emitting diode 812, to comprise light switch 244. Mounted to the bottom end of record drum 732 is interrupter blade 814 which extends down into a hook shape. This hook shape is designed for the purpose that excess silicone lubrication from record band 798 will not impair the operation of interrupter switch 244. With interrupter switch 244 mounted to record drum 800, the hook part will pass through aperture 816 in light switch 244. This system is required in order to bring the prerecorded time announcing record into exact synchronization with the TIME.

With respect to FIG. 12, silicone oil is used to lubricate the surface or recording band 798 to prevent wear of magnetic head 766. The silicone oil is applied by felt spreader 815 that is sandwiched between mounting bracket 818 and felt wick 820 and is retained in place by clamp plate 822. Felt spreader 816 and felt wick 820 extend the entire length of recording band 798 with wick 820 extending down and into reservoir 824 containing the silicone oil. Wick 820 filters and transfers the silicone oil to felt spreader 816 and will remove any excess silicone oil from the record.

Neoprene "O" rings and sealant are used at all mating seams of casing 736, flanged shaft 702 and mounting plate 792. The machine is then mounted in a leakproof drawer. A cover is mounted on the top flange of the drawer with a hole large enough to provide clearance for the modular carriage assemblies. Handles are mounted on the cover to add strength to the cover and drawer assembly and for lifting the drawer assembly. Easy access to the machine for servicing the equipment is afforded by ball bearing slides. With this mounting the machine can be rolled out of its enclosure for servicing and rolled back after servicing is completed with very little effort.

FIG. 14 illustrates a code format for the encoder that is used to provide the position feedback information for the step motor servo amplifiers as previously described. Encoder plate 848 is constructed from a chemically milled, phosphor bronze 0.020 inch plate coded for 256 positions. An 8-bit modified Gray code is cut into the plate with the two most significant bits reversed so that the plate will be structurally strong. The encoder plate illustrated in FIG. 14 is arranged to indicate temperature, from -40.degree. to 120.degree. or a number scale from 0 to 250. This encoder plate is typical of the four encoder plates needed for the system. One encoder plate indicates temperature, and the other three encoders respectively indicate hours, minutes and seconds.

An encoder plate is associated with each of encoders 116, 118, 120 and 188 shown in FIG. 3. Each of encoders 116, 118, 120 and 188 comprise the following. There are eight light emitting diodes connected in series. A light gate is mounted between the encoder plate 848 and the eight phototransistors to define a light beam width of approximately 0.010. inch. The phototransistors are connected to eight Schmitt trigger circuits and modified Gray code-to-binary converters. As previously described, the output of the converter is applied to the particular motor servo amplifier in FIG. 3 to individually position the hour, minute, second and temperature sound heads.

Telephone trunk circuits previously used for time of day and temperature announcement systems have consisted usually of a relay that indicated when an incoming call was connected to the trunk (RU). This set up a hold relay (LK) that delayed the connection of the audio and the "Ring Trip" of the central office equipment until the beginning of the next complete announcement cycle that was indicated by a CT (cut through) pulse from the announcement machine. This set up a CT relay that connected the sound and remained activated until the end of the announcement cycle. The CT relay was released by a CO (cut off) pulse from the announcement machine to restore the trunk circuit so that it could accept a new telephone call. This general type of trunk circuit such as Western Electric type No. SD 96496-2D has certain disadvantages that are overcome by the optically coupled multiple input connector trunk circuit described in FIG. 16. The advantages of the connector circuit of FIG. 16 are as follows:

1. The telephone circuit holding time required is exactly the same for the new trunk with an announcement length of 15 seconds as that required for the older concept with a 10 second announcement cycle. This is due to a reduction of the subscriber waiting time for access to the beginning of the announcement by 66 percent.

2. 100 percent solid state operation. By the use of solid state components, the speed and reliability of all switching is multiplied by a factor of 100,000. This eliminates 26 mechanical contacts and three relays from the system for each trunk line circuit used.

3. Optical coupling and isolation. This provides solid state switching, audio coupling, and accurately controlled loop current, that is constant for any type of central office regardless of the loop resistance.

4. Noiseless loop closure and disconnect due to the controlled rise and fall time when the DC path is cut-through at the beginning of the announcement and cut-off at the end of the announcement.

5. No cross talk due to transformer field stray coupling, from trunk-to-trunk. This allows announcement trunks to be very compact with no danger of cross talk problems. Cost reduction is accomplished by providing a lighter more compact unit without expensive large coupling transformers.

6. No adjustment or maintenance or replacement of relays due to wear that normally occurs in these high usage trunks.

The telephone line and its supervision controls are optically isolated from the logic and audio circuits of the TTA system. This eliminates the effect of telephone line longitudinal voltages. The trunk appears as a subscriber's telephone to the central office equipment and will operate in the place of a subscriber telephone by simply connecting the tip annd ring to terminals 870 and 871 of FIG. 16 and the other circuits of the TTA system. A subscriber dials the correct number and his line is connected to the connector terminal's phone line that is in turn connected to terminals 870 and 871. An alternating 20 Hz, 90 volt signal is superimposed on a 48 volt DC voltage (STD. Telco ringing operating practice). Resistor 872, capacitor 874, diode 876, optical coupling circuit 878, and thermistor 880 conduct. Optical coupling circuit 878 comprises light emitting diode 882 and phototransistor 884. As the phase of the 20 Hz signal changes, the conduction continues and after about 1 second the current through the diodes 876 and 882 is approximately 0.020 Amps due to the reduction of the resistance of thermistor 880 to about 2500ohms. Diode 876 simply provides a chargin path for DC blocking condenser 874 and continuity for the remainder of the circuit. Resistor 872 is aa maximum current limiting resistor. Thermistor 880 is a type 46 A1 thermistor, to allow a current of 0.020 Amps to flow after approximately one second of heating of its negative resistance. Its cold resistance is approximately 50,000.OMEGA.. The purpose of the thermistor is to prevent transient voltages from triggering the circuit when it is not in use. The half wave 0.020 Amp current flowing through optical coupling circuit 878 causes light emitting diode 882 to emit infra red light. This is optically coupled to phototransistor 884. Phototransistor 884 conducts the logic voltage at terminal 2 of flip-flop 886 to ground causing its output Q 15 to go high and output Q 14 to go low. This is a steady state signal until a ground is applied to reset terminal No. 3. Output Q 15 is connected through current limiting resistor 888 to light call waiting indicator 890. Output Q 15 is also connected to NOR gate 892. Its output is turned off to extinguish light emitting diode 894 in optical circuit 896 thereby opening the trunk supervisory circuit between terminals 897 and 898. Inverter 900 causes light emitting diode 902 in optical circuit 904 to light through resistor 906. This causes trunk supervisory terminal 897 to be grounded by phototransistor 906. Output Q 15 also connects to one input of announcement selection flip-flops 908, 910 and 912. Output Q 14 connects to the other input of announcement flip-flops 908, 910, 912.

The first CT pulse, after a new call rings up, occurs at terminals 913, 914, 915, after the JK input terminals for flip-flops 908, 910, 912 are inverted and is applied to the clock input of the associated flip-flop. For example, a high signal at terminal 913 is applied to the clock input of announcement flip-flop 908. This isolates the input of flip-flop 908 and transfers the low input to flip-flop 908 to cause output Q 11 thereof to go high when the CT pulse ends. Output Q 11 is connected to NOR gate 916 causing its output to go low. The NOR gate 916 output is connected to reset flip-flop 886. This causes output Q 15 to go low and also extinguishes light emitting diode 890. The output of NOR gate 916 is inverted by inverter 918 and is connected to one input of NOR gate 892 to provide continued supervision on terminals 897 and 898. This circuit is used as an option in some central offices. The output of NOR gate 918 is also connected to current limiting resistor 920 and light emitting diode 922 to provide the call-answered indication and is connected to output terminal 923 to provide a circuit for counting the number of calls the trunk has answered. Output Q 11 of flip-flop 908 is also connected to resistor 924 and capacitor 926 to provide a 50 millisecond delay network that causes transistor 928 to turn on within 50 milliseconds. +24 volts terminal 929 is by-passed by capacitor 930 to audio ground 931. Current flows from terminal 929 through optical circuit 932 causing light emitting diode 934 to light. The current continues through current limiting resistor 936 through transistor 928 and resistance 938 to ground. This current is modulated by the audio output of channel 1 applied to terminal 939 through divider 940 and 938 to ground. The CT pulse of channel 1 occurred just before the start of the announcement at input 913. The resistor 924 and capacitor 926 network causes a smooth 50 millisecond delay in the turn on and the turn off time of light emitting diode 934. The outputs Q 15 of flip-flop 910 and output Q 11 of flip-flops 912 remain low because flip-flop 886 was reset by flip-flop 908 through NOR gate 916 before CT-2 or CT-3 occurred at terminals 870, 871. Therefore, transistors 942 and 944 remain nonconductive during the remainder of the cycle.

When light emitting diode 934 is turned on, phototransistor 946 becomes condutive. This turns on transistor 948 and the bias developed across resistor 950 turns on transistor 952. This in turn begins to turn off phototransistor 946. A 22 ma steady state current is soon reached by the DC feedback that stabilizes the operating point so that transistor 948 is now in a linear portion of its operating characteristics. The resistor 954, capacitor 956 network is adjusted to generate a proper A.C. feedback to provde a constant distortion free output over a wide range of central office supply voltage. Diode bridge 958 consisting of diodes 959, 960, 961 and 962 provides the proper polarity DC voltage at all times to supply transistor 948.

The optical coupler and the circuits it controls serves to complete the central office loop and maintain it at 22 ma. The signal at terminal 914 seizes the loop with a 50 MS rise time, and a 50 MS release time so that no pop will occur. The signal at terminal 915 isolates and couples the audio from the proper channel to the telephone line for a complete announcement beginning with a subscribers wait of no more than 5 seconds with a three channel 15 second cycle system.

The next CT pulse occurs at input 913, shifts out the low that was applied to the input of flip-flop 908, and restores the circuit to normal, extinguishing light emitting diode 934 and ending the cycle. Also light emitting diode 902 in optical circuit 904 is extinguished as well as light emitting diode 850, the light emitting diode 894 is turned on.

The other two channels operate exactly as the first depending only when the new call connects to the input terminals 870 and 871. The selector level, and other multiple answering trunks work in a similar manner. These circuits allow the full use of the TTA system to answer a new group of calls each 5 seconds.

An exemplary embodiment of the necessary analog gating, preamplifier and amplifier circuitry is illustrated in FIGS. 17 and 18. Preamplifier 970 receives an input from the temperature head in FIG. 3 and provides an output at terminal 975 to terminal 976 of FIG. 17. Preamplifier 971 receives an input from the hour head in FIG. 3 and provides an output on terminal 977 to terminal 978 in FIG. 18. Preamplifier 972 receives an input from the minute head of FIG. 3 and provides an output at terminal 979 to terminal 980 of FIG. 18. Preamplifier 973 receives the seconds input from the seconds head of FIG. 3 and provides an output at terminal 981 to terminal 982 of FIG. 18. Preamplifier 974 receives an input from the message head of FIG. 3 and provides an output at terminal 983 to terminal 984 of FIG. 18. The power and ground connections illustrated with respect to preamplifier 970 are also made with respect to preamplifiers 971, 972, 973 and 974. The preamplifiers 970-974 are conventional and are deisgned to receive a 0.0005 volts RMS input signal which is amplified to a 0.5 RMS output and the noise distortion is minus 60 Db at 0.25 percent.

With respect to FIG. 17, the audio message input at terminal 984 is amplified by field effect transistor 985; the seconds input at terminal 982 is amplified by transistor 986; the minute input at terminal 980 is amplified by field effect transistor 987; the hour input at terminal 978 is amplified by field effect transistor 988; the temperature input at terminal 976 is amplified by field effect transistor 989; and the 960 Hz sine wave input at terminal 990, which is received from FIG. 6, is amplified by field effect transistor 991. Additionally, each of the field effect amplifiers is controlled by a logic gate. In FIG. 17 only the connections for channel 1 are shown and the connections for the remaining channels 2 and 3 are similar. The logic message from terminal 421 of FIG. 7 is applied to gate field effect transistor 985 through gate 992. The logic seconds signal from terminal 445 of FIG. 7 controls the amplification of field effect transistor 986 through gate 993. The minutes input from terminal 444 of FIG. 7 controls gate 994 of amplifier 97. The hour logic input from terminal 417 of FIG. 17 actuates gate 995 of amplifier 988. The temperature logic input from terminal 431 of FIG. 7 controls gate 996 of amplifier 989. Finally, the logic marker tone at terminal 423 of FIG. 7 controls gate 997 to actuate amplifier 991. The outputs of amplifiers 985, 986, 987, 988, 989, and 991 are connected to a common bus 998 and the audio gain is controlled by potentiometer 999, which controls the input to amplifier 1000. Equalization of the signal is provided by equalization circuit 1002. The audio output is conneted to terminal 939 of FIG. 16.

FIG. 19 represents an exemplary embodiment of the 960 Hz active filter which extends the sine wave signal at its input 1004 in a conventional manner to provide a 960 Hz extended output for the marker tone at output 1006. Active filter 1007 comprises a linear operational amplifier which is designed and operated in a manner known to those skilled in the art. Potentiometer 1008 provides a means for adjusting the output for the maximum sine wave output and potentiometer 1010 provides a level control. The output at terminal 1006 is supplied to terminal 990 of FIG. 17.

While not illustrated in the drawings, it is to be understood that the programming of the message output may be greatly simplified by mechanically connecting the message and seconds sound heads together so that the message head moves with the seconds head. This, of course, restricts the message output to that corresponding to the particular seconds announcement. However, the programming can be suitably modified so that the message and sound head can be separately driven.

It is also further understood that the various electrical components, such as the counters, dividers, logic gates, amplifiers, etc. of the embodiments of the foregoing description are not of unique design in and of themselves, but are conventional elements well known to those having skill in the art to which this invention is directed.

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