Patent GB-1270813-A (GB)
Title: Telephone answering devices
Inventor: MULLER WILLY
IPC: H04M1/652
Filed: 1969-04-29
Abstract: 1,270,813 Substation equipment; automatic gain control. W. MULLER. 29 April, 1969 [31 Dec., 1968], No. 21864/69. Headings H4K and H4R. [Also in Divisions G4-G6] A telephone answering device includes a first magnetic recording unit which plays back prerecorded messages to the caller and a second separate magnetic recording unit for recording a caller's message which latter record can be remotely replayed on receipt of the correct code. The device can be operated in five different modes which are selected by operation of switch 15. Switch 15 can be moved freely between positions I and II but requires the operation of a lock to move into position III when it is again free to move to position IV but operation of a lock is again required to move to position V. The provision of the lock ensures that the recorded messages cannot be replayed to unauthorized people or erased in error. Construction.-The device includes first answering recorder 100 which is similar to that shown in Specification 1.270,814 except that it is provided with two recording heads TK2 and TK3 and two erase heads LK2, LK3 and also two sequencing contact track discs. In operation it differs from the apparatus of the copending application in that it gives both an opening and closing announcement. The caller's message is recorded on a second recorder 200 which uses a cassette or cartridge of tape mounted on take up spindles 202, 203. Normal speed forward drive and fast reverse drive are provided by the operation of electromagnets MB and RM respectively (electromagnet RM is shown in Fig. 10). When electromagnet MB is energized pinch wheel 211 is pressed against capstan 208 to drive the tape past erase and recording heads LK1, TK1 and spindle 203 is rotated through a slipping clutch mechanism. With fast reverse operation spindle 202 is driven. Levers 218 and 246 are attached to a brake pad which contacts spindle 203 unless one of the electromagnets is energized. Also driven from spindle  202 through step down gearing is a tape position marker comprising a wheel 305 and a second wheel 307 coupled through a slipping clutch and having projections 312, 308 respectively. The gearing is such that 350 degrees revolution of wheel 305 corresponds to the length of tape in the cassette and the separation between projections 312 and 308 represents the amount of tape used to record messages. The tape can thus be run to the start when contact ak opens or to the end of recording when projection 308 opens contact mk. Operation.-The device can be used either as a telephone answering device or as a tape recorder and the various operations necessary to these functions are selected by means of switch 15 and pushbuttons 8, 9, 10, 11, these last controlling stopping, starting, rewind and erase when the device is used as a tape recorder. With selector switch 15 at position I the device is connected to telephone line Ta Tb and a ringing signal will be detected in call circuit 507 to cause pick up of relay AR and start the drive motors M1 M2. The recorded text is replayed to the caller from head TK2 through amplifier 509 and the hybrid TR2, TR3. The electromagnet MB is energized to start second recorder 200 and the caller's message passes through filter 511 and amplifier 510 to recording head TK1. This connection remains for the set time in circuit 513 or until the speaker pauses for 6-8 seconds when speak relay HR opens and the closure message is transmitted from head TK2. The device resets itself to the initial condition awaiting a further call. The caller can cause the device to replay any message previously recorded by intoning a vowel sound immediately the opening announcement has been made. This sound passes through filter 511 causing a code relay to pull up and connect head TK3 to the lines through playback amplifier 509. Code numbers are sent to the caller. The code is set by operating the pushbuttons numbered 1-4 on the rear of the device and requires that a vowel sound is intoned by the caller after the number of the respective pushbutton is heard. On receipt of the correct code the caller is instructed to wait while the tape is rewound and the messages are then played back. After all the messages have been repeated the tape can be erased or not depending again on the receipt of a code and the device will reset itself to receive further messages. To record the answering text the microphone is used in socket BU2 on the back of the machine but for tape recorder operation socket BU1 is used. To prevent overloading the tape, amplifier 508 is provided with an automatic gain control operating by shunting the input of the second stage of the three stage transistor amplifier, Fig. 19 (not shown). The timing switch 513 is a multivibrator using a unijunction transistor which stops the recording after a set period has elapsed and a similar circuit is used in the light control 512 which indicates that a message has been recorded. The speech switch 511, 510 employs transistors which convert sinusoidal speech signals into pulses and operates relay HR, Fig. 18 (not shown).