Patent GB-1408899-A (GB)
Title: Automatic telephone call answering machine
Inventor: MULLER W
IPC: H04M1/65
Filed: 1972-11-28
Abstract: 1408899 Substation equipment W MULLER 28 Nov 1972 [31 July 1972] 54964/72 Heading H4K In a telephone answering machine, the control circuitry operates on a digital basis. The control logic takes the form of an integrated circuit pack. Each component such as a relay, motor and signal lamp is connected in series with the emitter/collector path of a transistor which is turned-on and -off by zero or positive level signals applied to its base. The machine is formed as a plinth unit for a telephone subset (Fig. 1, not shown) and utilizes magnetic cassettes whose movements are controlled by push buttons located on the front panel of the plinth. The general arrangement shown in Fig. 2 uses a convention that boxed references, e.g. HF, indicate a (positive level) digital control signal supplied from the logic whereas encircled references, e.g. AS, indicate a (zero level) digital signal supplied to the logic.  Recording an announcement.-A function switch is set to the relevant position thereby lighting a pilot lamp and applying a start condition to the logic which responds by enabling relays K5, K6 (of corresponding contacts in Fig. 2). A microphone is thereby connected via preamp 32, and main amplifier 31 to a record/ play-back head AW1 associated with an announcement tape which is moved forward by depression of a control push button on the machine. Unit 40 provides an erase signal to erase head LK1 and a premagnetization signal via capacitor 43 to record head AW1. When the owner has made his announcement he releases the microphone speech switch but not the control push button thereby permitting the logic to enable an active filter unit 33 to impress a 200 Hz time on the recording tape. After say 6 seconds, the owner makes a final announcement, following which the tone is again recorded until the tape reaches its end whereupon a metal insert thereon bridges contacts that cause the tape to be rewound. The control push button is released. Rewind of the tape could be effected by manual intervention. Replaying the announcement.-The function switch is set appropriately whereby the record head AW1 is connected via the amplifiers to a loudspeaker 37 whose power amplifier 36 is now enabled from the logic. Answering an incoming call and recording an incoming message.-In response to ringing current, detector 27 enables the logic which actuates relay K1 to loop the line, relay K2 to connect the line to the machine via transformer 23, and K3 to connect the output of amplifier 31 to the line. The recorded announcement is replayed by head AW1 whereafter the logic permits filter 33 and detector 38 to recognize the recorded tone which provides a 6 second grace period during which the caller is expected to start talking. The announcement tape is stopped while speech occurs. Relays K6, K8, K4 are energized and K3 de-energized to connect the line to message recording head AW2. Speech detector 46 monitors the line for presence of speech and enables the logic following the absence thereof for a preset time. The logic is also enabled if a break in the recording tape is identified or if an overall system timer times out. In any case head AW1 is reconnected to line for the final announcement following which the occurrence of the second prerecorded tone causes the logic to restore the machine to rest. The announcement tape may be rewound by the logic or by its contact bridging insert. Replaying messages.-The function switch is set so that the logic enables K8 thereby connecting the head AW2 to the loudspeaker. General.-The use of transistorized differentiatiors and integrators in the ringing and speech detector circuits is suggested. The various potentiometers and variable impedances shown on the drawing are set to provide a constant recording level. Pilot lamps to indicate that the machine is connected to line, contains an incoming message and is prepared to record an announcement message are utilized.