Patent GB-1177931-A (GB)
Title: Interrogation Apparatus
Inventor: WHITE LAURENCE GEORGE
IPC: H04M1/652
Filed: 1965-11-30
Abstract: 1,177,931. Telephone answering machines. SHIPTON ELECTRONICS Ltd. 17 Feb., 1967 [30 Nov., 1965], No. 50860/66. Heading H4K. A telephone answering machine containing messages recorded in a subscriber's absence is interrogated by a caller in response to a code comprising a number of groups of bursts of speech or noise, each group being sent by the caller upon command from the machine. The command signals from the machine each consist of a burst of tone with the tone burst demanding the first group of the code being longer than the other equal length tone bursts pertaining to the remaining groups. The whole sequence of tone bursts is sent to the caller a short time after he has been invited to record a message and is repeated whilst awaiting him to transmit the code. The bursts of the code may be made by the caller speaking digits in sequence, the number of bursts in each group being counted by the machine which responds to the correct code by playing the recorded messages over the telephone line. If the caller begins a message once the command signals have started, the reception of continuous speech by the machine inhibits further command signals. After hearing the messages the caller may send the interrogation code again and have the messages erased. Fig. 1 shows in its upper half circuitry for generating the command signals and in its lower half circuitry for receiving the speech or noise bursts, counting them and recognizing their correct number and sequence. A pulse generator 1 drives a 1À5 kc/s. oscillator 2 to produce bursts of tone at intervals of one second and also drives upon the back edge of a pulse a two-stage binary counter 3 having a decimal output on wires 16-19. Wire 16 is coupled via TR5 to the pulse generator to vary its tonic constant and make every fourth pulse and therefore burst of tone of longer duration than the other three. Their sequence of four tone bursts provides the command signals. Speech or noise bursts sent by a caller are received by a circuit 4 which provides a pulse for every burst and which pulses are counted by a threestage binary counter 5. Whilst speech or noise signals are being received an output over lead 22 and diode D3 inhibits the pulse generator 1 so preventing the sending of the next command signal until all the bursts of a group have been received. The count for a group of bursts appears in decimal form on wires 23 which are multipled over selector switches S1 to S4. The wipers of the selector switches are set to the number of pulses of one of the groups and are each connected to a particular one of the AND gates 6-9. These gates each receive in sequence an input over wires 16-19 in accordance with the command signals. If the count of speech bursts for a particular command signal is correct, as determined by the switch S, the particular gate is opened to step on a threestage binary counter 10. If at the end of the code this counter has reached a predetermined count the machine responds by playing back the messages. The speech burst counter 5 and AND gates 6-9 are reset after each group of bursts by the leading edge of the pulses from generator 1. The counter 10 is reset at the end of a sequence by the back edge of the long pulse. If an incorrect code is sent counter 10 does not reach the predetermined count and the command signals are sent again. The operation of the machine upon successful interrogation is controlled by a number of bistable circuits (Fig. 3, not shown) which cause the tape to rewind to the stop foil at the tape beginning and to then replay the messages over the line. At the end of the replay the tape is wound a little further, stopped and the machine reverted to stand-by ready to record further messages. If the caller hangs up the machine shuts down in response to dial tone. However if the caller resends the interrogation code to erase the messages the machine informs the caller that it is about to disconnect itself from the line and after doing so, rewinds the tape to erase the recording. The machine now gives itself a dummy call to advance the recording well beyond the stop foil of the tape. If the machine is faulty and fails to record a transmitted message it disconnects itself from the line, informing the caller as it does so.