Patent GB-803513-A (GB)
Title: Improvements in or relating to switching arrangements
Inventor: O'DWYER MARTIN THOMAS
IPC: H04M1/65
Filed: 1954-12-06
Abstract: 803,513. Switching systems. PYE, Ltd. Dec. 6, 1955 [Dec. 6, 1954], No. 35248/54. Class 38(4). [Also in Group XXXIX] In a telephone answering machine which besides sending a message to a caller invites him to record a message and comprises an electrically-driven stepping switch for controlling the sequence of operations, the switch is stepped on the completion of one operation to condition a circuit for the next operation and a circuit including a time constant network is provided through which the stepping of the switch is effected if, due to a failure, the switch is not stepped on the completion of the operation. A twelve-position rotary switch S2A-T, Fig. 1, which is stepped by solenoid L1, may be driven automatically from the D.C. supply by a relay CC or manually through a switch S5. The message for a caller is recorded by the subscriber on an endless tape in amplifier and recorder unit 2 with a system switch S1 in the " record " position. The switch S2 is then moved to its second position by the operation of push-button switch S5, to start tape motor M1 and is subsequently stepped automatically to position 3, at which H.T. is applied to the unit and an indication is given on lamp SL1 that recording may commence by relay CC which is operated through switch section S2J after a delay of 1 second. A switch S4 operated by the tape after a predetermined time steps switch S2 to its fourth position where SL1 glows more brightly to indicate that " please speak now " should be recorded. Local reproduction of the recorded message may be obtained in the " playback " position of the system switch, and interlocking is provided between units 2 and 3 to render the machine inoperative to a call during such recording and reproducing. In response to a call, relay A, which is in series with the telephone bell and is in consequence energized by ringing current, operates relay CC after a delay determined by condenser C3, and switch S2 is stepped to position 2 where tape motor M1 is energized. After 10 seconds delay due to condenser C1 and resistor R1, valve V1 is rendered conductive and relay CC is again energized to step switch S2 to position 3. Relay B is energized to connect the machine to line and the motor M2 of the main recorder unit 3 is energized. H.T. is applied to unit 2 and condenser C4, and the pre-recorded message is transmitted. The switch is driven to position 4 by the reoperation by a tape switch S4 of relay CC or in the event of its failure to operate the circuit of relay CC through valve V1 1 is rendered conductive after a delay of one minute produced by circuit R3, C1. H.T. is as a result applied to unit 3, the main recording tape is driven, and the caller is invited to speak. A " call received " lamp SL3 is lit by a relay D which is operated through switch sections S20 and S1E and is held until switch S8 is opened when the message is reproduced by the subscriber. The invitation to speak is extended also to a monitoring unit 4 (see also Fig. 4), which includes a speech filter F1 and a dialling tone filter F2, and develops a cut-off bias on the grid of V12 which, when HT2 is connected in position 5 of switch S2, persists for a short period of, say, 5 seconds to prevent the switching off of the machine by relay CC as a result of hesitancy on the part of the caller. Relay CC is subsequently held by the caller's speech until valve V12 is rendered conductive at its cessation and switch S2 is automatically " homed." When used with a telephone connected to an automatic exchange the reappearance of dialling tone on the line clears down the machine. The machine is also disconnected by relay B during a power failure or by a switch S7 which may be operated by a feeler on the tape if insufficient recording time is available to a caller. In the record-playback unit 2 which is described with reference to Fig. 2 (not shown), the amplifier is switched by the system switch to serve for both recording and reproducing and the microphone is used also as a reproducer. A dual purpose amplifier for the main recorder which uses the record H.F. bias stage as an audio output stage during reproduction is described with reference to Fig. 3 (not shown).