Patent GB-852198-A (GB)
Title: Improvements in or relating to apparatus for sending signals indicative of the values of coins inserted into a coin operated telephone instrument, to a control device inan automatic telephone exchange
IPC: H04M17/02
Filed: 1958-10-24
Abstract: 852,198. Automatic exchange systems. TELEFONAKTIEBOLAGET L. M. ERICSSON. Oct 24, 1958-[Nov. 6, 1967], No. 34158/58. Class 40 (4). In a sub-set like that described in Specification 790,442 in which digit keys control the insertion< of.eharacteristic impedances into a resonant circuit to produce voice frequency damped oscillations which are fed to the exchange, the impedances may also be inserted into the resonant circuit under control of coin contacts to signal the value of inserted coins to the exchange, means being provided to prevent coin signals-being simulated by depression of the digit keys. When the caller takes down his hand-set the closure of cradle contacts K closes the loop and, as is described in the abovementioned Specification, equipment (not shown) at the exchange reverses the normal polarity (plus on La) on the line. The rectifier LI is thus blocked and condenser C1 is charged. Depression of one of the digit keys P1 to PO inserts the relevant part of inductance PC into a resonant circuit including C1 and C3 and the resulting damped oscillation produces an alternating potential across C1 of a frequency corresponding to the digit keyed, whereby a voice-frequency receiver at the exchange responds. The call is set up in the usual way and on the reply of the called party the polarity on the calling line is restored as described in the abovementioned Specification. In addition operation of the called party's feed relay R4 brings up R5 which operates R1 to connect up the coin signal receiver Tm. Relay R1 also brings up R2 which reverses the polarity on the calling line, whereupcn the progressing magnet FM in the coin box equipment MT is operated. The progressing lever FA is thus rotated anticlockwise to allow a coin to drop into engagement with the coin contact 1, 2 or 3 relevant to the coin concerned. FA also renders the digit keys P1 to P0 ineffective. Closure of the coin contact concerned completes the resonant circuit forthe frequency indicative, of the coin value and the corresponding receiving circuit A, ,B or C in the exchange responds, bringing up relay RA, RB or RC, respectively. Operation of this relay releases R5, whereupon R1. falls away, .thus disconnecting the coin signal receiver Tm, is . followed by- R2 whichrestores the polarity on the calling line. In the exchange, reception of the wanted, number results in the operation of one of the three rate relay, RI, RII RIII which connects up the relevant one of three impulsing cams KI, KII, KIII the impulses from which step the wipers of a,timing switch Vk. Segments on the lower bank of, Vk, provide for the holding of the operated relay RA, BB or RC for the period corresponding to the value of the coin inserted, and the wiring of the upper bank ensures that one step before this period elapses a buzzer Su . is energized to signal to the caller that the period paid for is about to elapse. The operated.relay RA, RB or RC is then released, and operation of the restoring magnet RE over off-normal contacts HL restores switch Vk, to the home posi-, tion. Relays R5, R1 and R2 are then reoperated and the signal corresponding to any further coin inserted is received. If no further coin is inserted the connection is released after a delay period. As will be seen from the above description the progressing magnet operates to the second reversal of polarity on the line. One embodiment operating in this manner is shown . in Fig. 2. The first reversal which occurs when the caller takes down his hand-set operates magnet Z1 via rectifier Lil whereupon the mercury switch S1 is rocked into its dotted position b<SP>1</SP> to connect up Z2. Restoration of the polarity when the called party answers operates Z2 via Li2 whereupon mercury switch S2 is rocked into its dotted position b to connect up Z3 which is operated via Li3 by the second reversal (effected by relay R2). Magnet Z3 rotates. the progressing arm FA. A second-em- - bodiment having only one magnet with mechanical linkages between it and FA, is described with reference to Fig. 3 (not shown).