GB1312942A - Electronic anti-theft device - Google Patents

Abstract

1312942 Releasable fastenings M NICOLA and E LUCIANO 2 April 1970 [2 April 1970] 15754/70 Heading E2A [Also in Divisions G4 H1 and H2] In a key-operated switching device for controlling an electrical latch on a door or a safe or for controlling a vehicle, the key 22 comprises an insulating body 20 carrying a plurality of contacts 31..39 connected in a predetermined manner and cooperating with a socket 41 having blocking means 42 defining first and second positions for the key 22 in the socket 41, the electrical connections made to the contacts 31..39 being different in the first and second positions such that in the first position a door is capable of being opened and an alarm circuit rendered inoperative whilst in the second position the door is locked and an alarm circuit is capable of being operative. As described, the first position is defined by a recess 40 in key 22 being engaged by a spring 42 in the socket 41 so that contacts 31..38 are respectively engaged by contacts 1a..8a, while the first position is defined by full insertion of the key 22 so that contacts 9a, 10a are additionally bridged by contact 39. Identibcation of correct key. In the particular key shown, contacts 31, 36, 37 and 38 are joined by a printed circuit, whilst contacts 32..35 are isolated. Fig. 4 shows a logic system for operating the lock-controlling relay RL2 and the alarm relay RL1. The circuit receives power from a battery connected between terminals F and H only if contacts 9 and 10 on the socket 31 are bridged by a contact 39 when the key 20 is in its fully home position or if relay RL2 is energised by a bistable pair of transistors Tr8, Tr9. Transistor Tr1 and diodes D1..D3 sense the key presence by supplying a "1" at A when the key is inserted. Transistor Tr2 and diodes D5..D7 supply a "1" at B if the correct contacts (36, 37, 38) are connected together. Transistor Tr3 supplies a "0" at C when one of the isolated contacts 32..35 are connected. The three logic signals at A, B, C turn on transistor Tr5 which inhibits Tr4 and thus prevents operation of the alarm relay RL1, but the insertion of an incorrect key or the opening of door switches connected at L will set off the alarm by energising RL1, which is then held energised by feedback via Tr7 and D9 but may be released by the insertion of the correct key. Locking door and setting alarm. The door is locked by inserting the key 20 fully into the socket 41 and then withdrawing the key, this action allowing a pulse from signal B to be passed via a capacitor M to set bistable Tr8, Tr9 so that RL2 is energised, contacts 47 of which retain the power to the logic circuit when the key is withdrawn. Unlocking door and inhibiting alarm. The lock is released and the alarm inhibited by insertion of the key into the first position (up to the stop 42) when bistable Tr8, Tr9 will be reset, releasing RL2. Modifications. The key may operate further devices by rotary movement. In a car, circuit G may break the supply to the ignition coil when the alarm is set.