Patent GB-1351868-A (GB)
Title: Proximity switch
IPC: H03K17/96
Filed: 1971-04-19
Abstract: 1351868 Transistor oscillators and bi-stable circuits ADOLPHE FELLER SA 19 April 1971 [3 Feb 1970 4 Jan 1971] 20836/71 Heading H3T [Also in Divisions H1 and G1] A relay is operated when a transistor oscillator is started by touching an electrode in the feedback circuit, the consequential impedance decrease due to the human contact in the feedback circuit being sufficient to initiate the generation of oscillation. A Hartley oscillator is shown in Fig. 1 in which a transistor 1 has a feedback circuit comprising an oscillatory circuit L1, C in the collector circuit coupled to a feedback coil L2. Normally the transistor is cut off by a bias potential from a potential divider r p , r b , but when electrode P1 is touched the feedback circuit is completed through the human body and oscillation commences; the increased transistor current operating a relay 9. Feedback is regulated by a variable resistor r a , and three possible operating conditions are available depending on the resistance setting. These conditions are, starting from a low resistance value r a  and increasing, that oscillations occur only during the time P1 is touched (astable operation), that touching P1 commences oscillation which continues until P2 is touched (bi-stable operation), and that permanent oscillations are terminated during the time P2 is touched (inverse astable operation.). The resistor r a  may optionally be connected in series with the coil L2, Figs. 1a, 1b (not shown). In a modification, Fig. 3 (not shown), the coil L2 is tuned by condenser C instead of L1, and the degree of feedback is determined by varying the mutual coupling, a suitable construction being disclosed (see Division H1). An arrangement is described, Fig. 5, for controlling a circuit breaker CT using an astable touch operated oscillator TE and associated relay R, the arrangement being energized from an A.C. supply S1, S7, which is rectified at D31 for energizing the oscillator, a Zener diode D32 being provided for limiting the rectified voltage. When the oscillator TE is made operative by touch, relay R pulls up and permits CT to operate by shorting out R31, D31 and a storage capacitor 31. Thereafter the oscillator remains operative for a short time by using the charge stored in capacitor 31, the relay then falling back and re-establishing the initial circuit condition when the generation of oscillations cease. In an alternative arrangement, Fig. 6, the oscillator is energized from a full wave rectifier DP, and when oscillation is initiated causes relay R to short out a resistor R40. Current from A.C. source S1, S2 is then sufficient to operate circuit breaker CT and maintain oscillation of TE. A modification, Fig. 7 (not shown), uses a series-connected centretapped transformer and a rectifier pair to provide full wave rectification. A two-way switching system may be formed by using two bistable operation devices of the Fig. 3 type each having "on" and "off" electrodes (P1), (P2) and (P<SP>1</SP>1), (P<SP>1</SP>2), respectively, Fig. 8 (not shown). Each device controls a respective winding of a circuit breaker, the two windings being arranged so as to act in opposition. Another system, Fig. 9A (not shown) uses several bi-stable operation devices (17), (18), (19) with their relays (20), (21), (22) to control a single circuit breaker (16). A single relay is used in a modification of Fig. 9A, Fig. 9B (not shown).