GB1418318A - Keyboard - Google Patents

Abstract

1418318 Photo-electric switch NATIONAL RESEARCH DEVELOPMENT CORP 11 Sept 1973 [22 Sept 1972] 43965/72 Heading G1A [Also in Division G4] The invention relates to a keyboard utilizing photo-electric switches constructed with light pipes. In the switch construction of Fig. 1, an illumination pipe 10 is surrounded by six receiver pipes 11, 14 feeding one or more photo-detectors. The switch is actuated by a spring biased push button 18 having a reflective surface 17. The switch construction can be such that the surface moves either (a) from a position at which it reflects a maximum amount of light to one at which it cuts off light completely (i.e. substantially abutting the ends of the pipes) or (b) from a position further away than said maximum reflection position, to said maximum reflection position. In Fig. 4, a spring-biased member 33 moves from a position (as shown) where it substantially cuts off reflection of light due to a blackened surface, to one in which a reflector 35 in recess 34 into position to actuate the switch. Scratching of light pipe ends is prevented by recessing the pipes. The central transmitter pipe is here associated with nine peripheral receiver pipes, one of which may serve to issue a "ready" signal to a logic circuit. In Fig. 6, the presence of a finger operates the switch, by reflection of light. Obscuration of the pipe ends is prevented by shoulder 42. Switch operation by ambient light in the absence of a finger may be prevented by rendering it sensitive only to modulated light from a half wave rectified mains supplied source. In Fig. 7 (not shown), a cooling arrangement is described for a tungsten filament lamp enclosed in a metal block into which the ends of transmitter bundles are introduced. In Figs. 8, 9, (not shown), the use of the switches in a keyborad is described (see Division G4), each key feeding a unique plurality of detectors, which latter may be provided with a lens to focus light from a plurality of pipes on to it. Alternatively, each detector may be made up of a plurality of small units whose outputs are combined.