Transducers

Claim 1

A transducer for detecting heartbeats and supplying an output signal in dependence thereon with a frequency component of the output signal corresponding to a heartbeat rate to be detected, said transducer comprising a light emitting diode and a planar opto-electronic detector which is a photo-conductive cell encircling said light emiting diode and which comprises an electrically insulating substrate, an insulating film on said substrate, a photo-voltaic PN junction on the surface of said insulating film comprising a layer of cadmium sulfide and an annular disc of cuprous sulfide on the surface of said layer of cadmium sulfide to provide a light sensitive surface layer, first and second output terminals, conductor means connecting each of said output terminals to a respective one of said layers, the transducer adapted to be mounted on a watch case component means positionable adjacent the skin of a user with the light emitting diode facing the skin of the user to emit light thereagainst being energizable by a periodic signal from a source contained in said watch case component means, the light emitting diode being positioned when in use to emit light toward a surface of skin tissue of a user to transilluminate said surface of skin tissue to cause the surface of skin tissue to emit light and the opto-electronic detector encircling said light emitting diode so as to be positioned in close proximity to said surface of skin tissue so that the majority of light originating from said light emitting diode emitted from said surface of skin tissue is directed into said opto-electronic detector which detects variations in the reflected light level from said surface of skin tissue and provides said output signal to said first and second output terminals in response to changes in arterial blood flow.