Abstract: A transducer for optically detecting a cyclic phenomenon of variable frequency and supplying an electric signal corresponding to the frequency, comprises a light source for illuminating the site of the phenomenon and a detector for detecting variations in the level of light reflected from the site of the phenomenon and providing the required electric signal, the detector being a semiconductor opto-electronic cell and the light source being positioned within the detector.

Abstract: A photo-voltaic hetero-junction is formed by chemical conversion of surface regions of a sheet of one conductivity type into material of a second conductivity type, the areas which are not to be converted being covered by a developed photo-resist layer which has previously been exposed to light through a mask. Electrical contacts are deposited on the regions of the second type and contacts to the material of the first type are formed by a layer deposited on a substrate under the sheet of material of the first type. This deposited layer of electrically-conductive material can also form the mask for initial exposure of the photo-resist layer.