Abstract: An evaluation circuit for use with electronic system which utilizes a plurality of individual transmitters of light, a like plurality of individual receivers of light, and a like plurality of light conducting paths. Each transmitter is connected to its corresponding receiver by a corresponding path so that the light emitted by any transmitter can only impinge upon the corresponding receiver. The light emitted is in the form of pulses. The transmitters are selectively actuated and deactuated in selected format by a multiplexer. The corresponding receivers are synchronized to respond in the same format by a demultiplexer whereby when the system functions properly each receiver will receive and respond only to the light pulse emitted by the corresponding transmitter. In the circuit, a measuring operation is initiated in which each transmitter-receiver pair is individually actuated in a selected sequence.