Light emitter photodiode optical isolator - uses piezoelectric ceramic filter elements for control

摘要

A light emitter (12) is modulated at a frequency set by a piezoelectric ceramic filter element (4) connected around a transistor (8) to form an oscillator. Suitable amplification is placed between this and the emitter. A photodiode (22) receives beam (16) and uses the signals to control a relay (42). Some of the amplifiers are tuned by similar piezoelectric ceramic filters of the same frequency to improve the noise immunity and stability. The signal is detected and further amplified. Preferably the photodiode (22) is made of silicon and the frequency of operation is high enough for the diode noise to be less than 1/10th of the dc value.