This very simple circuit uses a phototransistor and a very sensitive relay (reed type) being used over short distances with a lens system. The circuit is from a 1967 Japanese publication.
This 1/2 hertz high selectivity filter was found in the December 1990 issue of Radio Electronics...
The frequency in this circuit is adjusted by P1 and given by C1. Short pulses, as the ones...
This Hartley telegraphy oscillator operates with the transmitter signal generating a tone in a...