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.
Found on a 1969 EDN this circuit switches a current from a digital control signal. The impedance...
This low-current power supply was found in the April 1973 issue of Radio Electronics magazine. The circuit...
The idea of this circuit from a 1960 publication is simple: we can switch the transistor being...