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 simple MW radio does not need an external antenna to pick up local stations. It was found in a...
This is a typical ohmmeter circuit with 50 uA analog instrument. The circuit was found in Radio...
This very simple circuit turns on an LED when an object interrupts the light that falls on the...