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 variable power supply circuit was found in a German publication from the 1980s. The circuit is...
This simple circuit for switching RF signals was found in an RF Design from the 90s. The circuit...
We found this circuit in a 1983 English magazine, but it can be easily assembled with the BC548 or...