We found this circuit in the magazine Eletcronics Now of July 1994. The power supply is according to the relay and the transistor can be any general purpose one.
This circuit uses components that are still common despite being from 1995 documentation. The circuit can...
This filter was found in Delco's 1965 documentation. It can be implemented with modern components...
This circuit was found in an old publication and can be adapted for use with modern...