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.
The transistors in this circuit can be the BC548 and a small speaker serves as a microphone. The...
This circuit generates signals whose frequency depends on C1 and C2. JFETs are common types like...
We found this small FM transmitter in a 1980 publication. What sets it apart from traditional...