This interesting circuit found in American documentation generates a busy signal, without you having to take the phone off the hook if you do not want to answer. The components used are common.
This receiver receives signals from the VHF band with earpiece or application in a power stage. The...
Originally created to power an 80's RTTY printer, this circuit can be used in other applications. The...
This circuit is from a Popular Electronics of the 90's. Any power MOSFET can be used. The circuit...