This circuit is from a 1968 documentation using one of the first integrated circuits available at the time, the TAA370. The circuit is powered by 1.3 V using a 200 ohm handset.
This circuit makes use of a low impedance microphone. The relay is according to the supply voltage...
This is a typical RF oscillator configuration found in a 1980s documentation. The frequency...
We find this circuit in an old American documentation from the 80's. The integrated is from the...