This circuit of a 1964 Electronic Design uses a photodiode from the time. Modern equivalent can be used. The standby current is 1.2 mA.
This circuit takes advantage of the inductance of the phone in the resonant circuit. The circuit is...
We found this sensitive high input impedance voltage amplifier in the November 1970 Radio...
This circuit detects when a powered circuit suffers a malfunction, lighting an LED. The supply...