This circuit was found in the Electronics Experimenter Handbook from 1991. The sensor is a diode and the circuit has a relay according to the voltage used in the supply.
This circuit can be used in PLL, frequency synthesizer in FM and VHF receivers, reducing a...
We found this circuit in an old documentation. Transistor can be BC548 and relay according to...
This is a typical 3 ½ digit TTL counter. We found it in the September 1973 issue of Radio...