Poptronics recommends this circuit for use in the car when the headlights are left on. The circuit uses a sensitive relay with contact current according to the headlights.
Found in an Electronic Design from the 80's, this circuit monitors the charge of a 12 V battery....
Found in an EEE from 1970, this circuit supplies a voltage of 12 V DC x 10 mA current from the...
Using old germanium transistors like the CK722, this circuit has good gain. We found it in a...