Found in the October 1979 Radio Electronics magazine, the purpose of this circuit is to monitor the coolant level in a car's radiator. The circuit is based on the LM1830.
This conventional astable multivibrator circuit with operational amplifier can be found elsewhere on...
Using red LEDs with ignition voltages of the order of 1.5 V we can make a multiple voltage...
This old circuit (1968) uses a germanium transistor to drive a relazy from a switch. The circuit...