This circuit was found in the August 1971 Radio Electronics magazine. The SCR admits equivalents and instead of the buzzer a sensitive relay can be used.
Other operational amplifiers of the same series can be used on this circuit found in Motorola's Linear...
This circuit uses a capacitor to store energy. The capacitor is charged by closing S1 by a moment. Them,...
Other amplifiers of the series like the MC3301, MC3401 and LM2900 can be used in this circuit. We found...