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.
This circuit was taken from the 1974 Ferranti transistor manual. Transistors are common types at...
This circuit monitors the current of a series of 40 V lithium battery packs connected in series....
This 1970 Philips circuit uses a mechanical counter. The circuit is triggered by a reed switch...