This high sensitivity circuit was found in the July 1992 Radio Electronics magazine. The circuit drives a buzzer, but a relay can be used to activate an external load.
This amplifier is from a 1990s Linear Technology component manual. The circuit requires...
This circuit is from Radio Electronics. The magazine no more exists, but the circuit can be...
Found in a 1965 Motorola documentation, this circuit uses a neon lamp as a trigger element. The SCR...