When the voltage in the circuit exceeds the value set in the trimpot, the LED goes off and, if a low current buzzer is used, it rings. The circuit is from American documentation from 1999.
The base of this circuit is one of the four Norton amplifiers existing in an LM3900 integrated circuit....
This simple CMOS metronome circuit can be mounted in a small box, providing both sound and light...
This circuit of an old American publication uses RF transistors to obtain unit voltage gain, but...