Found in an 80's Elektor, this circuit can use any equivalent optical coupler. The buzzer is of the Sonalert type with included oscillator.
This is the traditional configuration of Baxandall bass and treble control, using passive...
This circuit changes the dynamic range of an audio signal. The integrated circuit used in this...
Based on an LM317T, this circuit found in Popular Electronics works with signals of frequencies up to...