Found in an 80's Elektor, this circuit can use any equivalent optical coupler. The buzzer is of the Sonalert type with included oscillator.
The supply can be between 4 and 10 V in this circuit and R4 is necessary when the supply is less...
This is an integrated recommended for portable amplifiers, recorders, and battery powered radios. It...
Found in American documentation, this circuit generates linear sawtooth signals using a constant...