This circuit for audio signals was found in the March 1990 Radio Electronics magazine. The circuit uses a unusual optocoupler that can be replaced with an equivalent one.
This powerful amplifier was part of commercial sound circuits from the 90s. The integrated circuit...
This circuit generates a control tone that serves to adjust amplifiers, check audio cables. The...
This circuit locks when the sensors are opened. The relay can be 6 or 12 V depending on the power...