This sequential circuit of LEDs was found in a Popular Electronics from the 90s. The circuit can be programmed and an adaptation consists of using optical couplers to drive power loads.
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...