This circuit from an old documentation includes the power supply for the 117 V power grid. It can be adapted to other networks by changing the 10k resistors.
When the sensor, an ordinary photo-transistor, receives light, the relay closes its contacts. The...
This circuit consists of a bass filter that can be used as a subwoofer in a sound system. The...
This circuit has a traditional configuration often found on this site. The transistor must be...