This circuit is from an 80's technical newsletter. The circuit can use any general purpose transistor and its power supply can be changed with a resistive divider to use a single 9V battery.
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...