This filter was found in a Texas Instruments manual based on an operational amplifier 741. Other operational can be used and, with the indicated components, the rejection frequency is 2 kHz.
Vox or sonic switch is a relay activated by the voice or any sound picked up by the microphone. This...
Found in a Popular Electronics from the 90s, this circuit can be adapted to use LEDs. The power...
This basic circuit is from 1984 documentation. This circuit can be used as an efficient burglar alarm...