Found in American documentation from the 1980s, this circuit prolongs the ringing of a doorbell or chime powered by a 6 V continuous voltage. The transistor can be a BD136.
This circuit was obtained in a 1982 English magazine. This circuit can be used both as a simple...
This sensor triggers an oscillator emitting sound when a magnet is approached by a reed switch....
Suggested by Burr Brown in 1969 documentation, this circuit makes use of an integrated component...