Found in a 1980s American documentation, this circuit operates with 5 V signals requiring 55 cycles of 500 Hz for tone recognition. The circuit can be adapted to operate with other frequencies.
The sound produced by this circuit, from a 1978 publication, depends on the humidity between the...
In a September 1992 Radio Electronics article, we found this basic 555 circuit used to generate fixed...
This circuit is suggested by Motorola, using a 4N26 type coupler and an MC1733 type operational....