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.
This filter, from an audio publication from 1977, passes the frequency range corresponding to the...
In the figure we have three voltage doubler configurations that can be used in high and low...
This circuit was found in Motorola documentation from 1966. The lamps are according to power and...