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.
We found this circuit in a National Semiconductor publication from the 1990s. The circuit has an...
This circuit uses a 100 kHz crystal, but nearby frequencies can be obtained with appropriate...
The transmitter can be that of CB9574E. This receiver uses a PLL to directly trigger a sensitive relay....