This circuit was obtained from an 80's EDN. The components used are still common. The circuit can be used as a shield and the frequency is approximately 775 Hz.
Using two 567 PLLs, this circuit recognizes two audio tones in sequence providing a signal for a...
We found this transmitter in a documentation on espionage from the 90s. The circuit is...
We find this circuit in a Radio Electronics of July 1984. It consists of the traditional version of 1 A...