This 1974 circuit uses two 555 integrated circuits in a very traditional configuration. The circuit can be powered by voltages from 9 to 12 V and for greater volume an amplifier stage can be added.
We found this circuit in a 1956 documentation from Sylvania. The circuit is for bench testing and...
This circuit was found in the Radio Electronics magazine of July 19666. The search coils are the...
This circuit allows only signals with frequencies below the calculated value to pass. The formulas for...