This circuit is from an old Popular Electronics, but it can be easily implemented nowadays, even adapted to act as a shield. The circuit has the frequency given by C1 and adjusted in R1.
This circuit allows you to find two diodes with equal characteristics. The circuit was found in a...
This small amplifier with the fraction-watt LM4862 was found in the November 1999 issue of...
The output of this circuit must be connected to the input of an audio amplifier. The microphone is a small...