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.
An excellent low frequency sine signal is produced by this oscillator. The frequency is determined by the...
Using the 4046 PLL integrated circuit, this circuit generates signals from 60 Hz to 1.4 kHz via...
This circuit of the 70's uses transistors of the time. The circuit can amplify signals from 10 Hz...