This high-Q low-pass filter was found in the October 1990 issue of Radio Electronics magazine. The frequency depends on the capacitors used and is on the order of a few tens of hertz.
This repellent operates with frequencies from 30 to 45 kHz, serving for insects and rodents. The...
This circuit is from a publication from the 70s. The original text was kept. The medium...
We found this circuit in an old American publication. The transistors can be BC558 and diode 1N34....