Found in a Popular Electronics from the 90s, this circuit can be adapted to use modern operational amplifiers. The output voltage is the square root of the input voltage.
Carbon microphones are no longer used in most projects. However, finding one in the scrap metal, it...
This circuit produces a strong tone of audio or ultrasound, depending on the values of components C1 and...
This alarm from an old 1978 publication uses PNP transistors and driver and output transformers that are...