This filter was found in an old publication from 1977. The circuit must use a simple two-voltage source and the components can be changed for operation at other frequencies.
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...