This circuit is from a 1980s Signetics documentation but is valid for modern operating. Next to the diagram the formulas for the calculation of the components.
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...