This circuit is from Philips' 60s documentation. The circuit can be applied to modern operational amplifiers. The power supply must be symmetrical.
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...