What makes it rather special is that it relies on only one type of device, every one of its transistors is a BC547. In design terms ... It doesn’t use the bidirectional amplifiers popularised ...

The circuit is a simple one, and a classic. The spring from a ballpoint pen is soldered to the base of a BC547 transistor, and when held close enough to a conductor carrying AC power, a current is ...

This sound alternator is designed to simulate the effects of a police siren, combining sound and light to create a dynamic ...