This circuit produces the sound of a motorcycle or an outboard motor. The frequency is adjusted in the pot. For supplies above 9 V the BD136 must be equipped with a small heat sink.
We can use the circuit shown below, obtained from a 1992 documentation. To turn a low impedance phone...
High-brightness LEDs of various colors and even white can be obtained easily in specialized...
This circuit is from an American publication about old neon lamps. The circuit is leak proof and...