This circuit takes advantage of the noise generated at the reverse biased junction of a germanium diode. Other types of diodes can be used. The signal is weak.
This small power supply is suitable for powering devices using 9V batteries. The circuit uses...
Found in a 90s Silicon Chip documentation, this circuit provides a current of 3 A and the voltages...
This sensor triggers an oscillator emitting sound when a magnet is approached by a reed switch....