This interesting circuit found in American documentation generates a busy signal, without you having to take the phone off the hook if you do not want to answer. The components used are common.
Interval pulses emitted by this circuit are picked up in a medium wave radio nearby. The circuit is...
This simple circuit serves to identify the terminals of a PNP transistor. For NPN transistors, just invert...
This oscillator generates quadrature signals, that is, with a 90-degree lag. The frequency is...