Using red LEDs with ignition voltages of the order of 1.5 V we can make a multiple voltage reference. Current is low.
This circuit produces a clef sound when a pulse is applied to its input. The damping effect is...
This circuit can serve as the basis for a simple phone. The LM10 is not common today, but the...
This is a possible circuit for the receiver of the previous circuit. Other circuits can be found...