This circuit memorizes through an LED indicator if your phone was used during your absence. The circuit was found in a 90's EDN. Transistors are commonly used.
Other series amplifiers such as the MC3301, MC3401 and LM2900 can be used on this circuit. We found...
This circuit is from a Radio Electronics magazine from February 1992. The circuit has the effect...
This simple circuit tests both monophonic and other two-wire audio cables. The circuit is powered...