We found this circuit in a 1976 publication. The transistors can be BC547 or 2N2222. Crystals up to a few tens of Megahertz can be tested. The LED can be of any type. The capacitors must all be ceramic.
This circuit for controlling a model of an elevator via wire was found in the December 1997 issue...
We found this circuit in the January 1979 issue of Radio Electronics magazine. Components are...
This variation of the previous circuit produces a pulsating sound when the sensor is activated. The...