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 is from 1997 documentation. It uses CMOS circuits to produce the effects, being...
This circuit is from a 1979 documentation. The critical component is the CA3130 operational...
This circuit was obtained in a Motorola documentation from 1968. The circuit uses a power...