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 was found in an old American publication from the 70s. It flashes a warning lamp,...
This circuit can measure the power of loads up to 1 kW and its accuracy depends on the settings and...
This circuit, from a 1977 documentation, uses two 555 or one 556 (double 555), being able to...