This simple tester was found in a Popular Electronics from the 90s. The circuit is powered by two 9 V batteries since it requires a symmetrical source.
This circuit is characterized by the configuration that accelerates the switching, being ideal for the...
We found this version of the automotive tachometer in a 1980s publication. Variations from other...
Found on 80's Popular Electronics this circuit operates at 455 kHz. The explorer coil is formed by...