This circuit was found in a Popular Electronics from the 90's. Its purpose is to detect the ionization of the air. The meter can be replaced by the current scale of an ordinary multimeter.
This circuit is from a 1982 publication. It is a sequential effect of accelerated LEDs. The...
This circuit was obtained from an Electronic Design from 1964. The components used are from the...
This circuit reinforces the treble, working as a booster for instruments or home theater. The...