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, which uses a planar silicon sensor, is from a 1964 Electronic Design. The component...
This circuit is from 80's documentation. Operational equivalents can be used. The power source is 5 V...
Delayed Pulse Generator This can be considered an "advanced" application where two 555 integrated...