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.
Written in an article in Radio Electronics magazine in April 1987, this circuit triggers an alarm...
This is the receiver circuit for the previous transmitter. The circuit has a programming key to...
This is an example of a temperature sensor shield using the Texas Instruments TMP390 obtained from...