This 4-tube counter was found in Radio Electronics magazine from December 1959. The circuit uses a coil as a sensor to detect the passage of metallic parts or magnets.
This current-limited circuit was found in a Popular Electronics from the 90's. ...
In this interesting circuit, a common relay is used as a vibrator to obtain high voltage with a...
Nixie-type displays are no longer used except for assemblies of people who like old technology. The...