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 circuit was found in a documentation from the 90's. Power is included, and the regulating...
We find this circuit in the 80s used integrated circuit manual itself. The integrated circuit is not...
This sweep generator or current-controlled oscillator was found in Popular Electronics from...