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 is a simple converter or source configuration using an ordinary incandescent lamp as a...
This adjustable source was found in a 1979 documentation, but all components are still common...
The sensor of this circuit is a large surface diode. We believe that a small solar cell can also...