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 1968 General Electric documentation. It has an input impedance of 2 M ohms...
This protection circuit was obtained in a 1969 Electronic Design. The SCR can be the current...
This circuit was found on an old EDN and can be used as a shield. Optical couplers are from the...