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 shield circuit is suggested by Texas Instruments and can employ almost any optical coupler...
In the figure we have a monostable that is activated with switch S1 and pressed for an instant. The...
This circuit for alternating current was found in a 1965 General Electric documentation. The...