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.
The presented circuit has a stabilization with the LM313. The components used are uncommon, such...
This circuit makes use of a transconductance operational amplifier. It generates signals with TTL...
In the figure we have two typical configurations of voltage regulators with protection against short...