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 is from a 1982 publication. It is a sequential effect of accelerated and intermittent LEDs....
This PLL with operational amplifiers was found in 1969 documentation. The configuration can be...
Here is a simple source without a transformer for currents up to 50 mA. The voltage depends on the...