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 an Analog Devices publication from the 1990s. The circuit performs input...
This circuit is from a 1964 Electronic Design. The transistors are from that time. They can be...
Found in a 90s QST, this circuit uses an operational amplifier that is still common. It generates...