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 takes advantage of the inductance of the coil of a high-impedance phone to form the...
This circuit controls a fan in the car, according to the temperature, activating it automatically when the...
In relation to the previous circuit (CB18493E) this spy has an extra transistor, which can be a...