This circuit, which can be used to indicate the movement of an object, was found in NASA documentation. The circuit uses a sensor made with liquid in a container as shown in the figure.
This polarity test or indicator indicates the polarity of a power line by LEDs. The circuit is...
This is the circuit of a digital clock published in the January 1975 issue of Radio Electronics magazine....
Found in an Elektor from the 90s, this circuit can be powered directly by the power grid. The...