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 circuit is from a 1980s Motorola documentation. The circuit can be made with modern...
This well-known circuit triggers a relay when light striking the phototransistor is cut off. The...
This circuit generates a pulsed tone whose frequency depends on C2 and whose flashing depends on...