The working principle of this circuit is extremely simple and straight forward. When the infrared proximity sensor (E18-D80NK) senses an object in front, its internal NPN transistor pulls the output ...

The circuit can be constructed on a small piece of Perf board. Assemble R1 and IR LEDs on a separate board. Fix IR LEDs on one side of the entry and the Phototransistor on the opposite side. Carefully ...