Infrared Proximity Sensor

As promised, you begin with a project that is straightforward and not too difficult. An infrared (IR) proximity detector is a combination of an infrared emitter and an infrared detector. The very simplest implementations of this circuit suffer from some pretty severe performance drawbacks, but they can still be used in certain controlled situations to accomplish noncontact proximity detection.

The emitter is usually an IR LED. It looks just like a visible-spectrum LED except you can’t see it shining. These LEDs are usually packaged in clear resin, although you sometimes find them in various shades of gray, blue, or pink. An IR LED’s forward voltage is much lower than a visible LED’s, usually in the 1.2V–1.5V range. Ideally, ...

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