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How to Make an Infrared Proximity Detector

Infrared (IR) radiation is invisible to the human eye, yet in many ways it behaves just like light. Infrared light interacts with matter in the same way that visible light does: It reflects, transmits through, or gets absorbed. When it's absorbed, the absorbing material takes up the energy of the radiation. For example, when you put your porch light on at night, it transmits through the air. If people are walking towards your house, some of the light will reflect off them. Some of the light that reflects off them can get absorbed by your eye and the energy is translated into a signal that tells your brain something is approaching. Those same steps can be done with invisible infrared light and a photodetector.

Things You'll Need

IR LED package
IR photodetector
IR bandpass filter
Adjustable threshold detector circuit
Opaque divider
Mounting block

Instructions

- 1
  Attach the LED package to the mounting block.
- 2
  Place the IR photodetector on the mounting block so it faces the same direction as the LED. Face the detector to receive the reflected infrared radiation when the light from the LED reflects off an object.
- 3
  Place the IR bandpass filter in front of the photodetector. Match the wavelength of the filter to the wavelength of your LED so the filter will let the LED light through while eliminating other background light.
- 4
  Insert an opaque divider as a "wall" between your LED and the photodetector. This is to keep any infrared light from going directly from the LED to the photodetector.
- 5
  Connect the photodetector output to the detector circuit.
- 6
  Set the detector circuit threshold. Put your proximity sensor package close to the type of object you want to detect and adjust the threshold to trigger. If you adjust the sensitivity higher, you can detect the object when it's further away, but you will also be more susceptible to false alarms.

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