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How to build test circuits for infrared IoT projects

Stephen Glasskeys | Aug. 28, 2015
Three easy to build infrared detector and emitter circuits.

Infrared test circuits
Credit: Stephen Glasskeys

If you are using infrared (IR) communications in an IoT, embedded, or mobile hardware project and are experience difficulty debugging IR communication, you can use the circuits below to eliminate a few doubts regarding the "physical layer."

In other words, using these circuits can help you ascertain that the device is indeed broadcasting IR signals and that infrared LED(s) and drive chips are working. 

Simple IR detection 

This easy-to-construct circuit causes a standard LED bulb to glow when infrared is detected by an infrared photo-diode or phototransistor. The third, remaining part, is a common 2N2222 (or equivalent) NPN transistor.    

Simple LED test circuit schematic
Stephen Glasskeys

Listen to light

However if you would rather hear an infrared beam instead of watching for one, this circuit should fill the bill. It uses a common 555 timer to pump a tone through a standard 8 ohm speaker, but only when the IR source is strong enough to be detected by a photo diode.

Because this circuit can generate a very loud tone, a 5K potentiometer can be used to turn down the volume. Press the (normally open) test button to validate that the tone circuit works properly, and when you adjust maximum volume. 

Hear a tone when infrared is detected
Stephen Glasskeys

Now you see it, now you don't

If you want to test drive your newly constructed detector but don't have an IR source within reach, the next circuit should help you out. It too implements a 555 timer IC, but instead of driving a speaker, it pulses an infrared LED emitter five to seven times a second (5-7 Hz). An additional non-infrared LED is also wired in parallel, used to indicate the instant each IR flash takes place.

Generate infrared pulses
IR pulse generator. Credit: Stephen Glasskeys

Demos

The following video (link below) demonstrates the IR pulse generator and both detector circuits.

Direct link: https://youtu.be/_wuOgKX7jIM

Finally, if you are curious about the Apple Remote's IR signals, watch this:

Direct link: https://youtu.be/hfuFE9Nx6nM (direct link).

 

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