How to build test circuits for infrared IoT projects

Three easy to build infrared detector and emitter circuits

If you are using infrared (IR) hardware in an IoT, embedded, or mobile hardware project and are currently experiencing difficulties debugging IR communications, using one of the circuits shown below should help you determine if "physical layer" issues are responsible for problems or bugs.

In other words, using one of these circuits could help you determine if the device is indeed broadcasting IR signals and that its infrared LED(s) and drive chips are working as intended. 

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 a bulb, 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 adjusting 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 Stephen Glasskeys

IR pulse generator


The following video demonstrates the IR pulse generator and both detector circuits 

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

This story, "How to build test circuits for infrared IoT projects" was originally published by ITworld.

Copyright © 2015 IDG Communications, Inc.

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