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IR Beacon pairs not functioning as expected

Hello Pololu engineers.
I recently purchased 2 pairs of IR Beacons (#702), wired them and started testing… Unfortunately, when paired, the beacons keep lighting the red LED’s randomly. I tried using the “paired” units or units from different pairs with the same result. I also tried all combinations of 2 beacons, either in a small room (maybe stray reflections, or in a large room (>10ft distance to the next wall) while the units are a couple of feet apart.
For power supply I use LiFePO4 2s (6.8V). Would you have a simple PIC sample code which just creates 56kHz modulated square wave at, say, 1kHz? Would the individual beacons #701 perform differently?

Thank you for your help.

Here’s a short movie depicting the behavior…
Thank you.

Hi, Radu.

I am sorry you are having trouble with your beacons. Thank you for posting the video. I do not think the video caught the start up sequence for your first beacon, but on the second beacon I noticed one of the red LEDs flashing 4 times after start up, indicating that one IR receiver is not connected properly. Could you post pictures that show the solder joints on your beacons? Have you tried testing them in other lighting or with the lights off? Please also make sure you are not testing near a window since sunlight can interfere.

The beacons are sold in pairs for convenience, but both units run the same program, which is the same as the program on the units that are sold individually. We do not make the PIC source code for the beacons available, and we do not have any simplified versions you could use to test.


Thank you Claire for your response. To answer your question, all IR sensors are mounted as intended and all 4 x 4 work as intended, as it is possible to get them to run by fiddling with the relative position of the beacons, covering the back sides to prevent stray reflections, etc.

  1. once in a while, upon powering up the first sensor, it turns on a red LED when none is expected.
  2. once in a while, upon powering up the second sensor, it will flash all 4 LED’s and then work as expected. I attribute this behavior to my crude test environment where the V+ connection (alligator clip to stranded wire) may be bouncing. I noticed this behavior with several of my 4 beacons.

I will continue my research to understand the optimal operational conditions of these beacons and post my results.

As you mentioned alligator clips are not the best for reliable connections, so changing to something more secure might save you a lot of troubleshooting headaches. Besides that though, it is hard to tell what is going on from the information you have posted so far. If you need more help troubleshooting, feel free to post pictures of the beacons and soldering and I would be happy to look for any potential problems.


Thank you Claire.
As advised, I checked the connections - they are all OK. I suspect stray multipath reflections - my environment is all white walls and light colored, polished ceramic floors. I will scope out the wakeup/advertise/receive modulated pulse train to better understand the robustness of the algorithm. Moreover, I will play with IR-absorbent material to block back and side reflections from the receivers and limit the elevation angle of the emitters. Ultimately, I may rewrite the PIC algorithm to account for difficult environment conditions.
I will keep you updated.