Argon Constantly Triggering PIR on Regular Cycle

Hardware
1

I’ve been working on a rather maddening project lately, and after extensive testing and research, I’m about ready to throw in the towel and move to a different platform.

I have a common PIR sensor (picture below). When connected to an Arduino UNO it works perfectly. Triggers when it should, and stays quiet the rest of the time.

As soon as I move this sensor into an analogous Argon project - using the exact same connection leads - it goes nuts. The PIR is getting triggered by something on the Argon on a regular interval. It’s a very regular pulse. I’ve tried filter caps (10uF, 1uF, 0.1uF), ferrite chokes, and nothing stops this when the project is running on the Argon. If I move the sensor back to the Uno - with the same connection leads - it’s fine. So I know it’s not anything with the sensor itself.

Code? In addition to the stock example code provided by numerous online sources, I have combed the web for various sketches (including this site) to build in ways to adjust the sensitivity. Up to 6 sketches, with different approaches, all result in the same thing. The only thing that seems to vary is the frequency of the trigger. Sketch A might be 80 seconds, while sketch C is every 60. One outlier sketch was every 5 seconds.

Environmental factors? Turned off things like LED lights and such, but again - if the sensor works on the Uno in this environment, why would that matter? In any case, I’ve noticed no other devices causing this interference. I even took the project down to the basement to see if a complete change of venue would provide any insight. Same issues. Everything points to something on the Argon itself.

Power? I’ve tried LiPo, USB power from my laptop, and a USB wall adapter. No difference.

I know PIRs are notoriously finicky, but since I have a working project on Uno, I don’t see why the Argon is having so much trouble on this. Also tried a second Argon - same thing.

PIR_25xHk

2

This is just a guess:

How are you powering the sensor? The Arduino Uno is a 5V device, and the Argon is 3.3V.

Many PIR sensors required a minimum of 5V, so you can’t power it by 3V3, only VUSB, and that only works when powering by USB, not battery. However do not do this until you verify the operation of the sensor.

The Argon is a 3.3V MCU that is not 5V tolerant, so if the High/Low output is 5V when powered at 5V, it will damage the Argon.

However some PIR sensors have a 3.3V push-pull output even when powered at 5V, so those are fine. There are some cases where the PIR sensor is an open-collector output, which is OK, but you also need an external pull-up to 3V3. You can tell this is the case because the output is always 0V even when triggered unless you add a pull-up resistor.

Also VUSB isn’t really 5V, it’s more like 4.8V, so that can be an issue sometimes as well. It’s because there’s Schottky diode to prevent power from flowing into the USB connector when powering externally by VUSB.

3

Yes, the PIR needs 5V. Power to the PIR here is from the VUSB on the Argon. So if the VUSB isn’t really 5V as you indicate, then that could be the issue.

I’ve ordered some other PIRs and will test with those.

4

I have used this sensor for the Argon device with good results:
https://www.sparkfun.com/products/13968

5

Thanks. I suppose you get what you pay for, but that is out of scope for now at $17.50 a pop. I’ll report back on the others I’ve ordered.

6

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