A while after I started to use a Raspberry Pi Zero W for this project I noticed some odd behaviour. When it came to reviewing the images on the USB drive, I noticed there were far more images/videos captured then I had expected. Most of the time, there was nothing to see in the videos (i.e. the PIR was being triggered by accident).
My initial thoughts were that the PIR sensitivity potentiometer was set to high and that even the slightest movement was triggering the camera to begin recording. However, after altering the sensitivity, the problem persisted.
Luckily, one of the readers of this blog, Barry, has tracked down the issue and worked out a fix!
It turns out the RPi Zero W sends out a WiFi polling signal every 2 minutes to check for any networks it can connect to. Doing so, it activates the PIR and triggers the camera to being recording. Bummer.
Of course, one option is to turn off the WiFi on the Raspberry Pi which should solve the issue but then you run into the trouble of having to turn it on via a cable or using another Raspberry Pi with an ethernet port. This isn't the worse thing ever but it the whole point of having built in WiFi to the RPi is so that we can easily modify the trail cam program without complication. If you want to go down this route, you can turn off the WiFi completely by adding
dtoverlay=pi3-disable-wifi to the
config.txt on the boot partition of your Raspberry Pi. Only do this if you know you can switch it back on again later!
Barry's solution is more practical and involves shielding the PIR with metal sheeting - he used thin aluminium from a floppy disk casing (you might be able to use tin foil) and grounded it to a ground pin on the Raspberry Pi's GPIO. He then used a ferrite ring on the PIR wires to further shield them from the signal.
Here, Barry has covered some thin metal with masking tape to avoid shorting the PIR's PCB and grounded the box to the RPi.
The ferrite ring (under the green, red and orange wires) around the PIR wires.
I have yet to make these modifications to my own trail cam and test the results but Barry reports that doing this should significantly cut down false triggers which, in turn, saves a lot of battery power and keeps your trail cam running for longer!
A huge thank you to Barry for getting in touch about this issue and then going on to research it and come up with a solution. I've not got nearly the level understanding he does so without his knowledge, I'd be flummoxed.
If you've experienced this issue (and solved it), leave a comment below and let me know.