The passive infrared sensors on camera traps differ between makes and models and some of them are heavily biased towards movement in certain directions - Reconyx for example is strongy biased to movement across the bottom half of the field of view, which means that an animal can walk stright towards or away from a Reconyx camera and only be detected when it is less than 2m away.
Some of the detection zone arrangement depends on the hardware of the fresnel lenses that are moulded into the window in front of the PIR sensor, and the number and arrangement of sensors on the PIR (usually only 2 or 4 as far as I know - the fresnel elements make the heat image jump from one to another as the target moves smoothly across the field of view). To trigger an image capture there must also be some logic processing of the rising and falling signals from the PIR zones - does anyone know, for any camera trap, whether this is firmware (i.e. in principal it could be modified) or is it likely to be locked into the hardware of the chips ?
14 March 2019 5:02pm
I can't speak for the more expensive camera traps but the cheap camera traps are generally based off a reference design that's provided by the main IC supplier. In many cases, this would be Sunplus, a Chinese chip fab. From my experience in manufacturing, I would say that the camera trap (trail camera?) supplier likely does not care about correcting across the differences between the Fresnel lens zones. What they do is copy the IC supplier reference design, possibly with some slight modifications, then have a test to see if the PIR sensor detects motion. If it does, then that particular test passes and if the other hardware tests pass, then the device ships.