One of their other habits is peeing in the box. If I get a chance, I'll have a go at that approach with some of our current residents to see if it's viable. It would need to be adaptive much like the way a PIR sensor works but over a much longer period (perhaps days) to overcome the capacitance change in the bedding as it changes with humidity. The capacitive approach sounds the most hopeful. This is one of their mechanisms to prevent 'others' such as rats from entering, so I don't think false triggers from rats will be an issue once it's occupied. Hedgehogs themselves are not very destructive but they make a LOT of mess and can (and do) 'deposit' six inches up a wall and in vast quantities. After a few months, mice had chewed the cables and that idea was completely abandoned. This worked for about a week before they became completely blocked by grime and assorted insects. I've tried a pair of IR sensors along the sides of the entrance tunnel. It's very difficult to dig one out because it is so tightly packed and pressed firmly against all sides. I also have my doubts about any form of pressure sense because when hibernating they cram as much 'stuff' into the box as possible. Trust me, it's not a viable method of detecting occupation during hibernation. Of course there may be long-term drift in the Touch value, but a "step change" (arrival/departure) over some seconds or minutes could be easily detected.Īll of our boxes contain IR cameras and microphones. The PICaxe can detect a change in the spacing of around 1mm (a difference of less than 1pF). My "capacitor" is two metal plates a few cms in area and a few mm apart (with air inbetween). I'm using a similar principle to detect a valve open/closing. The compressible dielectric might be plastic/rubber foam or even straw, with "sheet" conductors each side made of metal(ised) foil or a thin wire mesh/grid. I don't think that a single "Touch" pad would detect the addition of a small "body" above it, but I envisage a variable "parallel plate capacitor" in the form of a "mattress" covering the whole floor. However, a conventional "load cell" may not be needed. Also, a (micro-) switch based method is likely to need careful mechanical design and calibration of the threshold switching weight. IMHO an "analogue weighing system" would be a superior solution because adaptive software can discriminate the arrival/departure of one or more inhabitants from any "background" effects such as the addition of debris or bedding materials. A hedgehog is one of the few things we have that you guys don't! Two coils could be used to determine which direction the hog went in but that would be a rather expensive. I will be fitting coils to all our boxes soon but they will be located around the entrance tunnel to detect entry exit rather than occupation. This would work in a hibernation box if the coil was placed such that the hog was in or close to the centre of the antenna. So, far, the only reliable system is one using a large coil antenna and getting the hog to pass through it. I was hoping to get a system that would work when the hog passed over/under or past the antenna but this has proved to be unreliable. The challenge with RFID is getting any sort of range. In collaboration with a local rescue centre, I am currently developing an RFID system that will send a text via a GPRS module every time a tagged hog passes through the sensor. More recently, all the hogs that we receive from local vets and/or rescue centres have been fitted with RFID tags. The microphone can be used when they are awake but it can't detect the breathing of a hibernating hog. During the summer, the nesting material is light and the camera can be used.Īs soon as weather turns colder, the nesting material gets crammed in and the camera is of no use. We have several boxes with camera + microphone. When not hibernating, a simple temperature sensor works fine. Knowing the occupation of hibernation boxes has also been an issue for us. I was very intrigued to see this thread as my wife and I have been running a small home hedgehog rehabilitation centre for the last 20 years.
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