The Numbers

A project log for DWM1000 Cat Tracker

Using the DWM1000s amazing ability to pinpoint tags to within 10cm we will track the cats positions in the house with amazing precision.

dryerziniaDrYerzinia 06/28/2016 at 04:380 Comments

After a lot of testing I've found it to be exceptionally accurate in free space but there are issues when signals have to travel through walls. With the anchors upstairs and the power maxed out I can just barley get full coverage of the house. (3 stories about 40ftx40fx)

The very first measurements I did showed a standard deviation of exactly 10cm. Right on the spec, however the absolute measurements where a bit off and I need to calibrate it on all the devices still.

So the results don;t really fit a bell curve but the standard deviation was 10cm and the worst overall difference was about 38cm. This is with the transmitter and receiver both just sitting in the same spots for about 30 samples. It was also a short range test in the basement. To really get a good idea of how well these work we will have to look at tests with all 3 anchors in place upstairs and the tag in various places.

In this image you can see the received points in various places in the house and the associated standard deviations. The lone red dots show the anchor positions. Some of the results are excellent. And some are oddly erratic. The best I can guess the erratic once must be because of duct work or other metallics in the way of the signal. There was never a sever deviation on all 3 nodes.

The Guest Bedroom Window in particular had quite the variation in its measurements to the BA5E node which is the furthest left anchor. The other 2 anchors had standard deviations less than 2 cm supposed to its 21 cm error. This results in a large amount of uncertainty along a line in 3D space.

The Livingroom Corner result was another oddity. Perhaps some one moved into the RF field skewing the results for a while. There appeared to be 2 relatively well matched groupings spaced slightly appart. I suppose it could also be a result of a sudden shift in the crystal frequency of the tag or the ancors, but that seems unlikely cause it affected 2 of the anchors rather than all of them or just one.

Overall the position reported was pretty much always within 30cm when it was working well, but when there were what I assume where multipath issues it significantly increased to up to 2 meters of error. It will be enough to know the cats are safe in the house and to figure out where they are pretty quickly.