Sunday, 26 April 2015

I'm sure they're smaller in the movies


Having sussed my software stability problems with the LLAP serial library I polished off the GPS tracking tag I've been making and took it out for a range/accuracy test in the sort of environment it'll get used in, ie. a large hilly wood.

This weekend was our first Lasertag event of the year and the site is a good example of the sort of thing you see in LARP. I wasn't expecting a massive range but in the end was a bit disappointed with only about 50m.

For this I did a slightly unscientific test using a USB stick radio and wandering off with a laptop until I stopped seeing packets from the tag. The USB stick only has an integral chip antenna so I'd expect a bit more with a wire fitted, but this is nothing like the 150m I'd hoped for.

Still, my plan was for this stuff to work in a mesh as even 150m isn't very far in a large wood, so making some high power transmitters with decent aerials to act as relays was kind of always on the cards.

This particular box is just a proof of concept so I can test range/meshing but it'll serve as an anonymous tag that could be taped to a prop that can be 'tracked' or left in a location for people to find their way to.

The good thing is that under the trees the GPS module gets accuracy 100% of spec or occasionally better, so that's down to a 2m area. Which is great, 5m or so would be good enough.

I already have a couple of high power radios and sticking them in boxes to act as relays should be fairly easy. The sticky bit will be the software, so I mustn't underestimate how long that will take. It always takes me 2-3 times longer than I leave time for and I end up pulling some late nights before I need it.

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