Taking the NXT hiking... as an altimeter

I recently returned from a wonderful week-long vacation in the Rocky Mountains here in the US, and of course took along the NXT. I mentioned before that I was trying to get the NXT to function as a pedometer to record footsteps for a project I was working on. Well, I didn't get the pedometer working, but I certainly had fun on the project...

The HALE mission is rapidly approaching, and one of the things I wanted to do on my payload was fly a good pressure sensor. A really good one, with possible vertical resolution in the range of a meter or better. After some discussion with the folks over at Hitechnic, they were able to put together a prototype for me to fly with very high resolution. But how to test it? First, I made a small vacuum chamber from a Tupperware bowl, aquarium supplies, and a large-bore syringe, testing it out under hot sun & in my freezer (my wife did look at me a little funny...). It worked rather well, but I wanted more. Since ultimately the HALE pressure data would be useful to determine altitude, I decided to test the pressure sensor by taking it hiking. First was Picacho Peak in the Dale Ball trails just outside of Santa Fe, NM. It worked wonderfully here, logging the pressure & temperature for over 2.5 hours, and allowing me to reconstruct a very accurate profile of my hike. But for HALE, I'd need more - more calibration points, & more data storage. So with the help of some friends on NXTasy, I developed an NXT-G data compression scheme & took the NXT to Rocky Mountain National Park. Ultimately the NXT could be toggled between two logging speeds, and a touch sensor allowed the user to input "notes", a brief numeric code that would be time-stamped to a record to notate important places during the hike. This way, I'd be able to calibrate the sensor at known elevations (ones much higher than those available to me in Indiana) under "field conditions"... and have a lot of fun generating profiles of my hikes to boot. Think of it as the LEGO geek's answer to commercial altimeters (I had one of those along as well, for calibration).

This worked out better than I could have hoped. Not only was I able to capture a good elevation profile (as good as the commercial units, actually), but I could do it at a far higher time resolution (on the order of a few seconds) over the entire day, and under my control, adding notes when I wanted (such as at important trail junctions, on top of peaks, or to mark rest breaks, etc.). The result is a gallery of trail profiles (altitude vs. time - your speed may differ) for a number popular trails in the Rocky Mountains, like Twin Sisters peak, Flattop, and up to 12,700' on Hallett Peak (as well as some off-trail bushwhacking adventures my wife had some strong words with me about). You could see when I rested, or what my ascent rate was (at times around 1,400' per hour, not bad for me, a "lowlander", at that elevation). I could record the profiles of the car drives, and even the airline flights as well. The unit also recorded the sensor temperature, so I had a rough record of what the temperature was at each step in my hike as well. Ultimately the sensor was precise enough that I could watch it change even as I went up the steps in the hotel (or if I threw the unit high in the air), & on the trail it showed every hill and minor rock outcrop I climbed.

Now admittedly I did this with a very special, high-resolution sensor, and it took some calibration on my part as well. But it's a nifty example of taking the NXT out of the world of toys and into environments & situations that LEGO almost certainly never intended it (& I don't recommend this for survival situations - the right gear for the right job!). In a future post, I'll review some of the existing commercial pressure sensors out there to determine how well they work (I have two that I purchased from Vernier and one from Mindsensors). Even the battery life surprised me - I used Lithium E2's for their light weight and long lifetimes, and was not disappointed, with the unit logging for more than 54 hours worth of run-time before the batteries finally died on the trip home... and even then, the NXT preserved the data.

Not bad for a toy :).

Brickshelf Gallery of RMNP graphs

Brian "now, if Long's Peak would just clear of snow..." Davis


Damien Kee said…
Fantastic work Brian!
Anonymous said…
It's posts like this that keep nxtstep in my web browser Favorite list. This blog is the best nxt resource out there for ideas and inspiration!!! Keep it up!!!

BlueToothKiwi said…
Yeap - I agree with Keith above...

I been looking forward to reading about this since you got back from your holidays - and as ever, you never let anyone down! Great work and a good write up - Well done.
Brian Davis said…
I'm happy you all enjoyed it so much. The results were much better than I hoped... and yet the coding that went on "behind the scenes" was an amazing adventure that is difficult to blog about properly. The thread on NXTasy gives you a flavor of the process, and I hope you enjoy the resulting graphs.
NickNackGus said…
I am working on rebuilding my school in LeoCAD, and plan to use my two NXTs, RCX, and/or spybot to build a rough map of the elevations in my school. Could you send me the formulas and parts used in your altimeter? Will anyone notice the NXT tracking my every move and mapping the school? Can you please ignore the second question seeing how I'm going to program my robot and will know what it records?

My email is NickNackGus@gmail.com

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