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Firewalker - Velostat range
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Please be positive and constructive with your questions and comments.

Firewalker - Velostat range

by Rek on Sat Feb 13, 2021 1:11 pm

I made the original firewalker shoes with Flora and velostat step sensors. I'm loving them, but I have an issue with the velostat. The range I am getting from it is VERY narrow. The "resting" reading is around 65 and the "pressured / activated" reading is around 40-30. This narrow range comes in as a very bouncy reading and every activation seems to immediately jump to the 3 step limit. While the bright LEDs look cool, I was really hoping for the more shimmery effect.

Is there any way to help the velostat create a greater range? I'm using 26 AWG stranded sillicone wire from adafruit instead of conductive thread for weatherproofing. My shoes are size 12. (I'll try to take some pictures for size reference.) I'm curious if adjusting either the surface area of the velostat, or the amount of exposed wire in contact with the velostat, can make the difference I'm looking for?

I'm completely willing to test different layouts on my own, but thought I would ask here first in case anyone has already put in the effort.
Rek
 
Posts: 2
Joined: Wed Jun 26, 2013 3:39 pm

Re: Firewalker - Velostat range

by Rek on Sun Feb 28, 2021 3:21 pm

Measuring velostat surface areas, wire lengths, cross over, etc and so forth sounded like such a grand time that I...

Completely went a different direction. I wrote some changes in to the Firewalker code that tracks the range between the highest upper reading and the lowest lower reading, and uses the median between those to make a snap decision about what range the current reading likely falls into. After that, I track 100 (this is configurable, just don't do 1000 because there's not enough memory. Oops.) of the previous upper and lower readings and look for ones that fall into a specific distribution. I use the boundaries of my distribution (fuzziness 10%) as my trigger and hysteresis values. Then, finally, if the velostat shifts its resistance over time, and I start getting a string of values outside my expected ranges, there's a configurable weight that says, "after enough bad values, start with a fresh set of readings".

So far it's been working great with the two shoes that I have to test it on. I had been dreading the need for constant calibration of the velostats for the shoes I wanted to build for my son, but now that I have a more flexible setup I plan to start on his soon!

Also, also .. since this was my first attempt, some glorious mistakes were made. The biggest was that I accidentally REVERSED the direction of the Neopixel strip on ONE of my shoes. I had to re-write the Firewalker code to handle that mistake. Fortunately I've got it straightened out now.

All in all these shoes are AMAZING and I love this project. Thanks so much, to all the wonderful folks over there at Adafruit!!

Next up on my list is to implement a push button for FLORA to swap between some pre-defined color ranges.
Rek
 
Posts: 2
Joined: Wed Jun 26, 2013 3:39 pm

Please be positive and constructive with your questions and comments.