Fabric Bend Sensor

Step 5 Closing the sensor

Before closing the sensor you will want to cut out a piece of Velostat that is just a little bit smaller than your pieces of neoprene. This piece of Velostat will go in between your two conductive stitches. And this is what creates the pressure sensitive change in resistance. The Velostat lets more electricity through, the harder you press the two conductive layers together, with the Velostat in between. I'm not really sure exactly why this is, but I imagine it's because there are carbon particle in the Velostat that conduct electricity and the more pressure on them the closer they come together and the better they conduct or something similar (???).

So, place the piece of Velostat in between and sew the sensor together as shown in the pictures. Don't sew too tightly, otherwise you'll have an initial pressure which will make your sensor less sensitive.

Comments

[azdelslade]

hi, first off, thanks for the brilliant instructable! i made one of these with all the components you listed here, neoprent and actual velostat. i can get readings off of my multimeter fine and change an led with a battery fine, but when i hook it up to my lilypad, I only see changes between 1023 and 998, which is not much. I tried loosening up the stitches and using digital 5 as a power source instead of +, but it doesn't seem to help. Any suggestions? When I put my multimeter on 200k i get readings between 20 and 0.5. I tried adding 10k, 1M and 10M resistors, but that still didn't improve the sensitivity. I also tried adding another piece of velostat.

[azdelslade]

I was able to get a decent reading by making a voltage divider circuit, after looking at this lilypad flex sensor example: http://mtifall09.files.wordpress.com/2009/12/rhinoglove.pdf

[Plusea]

yes, you need to use a pull-up resistor (voltage divider) around 10-20 K Ohm which you can also set in software for the lilypad arduino by writing "digitalWrite(14, HIGH);" in setup for analog 0.

[leisure1231]

which kind of sensors do you choice?

[Geemge0]

Is the stretch fabric doubled over in this? Or is it simply one layered slice of it? Great guide btw.

[Plusea]

the stretch fabric is neoprene. it is 1,5mm thick with jersey fused to each side (one side green, one side grey). so there is only one layer of neoprene for each side. does this answer your question?

[chuckw]

Why does it look like the Velostat isn't sandwiched between the top and bottom layer in a few of those pictures? ..Chuck..

[Plusea]

So that i could show how the stitches "meet". That if you stitch two identical layers the stitches will crisscross when facing each other. That is why i took the Velostat out so that people could see.