Fabric Bend Sensor

Step 1 Materials and Tools

MATERIALS:
The materials used for the sensor are basically cheap and off-the-shelf. There are other places that sell conductive fabrics and Velostat, but LessEMF is a convenient option for both, especially for shipping within North America.

Velostat is the brand name for the plastic bags in which sensitive electronic components are packaged in. Also called anti-static, ex-static, carbon based plastic. (So you can also cut up one of these black plastic bags if you have one at hand. But caution! Not all of them work!)

To make the sensor fully fabric one can use EeonTex conductive textile (www.eeonyx.com) instead of the plastic Velostat. Eeonyx normally only manufacture and sells its coated fabrics in minimum amounts of 100yds, but 7x10 inch (17.8x25.4 cm) samples are available free of charge and larger samples of 1 to 5 yards for a minimum fee per yard.

The exact neoprene i used for the bend sensor is:
quality: HS
thickness: 1,5 mm
both sides: nylon- / polyesterjersey (standard)
one side: grey, other side: neon green
but you can defiantly try and experiment with different qualities and thicknesses!
also with different materials. i can imagine that foam rubber and similar will work.
one good thing about the neoprene is that it has jersey fused to either side which gives it a nice feel against the skin but also makes sewing easier, as stitches otherwise rip through the plain neoprene.

- Conductive thread from www.sparkfun.com
also see http://cnmat.berkeley.edu/resource/conductive_thread
- Neoprene from www.sedochemicals.com
- Stretch conductive fabric from www.lessemf.com
also see http://cnmat.berkeley.edu/resource/stretch_conductive_fabric
- Fusible interfacing from local fabric store
- Regular sewing thread from local fabric store
- Velostat by 3M from www.lessemf.com
also see http://cnmat.berkeley.edu/resource/velostat_resistive_plastic
- Machine poppers/snaps from local fabric store

TOOLS:
- Pen and paper
- Ruler
- Fabric and paper scissors
- Iron
- Sewing needle
- Popper/snap machine (handheld or hammer and simple version)
- Possibly pliers for undoing poppers

For connecting to your computer:
I'm not going to go into detail here, because this Instructable is really more about the sensor itself and less about this connection. But if you have question just send me message.
- Arduino physical computing platform from www.sparkfun.com
- Arduino software free from www.arduino.cc
- Processing programming environment free from www.processing.org
- Crocodile clips from www.radioshack.com
- A pullup or pulldown to the ground of your Arduino, with a 10-20 K Ohm resistor
- Some wire and solder and stuff

Comments

[windrago]

I am following your instructable right now - I have only one question where do I get the software that you use for the measurement? (the graph that you show in the video)  - I have been on arduino web site but I didn't see anything. I am new and exicited at this.

[Plusea]

The graph is written in processing (www.processing.org). you can download processing for free and you can download the graph code from the Instructables.

[tewfik]

WOW Really nice thing you've done here. I love the concept, could be used as you depicted as a glove-control-interface according to your video, it seems that you need some noise-filtering on pc-side (or arduino-side), just a thought you said that it is possible to measure the angle from this sensor, is it linear (ideally) or something non-linear and by the way, is the conductive fabric available or is it a special material you have to order on the internet ? very nice instructable thanks for sharing

[Plusea]

Hi. thanks for the comment.
some more noise filtering would be nice. i normally just threshold the data (min, max) and then i at least get rid of the annoying flickering at both ends. i'm not a big programmer, but i'm sure more can be done.

you're right the decrease in resistance is not linear, it is much more sensitive to slight pressure and then becomes less sensitive the harder you press, but it still gets information in the high pressure (human finger pressure) range. still it is stable so you can/could approximate angle from it.
if you use Eeonyx's carbon fabric instead of the Velostat then you get more linear results, but this fabric is only available in large quantities.

the stretch conductive fabric that i use is really easy to order from LessEMF over the internet. they are based in NY but ship all over the world (i think). their stretch conductive fabric is not the cheapest and just went up in price to 60$/linear foot (= 30 x 110 cm). but you can also use a less expensive, non stretch, conductive fabric or probably also use conductive thread to make a good connection to the popper... or even don't use a popper at all but sew directly to something else (a perfboard for example). but stretch conductive fabric is cool.

greetings!
hannah

[endolith]

What's the circuit connecting the sensor to the Arduino? The sensor is just one half of a resistor divider to the ADC? You could do digital filtering in software, but it might be easier to do it with just an electronic filter.

[Plusea]

the circuit is just a series of pull-downs. if you have any tips on doing some electronics filtering, i'd be very interested to hear.
thanks

[endolith]

By "series" you mean "one resistor divider for each sensor"? Just putting a capacitor across the sensor terminals will act as a low-pass filter and get rid of some of the fluctuations.

[Plusea]

yes. one 20K resistor to the ground for each sensor. i'll try out the capacitor next week. thanks!

[endolith]

So try a 1 microfarad capacitor across the 20K resistor. That will start filtering at 8 Hz (8 vibrations per second, still high for hand movements). If that doesn't do anything noticeable, try 10 microfarad, etc. If you go too high with the value it will respond very slowly, though, so you have to find a good value for the response you want.

[tewfik]

yes, a low pass filter will do fine, also you will decrease the cutoff frequency of your system and thus you won't sens rapid movements / variations (well, this is the role of a low pass anyway)

maybe a bit of processing on the microcontroller would be nice too
i find that moving average filters give good results, and maintain a good level of accuracy

if you want to have some "high"-tech filtering, try kalman filters, this is like magic ! kalman filters can handle high frequencies while rejecting noise effects without disturbing the system dynamic, also, a bit pain to implement , especially on 8bit systems

Moving Average - Wikipedia

Kalman Filter - Wikipedia

[gerritzalm]

Hi, Currently i'm building the sensor for a graduation project, but I have big problems finding the Velostat in the Netherlands/Europe. Any advice to replace it/use different material(s) or a fine webshop? Thank you very much

[Plusea]

you should easily be able to get it from your local electronics store. ask for the blank anti-static bags used to package/store sensitive electrical components. they might even be able to give you some left overs for free.not all bags work, but if you try enough, you will find the right one(s).

i once ordered some through through this local electronics store in germany >>
http://www.huebner-elektronik.de/index.php
they were called "Lagerbeutel" (leitfähig). but i'm sure you should be able to find these through a local store in the netherlands too!

together with mika satomi i'll be giving a workshop in rotterdam at V2 in mid may, if you're interested in wearable technology, you should come:-)

greetings,
hannah

[vitorls]

Hello

I´m very happy with the bend sensor you send to me.
Now I try to construct more with your very good instructable. It´s not easy because the materials is dificult to find, but i thing i can go to the end.
I go use the bend sensors in this project: http://fotocrono-fatosensivelwireless-vls.blogspot.com/
before i made a glove with a normal bend sensors, but now I made suit that i´m going to use your sensors for i read some moviments of the body. The ideia is to translate the moviments to generate sound poetry.

Thanks again
Vitor LS

Thanks a

[Plusea]

Hi Vitor!

i'm super happy that you are happy with the bend sensor!
if you are able to order materials from lessemf, then they are not so hard to get. but you can also get conductive thread from sparkfun and velostat from a local electronics store (the black anti-static bags used to package sensitive electronic components, but careful! not all work).
i love your washing up glove with bend sensors!
have you seen our puppeteer project? we also used our bend sensors to track full body movement and let the performer speak through a text with her movements >>
http://www.instructables.com/id/Puppeteer_Motion_Capture_Costume/
http://kobakant.at/index.php?menu=2&work=5

please keep me updated on how your work goes, i'm super interested.

thanks again and greetings,
hannah

[vitorls]

Hello Hannah I´m from a litlle step to find all materials to construct the bend sensor. I only miss the velostat. Of course I know your project: Puppeter. It´s because of that I discover your bend sensors. When I discover that project I´m very happy because I saw for the first time that it´s possible to do something similar to my ideia. That project its clouse to my project, and in the Puppeter project I see its possible to do. In my project the main diference going to be in the content, but maybe I go use accelerometros and gyroscopios. I go use sound poetry, disconstruct and construct again the phrases. My intention it´s try to revel one occult truth from the body language. Your project It´s became very inspirer and give me confidence to start, and for that i say thanks again! I do this for my master course and I hope you don´t mind if I make reference to your very good work. Thanks for you like my loveGlove. I will send to you my upgrades from my bloog. bye Vitorls

[techie]

I was thinking that you could have these sensors in your clothing attached to a battery powered Arduino. Then you could program it with the 8x8 led controller from Modern Device (http://moderndevice.com/) to create different patterns of leds sewn into your clothing. It could be quite interesting at night.

Great instructable!

[Plusea]

thanks for your comment. but i think you should be the one to make the LED display if you are interested in it!
have you seen leah buechley's work? she has made quite a few led matrix wearables >>
http://web.media.mit.edu/~leah/grad_work/projects/LED_clothing/tank.html

[techie]

Yes, I was using you in an indefinite sense of anyone reading the post. I am thinking of some sort of display. I just got some velostat and am anxious to create some sensors. In the dance project, did you find that the sensors fatigued over time and had to be replaced? Leah Buechley's work is quite wonderful. Thanks for the link! cheers