Instructables
Picture of Pressure Sensor Matrix
3159580934_7fde519f5c.jpg
3158747953_1c7b35ccd0.jpg
3158838785_f97f764aa0.jpg
3159675230_229d5a1569.jpg
3158845319_7f9fa916c9.jpg
Four separate pressure sensors not only give feedback about where I'm pressing, but also how hard. The sensitivity is ideal for finger pressure. Though it is not linear, it is stable. Very sensitive to light touch and then it takes a lot of pressure to reach the minimum resistance.

The inside looks just like the fabric pressure sensors, except each stitch is connected to a separate conductive fabric tab. The downside is that separate tabs and connections to these tabs take up a lot of space, especially if you want to achieve a tight matrix of sensors. A grid of lines and columns and some code to analyze these (separately power and measure) would allow for much tighter spacing. This version is nice because it is so simple.

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.

Video


Video


This Instructable covers two slightly different versions of the pressure sensor matrix. The only difference being the spacing of the individual pressure sensors in the matrix. In one of them they are placed practically next to each other (white) and in the other there is a 1cm space in between each sensor (purple), but because of the thickness of the neoprene it is not possible to press in between the sensors without pressuring a sensor. Hope this makes sense.

I am also selling these handmade Thread Pressure Sensors via Etsy. Although it is much cheaper to make your own, purchasing one will help me support my prototyping and development costs >>
http://www.etsy.com/shop.php?user_id=5178109

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 bags... 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, but at the moment EeonTex conductive textile is only available in a minimum of 100yds. But try ordering samples!

I chose to work with neoprene because it offers a form of natural force-feedback and also it is great for sewing into with the conductive thread and thus isolating it. But you can easily replace the neoprene for some regular stretch or non-stretch fabric and even try felt or kind of rubber.
 
Remove these adsRemove these ads by Signing Up

Step 1: Materials and Tools

Picture of Materials and Tools
MATERIALS:

For sensor:
also see http://cnmat.berkeley.edu/resource/conductive_thread
also see http://cnmat.berkeley.edu/resource/stretch_conductive_fabric
  • Fusible interfacing from local fabric store or
also see http://www.shoppellon.com
  • Regular thread

For reading input into your computer and running an application that visualizes the changes in resistance:

TOOLS:
For sensor:
- Fabric scissors
- Sewing needle
- Iron
- Fabric pen that disappears over time
- Pen and paper
- Ruler

For reading input into your computer and running an application that visualizes the changes in resistance:
- Soldering station (iron, helping hands, solder)
- Knife for cutting perfboard
- File for filing edges of perfboard

Step 2: Cut stencils

Picture of Cut stencils
3158748997_06a0610447.jpg
3159362472_ca0e961f9f.jpg
If you don't want your sensor to look the example then you will have to decide on a shape/design of your own and create your own stencil. Otherwise you can download the stencil here >>
http://farm4.static.flickr.com/3121/3159362472_ca0e961f9f_b_d.jpg

Cut out the stencils from paper and trace on to your neoprene (or other fabric) and Velostat. You will need one square of Velostat that is a few millimeters smaller than the smaller piece of neoprene. You can use 2, 3 or more layers of Velostat to make the sensor less sensitive to light touch.
Cut out the fabric.

Step 3: Ironing conductive fabric tabs

Picture of Ironing conductive fabric tabs
3159586610_dd647f4306.jpg
3159590070_76bab06bbf.jpg
3158757819_4216d4a629.jpg
Take a small piece of stretch conductive fabric and fuse some fusible to one side of it. Cut into 5 small tabs and fuse (iron-on) along one of the shorter edges of the slightly larger piece of neoprene.

Step 4: Sewing conductive thread

Following the instructions on the stencil sheet, sew with conductive thread (take it single, not double) into the larger piece of neoprene, coming in from the side with a knot in the end of the thread, making one visible stitch and then sewing inside the neoprene to the appropriate tab. Stitch to the tab with a few small stitches and then plunge into the neoprene one last time and then just cut the thread and dont worry about knotting this end.
On the smaller piece of neoprene youll have all four stitches connected and then you have to sew the end of the conductive thread to the appropriate tab on the other piece of neoprene.

!!!
All this time make sure that non of the stitches are touching inside the neoprene. Do not cross them. Follow the stencil!

Step 5: Sewing together

Picture of Sewing together
3159675230_229d5a1569.jpg
3158838785_f97f764aa0.jpg
3159671982_6a75c6f3e4.jpg
3158829795_2992240889.jpg
Place the piece of Velostat in between your two pieces of neoprene, conductive stitches facing inwards. Sew around the edges with some regular thread. You can even leave the edge with the conductive tabs open and this way you can change the layer(s) of Velostat.

Step 6: Pull-up resistors

Picture of Pull-up resistors
3169507325_c7606f19b5.jpg
3170337404_51196d61f0.jpg
3341036327_69e6163dab.jpg
Test first:
Hook up a multimeter in beep mode to the VCC tab and in turn connect it to each of the other tabs. Without even pressuring it, make sure it does not beep. If nothing is touching, then you can pressure each sensor individually to see its resistance range.

Update: The resistiance range of this sensor is ideal for the internal 20K ohm pull-up resistors of the Arduino. So you can skip the rest of this step and look for the right code to activate your internal pull-ups in the next step.

Cut a small piece of perfboard with conductive copper lines, at least 6 x 6 holes big. Solder as seen in schematic illustration and plug in to your Arduino board. For more information on pull-up resistors and why they are necessary, follow this link >>
http://cnmat.berkeley.edu/recipe/how_and_why_add_pull_and_pull_down_resistors_microcontroller_i_o_

Clip the crocodile clips to the correct conductive tabs of your pressure sensor matrix.

Step 7: Run application

Picture of Run application
For Arduino microcontroller code and Processing visualization code please look here >> http://www.kobakant.at/DIY/?cat=347

Program the Arduino and run the Processing application, and if everything works you should be able to see your sensor input being visualized through the graph and drawing options. See videos in the intro step.

Let me know if you have any problems.
And enjoy!
windrago3 years ago
the links are dead - do you have the code somewhere else?
thx!
Plusea (author)  windrago3 years ago
check these links here: http://web.media.mit.edu/~plusea/downloads/code/

sorry for the inconvenience!
mcti Plusea28 days ago

Have you updated this link? I am told I don't have permission to view this page. Thanks!

omtinole Plusea2 years ago
Which of these is the 2x2 matrix visualization code? The file names are rather cryptic.
Plusea (author)  omtinole2 years ago
good point. i have tried to start organizing my code better. please see this link: http://www.kobakant.at/DIY/?cat=347
and check back by the end of next week.
swoudlxy4 months ago

Hi Plusea,

May I ask what is the power consumption for each pressure sensor? Many thanks for your help.

BadPuns8 months ago
I was wondering if you could be bothered to write or direct me to an in-depth tutorial on connecting this to an Arduino or Raspberry Pi?
Plusea (author)  BadPuns8 months ago
here is a good tutorial >> https://www.sparkfun.com/tutorials/389
BadPuns Plusea8 months ago
Thanks a lot. I don't have an Arduino yet because, strangely enough, my parents don't trust me plugging things in and downloading stuff on their computer. I don't know why they wouldn't trust me, of all people...
khetarpal9 months ago
Hi Hannah,

Thanks for sharing this. I have learnt a lot from your instructables. I'm working on a creating a pressure map for a healthcare application. Would be great if you could elaborate on Velostat vs Eeonyx fabric pressure sensitive properties. I understand that sewing convenience / stretching capability are obvious benefits of using Eeonyx, but what about the pressure sensing range & electrical properties. Does Eeonyx provide a more linear resistance signal when changing pressure? Does it have less hysterisis compared to Velostat?
daleruisky11 months ago
Thanks so much for putting this together! Your links to the companies selling the materials is invaluable; saved me hours of research. Keep up the great work!
vijayrex1 year ago
Hi, i have a doubt. How do i get the visualizing in the processing? I have both of ur arduino and processing codes. Uploaded the arduino code to the UNO board using Arduino software and when i try to run the processing code in "processing" software it just opens a small blank window.. Can you please help me?
agomes62 years ago
amazing work! you're an inspiration for all of us!

I have one question one the fusible material....is there a specific one you'd recommend or this should do it?:

http://www.shoppellon.com/products/803-800-clear-fuse.aspx

Thank you for your wonderful input in this community!
Plusea (author)  agomes62 years ago
thanks for your comment! while i have not used this particular pellon product, from the description it looks like it will work for fusing (heat gluing) two pieces of fabric together.
agomes6 Plusea2 years ago
not particularly this instructables but...success :)

http://img535.imageshack.us/img535/7141/54182547503376585865718.jpg

your kits are fun! following up on your work for a workshop proposal quite soon (ACE). you're the best ! thanks
Plusea (author)  agomes62 years ago
thank you so much for this comment and for sending the picture. it is so nice to see what becomes of the kits once they are shipped to people! i hope things worked well for you. i'm always grateful for any feedback on how to improve them.
:-)
agomes6 Plusea2 years ago
no problem!

this one (several of them actually) were sitting around at my lab and I recognize them as being yours :)

I think this one is neat as is, no improvemente needed :)

Note to unexperienced users with sewing related materials....neoprene cannot be ironed (or not directly anyways...I know that now :) ) good luck with all your future work, I'll look forward to keep following it
scanlinj072 years ago
Great work...I was curious if there was a way to build this so that the information from the analog function (stepping on or pressing the mat) can be stored and then extracted later, like after a day, to view on the computer? So basically it would store the activity of how many times is was pressed and for how long and then that data would be stored and viewed after a period of time?
shall63 years ago
Is it possible to adapt this to handle high impact? I'm looking into making a body suit for sports-impact analysis.
windrago3 years ago
thanks super Plusea, you rock my fabric-world!
egasimus3 years ago
Hi there. First of all, I can't help saying that I like your work and I'm always glad to see a beautiful and ingenious girl in the field of DIY electronics. Keep up the good work! Compliments aside, can I still order samples from Eeonyx, and would they ship to Eastern Europe? I saw no mention of that on their site, and I'd really like to have EeonTex on my hands. The possibilities with that stuff are endless.
atomanttan3 years ago
Hi Plusea, your work is very interesting.
If I have a bigger pad and higher resolution, do you think I could use it as a pressure sensing seating mat? Do you have any pressure sensor matrix in stock at the moment as I could not find it at etsy. Thanks :)
Plusea (author)  atomanttan3 years ago
try it and see if it works. in general the velostat pressure sensors scale nicely.
here is a link to the kit on etsy:
>> http://www.etsy.com/listing/51675531/fabric-pressure-sensormatrix-kit
max05064 years ago
can you also make like a realy big one whith realy small touch squares to use it as a mouse/ touch pad for your pc.
Plusea (author)  max05064 years ago
yes you can and you can use a teensy board instead of the arduino (but still use arduino to program it!) so that you can fake mouse input directly! >> http://www.pjrc.com/store/teensy.html
aringe4 years ago
Currently using this design as a basis for my senior design project. I'll upload it once we finish.
pstretz5 years ago
This gives me a great idea for a midi controller pillow that would generate ambient music to help you sleep. It could change as you move your head.
john otto5 years ago
Your instructables are top notch and always innovative.Thanks... I'll be watching to see what else you whip up.
ste54425 years ago
Hi Plusea, nice work!
I can see all kinds of applications for this such as shoe insoles which can react to foot pressure and adjust accordingly, office chairs which can change shape based on how much pressure you place on each butt cheek etc etc!
I might just make one of these!

S

PCBPolice
NachoMahma5 years ago
. Another great one from Plusea. How long can you keep this up?
techie5 years ago
This is another excellent idea. I made a glove for a theatre project with push buttons attached to the palm to turn on lights built into the costume. This sensor setup could be a really fantastic way to do the same thing but more subtly with the lights responding to the amount of pressure. Totally cool!
PS1185 years ago
Another amazing project! Sweeeeet! BTW, when are you going to make a fabric came controller? That woud totally rock! (Yeah. I say that as if your other projects haven't 'totally rocked'. ) I'm yearning for the PlayStation blankey, myself. :)
Plusea (author)  PS1185 years ago
you mean game controller?
one of my first Instructables was for "Massage me", which is essentially a wearable game interface for back massage >>
http://www.instructables.com/id/Massage-me-Jacket/
website >> http://www.massage-me.at/
let me know what you think.

thanks for the comment!
RPisces5 years ago
This is very nice, and creative. You should seriously consider emailing the Arduino.cc admin and asking them to place this in their tutorials section; they'd love it.
Sparrow155 years ago
What if somebody wrote a program that used this sensor? Basically, where you press could correspond to a pitch, and how hard could correspond to how loud. I think this would be an awesome instrument.
fwjs285 years ago
WOW..thats is so cool! 5/5