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Stitching conductive thread into neoprene to create a pressure sensitive pad. This sensor is very similar to the Fabric Bend Sensor or vis-versa. And also close to the Fabric Pressure Sensor, but the difference is that the conductive surface is minimized by stitching only a few stitches on either side with conductive thread. This creates a good fingertip pressure range.

The resistance range of these pressure sensors depends a lot on the initial pressure. Ideally you have above 2M ohm resistance between both contacts when the sensor is lying flat. But this can vary, depending on how the sensor is sewn and how big the overlap of the adjacent conductive surfaces are. This is why i choose to sew the contacts as diagonal stitches of conductive thread - to minimize the overlap of conductive surface. But only the slightest touch of the finger will generally bring the resistance down to a few Kilo ohm and, when fully pressured, it goes down to about 200 ohm. The sensor still detects a difference, right down to about as hard as you can press with your fingers. The range is non-linear and gets smaller as the resistance decreases.



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

As in all my Instructables 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. But they also ship to Europe within about 10 days.

Velostat is the brand name for the plastic bags in which sensitive electronic components come packaged in. Also called anti-static, ex-static, carbon infused 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, so test them first!)

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.
 
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Step 1: Materials and tool

Picture of Materials and tool
MATERIALS:
- 1.5 mm neoprene from http://www.sedochemicals.de
- Conductive thread from www.sparkfun.com
also see http://cnmat.berkeley.edu/resource/conductive_thread
- Stretch conductive fabric from www.lessemf.com
also see http://cnmat.berkeley.edu/resource/stretch_conductive_fabric
- Fusible interfacing from local fabric store or
also see http://www.shoppellon.com
- Velostat by 3M from http://www.lessemf.com
also see http://cnmat.berkeley.edu/resource/velostat_resistive_plastic
- Regular thread
- Machine poppers/snaps

TOOLS:
- Pen and paper
- Fabric scissors
- Iron
- Sewing needle
- Popper/snap machine (handheld or hammer and simple version)

Step 2: Create your stencil

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Decide on a shape for your pressure sensor. Consider that you will need to create two separate tabs for the two layers of conductive fabric and that these should not touch each other (see pictures). Sketch the shape for your sensor onto some paper or cardboard, including both tabs. You will also want to plan where to make your conductive thread stitches in the center or the sensitive area of your pressure sensor. One stitch is the minimum and the more stitches the more sensitive your sensor will be, in the sense that you will hit the least resistance with much less pressure. So best to do as few stitches as necessary to evenly cover the area you want to cover.

Step 3: Prepare your materials

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Trace your stencil onto the neoprene twice and cut both out. And trace the stencil once onto the Velostat, but cut out the shape from the Velostat 2-3 mm smaller than the stencil and don't include the tabs.

Cut two small pieces of conductive fabric the size of your tabs or slightly smaller and iron these on to the neoprene with the fusible.

Mark with a fabric pen or a permanent marker where you will be stitching with the conductive thread. Make sure the markings on each side are identical so that when you lay both sides on top of each other the identical stitches are sure to cross each other in an X like manor and not match up. This way each two stitches will be sure to cross each other and make direct contact in only one point.

Step 4: Sew your stitches

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Take the conductive thread single and stitch into the neoprene from the back so that the knot stays on the outside of the sensor. Now stitch your stitches but there is no need to go all the way through the neoprene so that they are visible and vulnerable on the outside. You can dive into the neoprene and at the same time this isolates the conductive thread. When you have finished you stitches you will want to bring the thread to the patch of conductive fabric that is fused to the tab. If you plan ahead you can aim to end close by. With about 5 to 7 stitches attach the conductive thread to this patch and then cut it.

Do the same on the other side of neoprene.

Step 5: Sew things together

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Layer your piece of Velostat between the two pieces of neoprene with the conductive stitches facing inwards. Thread a needle with regular thread and sew around the edges. Do not sew too tight or you will have high initial pressure. If you want to increase the resistance, lower the sensitivity then add one or two or more layers of Velostat in between.

Step 6: Poppers

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Read the instructions on how to use your popper machine. Attach a female popper to one tab and a male popper to the other tab, preferable facing the same side. Make sure that the popper goes through the patch of conductive fabric. This way it is connected with the conductive thread stitches.

Step 7: Visualizing

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To see how your pressure sensor works we will need to include it in a simple electronic circuit.
If you happen to be working a lot with poppers and circuits you might like to modify a set of crocodile clips to have poppers on one end. Otherwise you can just clip on to the poppers.

To visualize with a multimeter, create the following setup (see pictures)
Set multimeter to measure resistance (in Ohm).
Multimeter plus to one side of fabric pressure sensor (doesn't matter which side) and multimeter minus to other side of fabric pressure sensor. Apply pressure and watch the resistance value change. You might have to adjust the range if you don't see anything. If you have a constant connection then either you forgot to put the Velostat in between or somewhere your two pieces of conductive thread are touching. Ops.

To visualize with an LED or vibration motor, create the following setup:
Connect the plus of two AA batteries or a 5V source to one side of the pressure sensor (doesn't matter which side) and connect the other side of the pressure sensor to the plus of an LED or either side of the vibration motor (switching plus minus only affects the direction of the vibration motor, whereas an LED only works in one direction). Connect the minus of the LED or the other other side of the vibration motor to the minus of the power supply.
Apply pressure to the fabric pressure sensor and control the brightness of the LED or the strength of the vibration.



In the video I have hooked up the pressure sensor to an arduino (www.arduino.cc) and am visualizing the change in resistance with a simple application written processing (www.processing.org).

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

ENJOY!
trodd1 year ago

Hi I am looking into doing a project with sensors like these which type of audino did you use? or is there another alternative taht can be used?

Vaelk2 years ago
Greetings Plusea,

Interesting post, but I was wondering, can this sensor be used to light a set of LED's?

Thanks in advance.
One for all2 years ago
Cool stuff. I was wondering if you could rig one of these in such a way that it could act as a switch for a mechanical device. Something that will allow you to say...trigger a compression spring (depending on the amount of pressure applied and time elapsed). Thanks!
nattyclem3 years ago
I like think this is great and I think it looks cool aswell.
Can I ask what program you are using on your computer in the video?
Plusea (author)  nattyclem3 years ago
Hello Plusea

Is that possible to measure big load in this system?

Thanks
loort4 years ago
Hey there,
I was wondering if you were going to create a number of smallish, closely spaced sensor buttons that are arduino interfaced, would you recommend using the conductive thread method as per here, or the conductive fabric sensor as in your other instructable? which would be more flexible and which more durable?

Really cool instructable.
Plusea (author)  loort4 years ago
whether you choose conductive fabric or thread influences the sensitivity of the sensor. the larger the conductive surface (fabric = large, thread = minimized) the more sensitive it is. i would recommend using thread. but fabric will also work.
 it is really a gr8 work
i want to ask about how to make a pressure sensor to stop an alarm
My idea is to make a carpet with an alarm ( it's really hard to wake up everyday at 5:00 am to go to college) and this alarm will not stop unless i'm standing on this carpet

hope that someone can help me through this quickly :)
Plusea (author)  shereen hussein5 years ago
yes, the pressure sensor might be good for this project because you differentiate between pressing down on the carpet with your hand or standing on it with your full body weight. if you wanted to just push on the carpet with you hand, then you could construct a fabric on/off button. with the pressure sensor you'll need to set a threshold, above (or bellow) which it will stop the alarm. and you can set this threshold to be for full body weight. the velostat sensors are good for this.
 thanks for your reply
zyzar5 years ago
It's impressive and i would love to try.. but may I ask..for stretch conductive fabric...do I have to order online only or is there available in the market???
Plusea (author)  zyzar5 years ago
i only know of online distributors in the usa, uk and italy. but all of them will ship abroad.
lessemf.com
mutr.co.uk
plugandwear.com
B.F.L.M6 years ago
can this pressure sensor be "inlarged" like the one in your other instructable? how strong is this electricity conductive thread? Can it be used for something like a trip wire? I think these 'ibles are great, and they help open the door of imagination with this kind of thing From tripwires to 'whiteboard'-like programs, these ibles are the place to look for ideas!!
Plusea (author)  B.F.L.M6 years ago
for sure it can. you just need to find a nice way to sew the stitches of conductive thread to cover the surface area you want to be sensitive. see the following JoyPad as an example:
>> http://www.instructables.com/id/SZED352FC2EFZ6V/

not sure it the thread is strong enough for trip wire. it does not rip to easily but it does. you can get stronger conductive thread from lame life saver in canada:
>> http://members.shaw.ca/ubik/thread/
or in the uk from mutr:
>> http://mutr.co.uk/

what are you devising?
the best solution is always to just try it out.
SNYG Plusea5 years ago
Halo Plusea
Can I talk to you on the phone
B.F.L.M Plusea5 years ago
im going to try to make a pressure pad that fits under a carpet that is 186x29
would it be necessary to make multiple 'contact points?'
if so, can i connect all the positives to one wire and negatives to another safely?
i really appreciate all of you help :)
Plusea (author)  B.F.L.M5 years ago
inches or cm? multiple contact points might be good and yes, they can all be connected together safely. the conductive thread can't take more current than that of about three 1.5V AA batteries. with a 9V battery it tends to smoke. instead of conductive thread you can also use aluminum foil...
Could this be modified into a normally closed sensor so that it senses when pressure is removed?
Plusea (author)  willowtaylor5 years ago
using a microcontroller you could program it to react to a decrease in pressure no problem. but to have the resistance decrease as pressure is applied - you'd have to come up with some kind of physical contraption that flips the application of pressure maybe.... or find a material that reacts opposite to velostat. why do you need it to be this way?
What I actually need the device to act as a simple NC on/off switch.
Plusea (author)  willowtaylor5 years ago
well if you need a switch, then maybe the fabric button is more suitable:
>> http://www.kobakant.at/DIY/?p=48

right now i have no ideas of how to make it into a NC switch though.....
DaemonMaker6 years ago
I'm not familiar with the various qualities of neoprene offered on the SedoChemicals site. What quality do you suggest?
Plusea (author)  DaemonMaker6 years ago
on the www.sedochemicals.com website click on "product" --> "technical data / neoprene" and then they have links to all the different qualities.
LS is super soft and HHS is much tougher and less "squishy" but still quite soft. S and HS are in between. NF i have never tried and W just means that is their white neoprene.

for my sensors i have been working with S and HS mainly. but LS and HHS would work too. hope this helps.
Your explanation is far more useful than the tech specs given that I'm new to neoprene, thanks! I'm assuming that you are using nylon for the lining, is that correct?
Plusea (author)  DaemonMaker6 years ago
great. it also took me samples of all the qualities to really know the differences by feel. yes, i order my neoprene with "nylon/polyesterjersey standard" lining on both sides.
zephyrbunny6 years ago
I love your projects. You've totally inspired me to venture into the soft sensor world too. Here's a video of a Fleece Bunny Pressure Sensor I just made today. I'm thinking of making a bunch of different animals.

I made the little sensor and then a second "jacket" to put over it to cover the exposed thread (fleece isn't thick enough to thread inside). And so you couldn't see the two tabs separately.

Thanks for posting this instructable!
Plusea (author)  zephyrbunny6 years ago
Thanks so much for the comment. I saw your video and it is very cool to see my Instructable realized by somebody else!!! Felt might be another material that is thick enough to sew inside, though your jacket solution also does the trick. Any ideas on what you might use your pressure sensitive animals for, other than LEDs? I'm very much looking fwd to following your works. All the best!
I always enjoy seeing other people's versions on my stuff too = )

I'm kind of interested in getting the different animals to create drawings in processing (so pressing the bunny draws different sized bunnies depending on how hard you're pressing). But I'm pretty new at all this and still have to learn how to get processing to even read from the arduino.

Another idea I want to try out is making a pressure sensitive yoga mat. I'm not sure what it would control, maybe some lights or drawing or music. I just think it would be fun to use yoga/pilates to make stuff. I'd love to hear any tips/ideas you might have for it.
Plusea (author)  zephyrbunny6 years ago
Hey, yes, nice ideas!

I actually made a pair of slippers with these pressure sensors embedded and then wrote a little drawing application. reading the analog input from the arduino into processing is super simple and leads to lots of ideas. here is the JoySlippers Instructable and in step 6 there are links to downloading the arduino and processing code that i used for my simple drawing application.

When i showed the JoySlippers at the maker fair last april, a lot of people said that it would be a great idea for visualizing yoga moves.... but i don't do yoga myself, so i never picked up on it and i'm definitely interested to see what you can make out of it!

i'm also interested in sound output, because visuals always require you to look at something. though i'm more of a visual person myself and have never really worked with sound before....

keep me updated:-)
hahahah, lol, all the related ibles belong to you!

and they're all featured....

*jealoussyyyy*
Plusea (author)  AnarchistAsian6 years ago
Oh wow. probably because i tag a lot of them with similar words. Instructables is such a great place to post ideas and get good feedback. I think that is why i ended up posting four of them this weekend:-) because i don't know where else people look for these kinds of things?
huh, yeah, i doubt people often search "fabric sensors" on google...

but since this has been featured, more people will know about it!

i'm currently working on a coil gun, and will post an ible... this could take a while...
Also all but one is featured.
yeah, impressive...
"fabric sensors" on google... You would be suprised. There is a massive craft following.
oh my...
Lftndbt6 years ago
WoW!! You continue to amaze me. Nice work once again. You have inspired me to contribute to this new fabric following. I'm almost finished my first effort. Thankyou.