Flexible Fabric Pressure Sensor

How to make a flexible fabric pressure sensor from 3 layers of conductive fabric.

Step 1 Materials

You will need:
(The amounts of material depend on how large you want the touch pad to be)
- Ex-static fabric from www.lessemf.com
(also see http://cnmat.berkeley.edu/resource/ex_static_conductive_fabric)
- Stretch conductive fabric from www.lessemf.com
(also see http://cnmat.berkeley.edu/resource/stretch_conductive_fabric)
- Cotton thread or a kind of non-conductive adhesive

Optional:
- Another material as padding on either side. In the example I'm using Neoprene (ordered from Sedochemicals)
- An LED to show it works
- Energy source. In the example I'm using 3x1.5 Volt batteries
- Cables to connect

Comments

[cuzzea]

Hi, I really like this and would like to try it my self, but can't find stores that sell this kind of fabric in Europe (I'm from Romania), do you know any?

[Plusea]

there is plug and wear in italy >> http://www.plugandwear.com/
and MUTR in england >> http://www.mindsetsonline.co.uk/index.php?cPath=418_6_572

[Hybrid.Bruce]

Hey worked like a charm, but is there anyway to make it light up when theres a certain size point applying the pressure and not when all or most of the pad is being pressed or will that require a computer program?

[Plusea]

yes, you could use a small microcontroller to translate sensor values into the output values you want. or you can also try tailoring the sensor to the exact range that you need. i have found that by minimizing the conductive surfaces on either side of the piezoresisstive material, i can adjust the sensitivity of the sensor.
>> http://www.kobakant.at/DIY/?p=65

[ivsfl]

I need to make a switch to be placed in a chair cushion. Would you recommend for this application? Reliability and durability is important.

Thank you

[Plusea]

for a simple fabric switch, i would use the following fabric pushbutton instead: http://www.instructables.com/id/Three-Fabric-Buttons/

[haunted.haunt]

How do you make it on a large scale?

I want to make ti the size of a standard "Welcome!" mat.

Is there a difference?

[Plusea]

try it out! but i think the design should scale quite nicely. you might want to add an extra layer of perforated foam as a spacer to keep the conductive and piezoelectric layers totally separate when nobody is standing on it.
also, this is a rather old Instructable, be sure to look at some of the newer designs:
>> http://www.instructables.com/id/Conductive-Thread-Pressure-Sensor/
>> http://www.instructables.com/id/Pressure-Sensor-Matrix/
>> http://www.instructables.com/id/Flexible-Fabric-Pressure-Sensor/

[Mike Nelson]

Hey, so would it be possible to relate the "pressure" / amperage to weight or maybe a weight range? like < 40 pounds or >= 40 pounds? Thanks,

[B.F.L.M]

Would i have have to increase the amount of power if my pad is rather large with very long wires from the pad to the power source and led?

[Plusea]

if you pad is large.... then you might loose power if you're detecting pressure that is happening far away from where you attach the wires to the pad. to solve this you can make multiple contacts from the wires to the conductive fabric surfaces on either side of the ex-static.
if you are you are using "wire" and not conductive fabric or thread for the long (how long?) connections then you should be fine.

also check out the following instructable:
>> http://www.instructables.com/id/Conductive_Thread_Pressure_Sensor/
i've had better results with the velostat (or eeonyx fabrics) than the ex-static fabric.

[B.F.L.M]

the long wires im talking about are the ones that connect the pad to the batteries and LED Ive talk to a couple of electritians and they say that it does not matter Thanks for the advice :)

[cantthinkof bettername]

You could take apart a controller and make a dancepad

[Graceria]

I love this instructable, but I have a question. Do you know what the maximum amperage this sensor can handle is? I'm looking into the possibility of using these as part of a costume for which I would want them to be switches to activate a set of animatronic wings and I need the switches to be able to handle 4amps. Can you tell me if this design can handle that?

[Plusea]

i've only ever tried it with low amperage. best thing would be to test it. you can order a sample kit from LessEMF that contains all the materials you'll need, if you don't already have some of the materials to test it with. let me know how things go. and maybe if someone else had experience or knowledge? - let us know!

[myrtou]

(removed by author or community request)

[wupme]

About 5-10 working days (i'm also from europe, and order pretty often stuff from the USA) If it takes longer, blame the Customs.

[myrtou]

thanx! 10 days is not bad

[Plusea]

Hello,
ive actually done some more recent versions of this pressure sensor. you can see pictures of them here: http://flickr.com/photos/plusea/sets/72157607328386559/
and this is a similar Instructable: http://www.instructables.com/id/Analog-Fabric-Joypad/

since these more recent versions use stitches of thread, rather than a full surface of conductive fabric, i could imagine stitching in such a way that allows quite a lot of transparency. neoprene and other squishy materials are great for the force feedback of a pressure sensor. one could also use silicone or rubbers. as for the layer of Velostat/piezoresistive material inbetween... i'm not sure of a transparent version of this. there are ways one could also cut holes in this to make it somewhat transparent.

i'm actually located in both america and europe so that i order things from the US to my american address. i don't know how long it takes to europe, but i would expect them to be quite fast, not more than a week or 10 days.

what are you working on? i'd be interested to see some pictures.
good luck and fun!

[mrmath]

There's no way to get x/y data out of this, right?

[Plusea]

correct. but
i was also thinking maybe if you set 3 or 4 points where you meassure the current flowing then you could do a callibration by pressing on different points of the surface and saving the different (if they are different) results from each of the points and then in future you could track where the preassure is being appied by comparison.

what i like about this touch pad is that both how hard you press and how much surface you cover influences the resulting current.

i want to implement it in future in a "massage gamepad" http://plusea.at/mme.php because inbetween the layers of neoprene it responds nicely to both light touch over a large surface and strong pressure applied to small areas.

[endolith]

And you did:

http://www.instructables.com/id/Analog-Fabric-Joypad/

[zachninme]

You could probably measure resistance... But thats way to unreliable, so probably no ;-)

[Plusea]

yes. though what i'm aiming at is just to get a value above a maximum threshold (minumum resistance) for a simple input.

[mrmath]

I was thinking that if you wanted some crude x/y, you could create a matrix of strips. The top layer going horizontal and the bottom layer going vertical. Then, of course, when you press, you get measurements across a set or two, and presto, you get x/y. It would be very crude resolution, but it could work. Not that you need x/y readings. I think it's a fine instructable as is, and if this is what you want, then it's perfect.

[andy]

It would be time consuming though to get fabric strips like that, though it would work rather well, unless the contact area was greater than one strip, which would confuse a resistance based method of output and could confuse a pic through strange data. But it would look cool outputted via a matrix of LEDs, or even just one per strip or the like. Instead you could put a contact across the middle of the pad, and on two opposite edges of the opposing pad put two contacts. Then use an Op-Amp as a differential amplifier and the output would be the difference between the two contacts (in resistance, and so distance and _not pressure_ (it would measure a single point of contact correctly, but not more than one)). The whole method does rely on the material having some readable resistance from the OpAmps perspective thought, anyway, just some thoughts hope this helps, Drew

[andy]

p.s. to get X and Y stack two of the moduals described and turn one 90 degrees to the other. One output for x another for y. --Could work instead of scroll wheels or joysticks if properly tuned... should be easy enough given that if it is tuned once (say with a couple of trim pots) then it will remain tuned for any given construction of the same dimensions and material properties. Good luck with your project, hope this helps. drew

[TamarGirl]

Hi Plusea, I'm not normally thick, but I've read this through to the end and I don't get it. What is it for? How would you use it? Why is it connected to a power source? What will the power source do to it? I guess you'd get that I don't know a great deal about electronics!!! Judanne

[hump]

TamarGirl,

I am looking into this topic for the creation of pressure sensitive mats which I can place in the desert sand next to some surplus company assets which are being stolen for their scrap or salvage steel weight, at about 11 to 1,200 pounds each. So I create these mats, from a rubberized, water and element proof material, and place them and cover them over with about an inch of sand -- and when a criminal approaches their target to hook it up to their portable hoist -- they compress the mat and complete the circuit = which is connected to either a loud siren and intense strobe light, etc. Or even some sort of non-lethal concussion device which is also buried in the sand next to the asset, and with respect, either the Security personnel is alerted by the noise, and or, the bright light(s) -- or the criminals can no longer perform their work on the private property in which they have NO UNDERSTANDING of the concept of; *Keep Out* *No Trespassing*, etc. = so they stumble away trying to figure out what just happened to their sorry butts.

Now, I would normally go with an attached trip-wire to set off one or the other types of support devices -- but the difficulty there is in lifting the asset and finding a place to tie the wire up in a way in which no one can easily see it and disarm it before moving the asset; so the pressure mat does Not have to be attached, and can be completely covered by the natural desert materials, and can be placed where the criminal can't even lay his hands on the asset before setting OFF the switch that completes the Security protection circuit. And on the other side of the coin; the circuit can trip a Silent alarm which brings me out to make the Arrest while they are still working on their theft. That one is my favorite, over circuits and systems that will only scare them off. The Arrest(s) make more noise on the local news and has the possibility of warning other criminals or crews that the risk of capture is just too great in a particular territory.

So there ya go. An example use of the concept, if not the actual materials mentioned in this article. I'll most likely locate, or create my own conductive materials for the pressure mats I require to put a stop to the near constant criminal attacks in my territory. Any existing products already on the market are absurdly over-priced which knocks those sellers right out of our security budget.

Thanks for your time.

[Plusea]

Maybe it is a bit hard to understand because there is no specific use for it. It is basically a way of making a soft and flexible pressure sensor purely out of fabric. The Instructable is just a demo of how it works. You have a power supply and an led and by pressing the layers of fabric (conductive and ex-static) together you are decreasing the resistance and therefore are regulating the ammmount of electricity flowing to the led. If you see my other Instructable Massage me Jacket you will see the implementation of this simple principle.
Does that make it any clearer???

[TamarGirl]

Yes, thanks Plusea. I saw your previous instructable and thought that would make good interactive wearable art. Got it now! Judanne

[joshkay]

I found this link here which might be useful for people interested in combining XY with pressure sensitivity in fabrics

http://xyinteraction.free.fr/wiki/pmwiki.php/Site/Concept

I'm personally starting with hardware, but moving on to fabrics very soon by the looks of it.

[RiddleOfSphinx]

This would be nice for what I need, laptop touch pads are so friggin tiny :P

[LasVegas]

Did you order the Fabric Sample Kit from LessEMF? Other materials look like they may work just as well at a lower cost. My concern is the resistance over a larger area and the complexities of connecting wires permenently that will resist multiple washings.

[Plusea]

Yes, we first ordered the sample kit from LessEMF and then we ordered more of the stretch-conductive and the ex-static fabric. We needed the fabric fast and were hoping to find a supplier in Europe but couldn't. If you know of any, or any cheaper competitors, would you let us know. That would be great!

We also ordered sample kits from a few Chinese companies, that arrived but did not contain a stretchy conductive fabric.

And yes again to wire connection. So far the best result has been to use iron-on sheeting (a kind of fabric glue) to connect the wire to the conductive material (sandwiched between), but it is not really optimal. We've now got some samples of conductive thread from www.bekaert.com and want to see what other solutions we can come up with.

We had problems with the resistance over a large (about A4 size) surface with some of the other kinds of conductive material, but not with the stretch-conductive so far.

[LasVegas]

It's odd that we both have been working on similar projects... I've been working on various solutions for a flexible switch that could be used within a garment and remain washable. So far without any real luck. Your solution looks very promising. The punched foam in your other instructable was the very technique I've been working on, but foam's a problem with washable garments. I'm going to order LessEMF's sample kit and do my own experiments concerning my application. Thanks! You've given me renewed hope! :)

[llama lord]

were would i get the fabric?

[Plusea]

We ordered the stretch conductive fabric and the ex-static fabric from www.lessemf.com but there are many other suppliers out there, especially in China. The Neoprene we ordered from www.sedochemicals.de.

[dlamblin]

I don't wish to be negative; but I feel this is a case of "buy the product; use as directed" I feel as though instructables needs an offshoot to categorize and collect "cool non-end-product products"

[Plusea]

I don't quite understand. do you mean that the instructable sounds a bit like an advertisement or that the outcome is not an end-product?