Flexible Fabric Pressure Sensor

Intro: Flexible Fabric Pressure Sensor

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

This Instructable is somewhat outdated. Please view the following Instructables for improved versions:
>> https://www.instructables.com/id/Conductive-Thread-Pressure-Sensor/
>> https://www.instructables.com/id/Flexible-Fabric-Pressure-Sensor/
>> https://www.instructables.com/id/Pressure-Sensor-Matrix/
>> https://www.instructables.com/id/Stickytape-Sensors/

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

STEP 2: Layering

Layer you materials as follows:

TOP
(- Optional layer or neoprene)
- Stretch conductive fabric*
- Ex-Static conductive fabric*
- Stretch conductive fabric*
(- Optional layer or neoprene)
BOTTOM

*VERY IMPORTANT:
Layer the Stretch and the Ex-Static conductive fabric so that the layers of Stretch DO NOT touch!
The layers of Stretch conductive fabric should be displaced from one another in opposite corners (so that later they can both be sewn into place without the thread ever passing through both Stretch conductive layers at one time) and sticking out slightly at opposite ends (so that later on they can be connected to a power source and electric components).

STEP 3: Sewing

Now that the layers are in place, carefully sew around the edges making sure never to stitch though both Stretch conductive layers at the same time.

This step can be tricky and you can use either a sewing machine or sew it by hand as in the example.

STEP 4: Setup

This setup demonstrates how that applying pressure to the touch pad changes the brightness of the LED.

- Connect one of the (sticking out) Stretch conductive layers to the + pole of your energy source (4.5 Volt)
- Connect the + pole of the LED to the other (sticking out) Stretch conductive layer
- Connect the - pole of the LED to the - pole of your energy source
- Apply pressure to the touch pad

The amount of current changes depending on the amount of pressure to one point and the area of pressure.

Comments

[Astro01]

Nice project, I will try this! One question though, is it possible to have the data imaged with a software, to see the distributed pressure that is?
Cheers!

[asurasnyx]

Hi

I don't know if this is something you can help with, but i'm looking to modify a chair so when it is sat on music/stories/sounds are played through something like an ipod shuffle do you have any idea how i would go about it, i assume somehow linking a pressure sensor to an ipod would work? but i don't know how to do it!!

Many thanks

[RobertY29]

I think it might be hard to queue the ipod BUT if you just let the ipod run you could get a cheap headphone extension. If you cut the extension in half you can kindof pull apart the wires inside it. If you strip off some of the insulation and then connect them loosely you can see which one turns off the headphones when disconnected. Wire that one through the switch. Then put the extension in line between the ipod and your speakers and put the switch wherever you want and you are good to go.

[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: https://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:
>> https://www.instructables.com/id/Conductive-Thread-Pressure-Sensor/
>> https://www.instructables.com/id/Pressure-Sensor-Matrix/
>> https://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:
>> https://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!

[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