Conductive Thread Pressure Sensor

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Introduction: Conductive Thread Pressure Sensor

About: My work combines conductive materials and craft techniques to develop new styles of building electronics that emphasize materiality and process. I create working prototypes to demonstrate the kinds of electr...
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.

Step 1: 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

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

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

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

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

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

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!

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    43 Comments

    I am looking for someone to help with small scale art installation fabrication integrating audio and fabric art. If you are interested please be in touch through Contact form on dreamline.blog

    hi there, I've SEM project coming soon.. so my project gonna be a math mechanical compases where it can draw while measuring the angle at once.. can I put a sensor on it?

    hi can we use to find pressure of pen grip by win ding it with the pen

    Greetings Plusea,

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

    Thanks in advance.

    1 reply

    Just to get a better idea of what you're trying to do, what exactly are you trying to do? Different pressure turns on different lights? What is your exact idea for a project?

    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!

    1 reply

    It definitely sounds possible, but not without a microcontroller like an arduino. This is a analog sensor and arduino had a ton of examples with similar sensors if you aren't too familiar with them.

    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?

    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?

    1 reply

    Hello Plusea

    Is that possible to measure big load in this system?

    Thanks

    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.

    1 reply

    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 :)

    2 replies

    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.

    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???

    1 reply

    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

    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!!

    1 reply

    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:
    >> https://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.