Wednesday, March 20, 2013

[DIY] Conductive Fabric Electrodes

Released under CC BY-NC-SA 3.0
Conductive fabric electrodes are a low cost and simple way to make reusable electrodes for sensing muscle activity. They can be sown into any type of garment or used with a strap. When dampened, these electrodes allow you to sense the tiny electrical signals of your muscles just like traditional medical electrodes. For this tutorial, we're going to use them in a sleeve to detect the muscle activity of the forearm muscles.

Benefits of the conductive fabric electrodes over traditional EMG electrodes:
  • Reusable - traditional EMG electrodes are meant to be used only once and then thrown out. Conductive fabric electrodes can be used over and over again simply by applying some water before use.
  • No adhesive - traditional EMG electrodes use adhesives to stick to your skin. This adhesive can be some what of a pain to remove after use and can cause skin irritation to some people.

Benefits of the traditional EMG electrodes over conductive fabric electrodes:
  • Ready to use - you can simply buy these electrodes off the shelf and use them right away.
  • Can be placed on any muscle - conductive fabric electrodes are sown into garments making so they can only be used by the intended muscle group the garment is matched with. Traditional electrodes can be simply place on any muscle group you might want to use as the trigger muscle.

Materials


Step 1 - Preparing the Conductive Fabric Strips


To make a conductive fabric electrode sleeve, we'll need to make three contact points above the muscle we want to sense. In this case, we're after the forearm muscles.
  1. Cut out three rectangular strips of the conductive fabric. Two of the strips should be W 5/8" x L 1 3/4". The third strip should be W 5/8" x L 2".
  2. Take the forearm sleeve, turn it inside out, and put it on the opposite arm that it is intended to go on.
  3. Using fabric pins, pin the two shorter strips on your forearm muscle such that one is in the middle of the muscle body and the other is about an inch apart. Pin the third strip along the back side of your forearm (on the bony part). Check out the pictures to see how to orient the strips.
  4. Carefully take the sleeve off and you're ready to start sowing.


Step 2 - Sewing the Conductive Strips


Since the sleeve is very stretchy, we'll need to use a stitch that will give us the kind of flexibility we need and also keep the conductive fabric in place. 

Luckily, we've got the zigzag stitch. The zigzag stitch is basically an overcast stitch in both directions. Use a zigzag stitch to sew each of the conductive fabric strips to the sleeve.

Note: Since you'll be wetting these strips before each use, you can also use a waterproof backing (like neoprene fabric or thin rubber) to help keep the moisture in one place. If you use backing, use the zigzag stitch to first attach the conductive fabric strips to the backing material strips, then use the zigzag stitch to sew the backing to the sleeve.


Step 3 - Adding the Electrode Cable Snaps

By this point, we have the conductive fabric strips securely sewn into the sleeve, but we still need a way to attach the electrode cables to the sleeve.
  1. Using the button snap kit, attach a male snap to each of the conductive fabric strips. Make sure the male side is on the outer side of the sleeve as shown in the picture. The snaps can be placed any where along the strips but should be placed where the three cable lead ends can easily reach it.
  2. After the snaps have been attached, use a multimeter to test the connection between each snap and its conductive fabric strip. To do this, simply place on probe against the conductive fabric strip and the other probe on the snap.

If each connection is in working order, then you're finished! 

18 comments:

  1. Can you specify the fabric that you have used? Thanks

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    1. Hi, you can find the list of materials just above step 1 in the Materials section. Click on the links to go to a vendor that sells them.

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    2. I was curious about this as well. They offer several types of conductive fabric for different purposes. Basically I was looking at the Copper, Nickle/Copper, and Silver fabric. They say the Nickle/Copper may produce skin allergies so better to got with other two. I'm guessing the Riptop Silver is the best choice since it's a better conductor.

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    3. Use the "Stretch conductive fabric". I've updated the link to navigate you straight to it instead of the top of their product page.

      http://www.lessemf.com/fabric.html#321

      "This medical grade Silver plated 76% Nylon, 24% elastic fiber fabric offers the unique ability to stretch in both directions. Can be used as an antibacterial wound dressing (note: our material is not sterile) but it also makes a great material for electrode contacts, stretchy hats, socks, gloves, or other garments. Highly conductive, and conductivity increases as it stretches in one direction, and decreases as it stretches in the other direction. Silver coating is 99.9% pure. Silver/gray color. "

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    4. Thanks! Do you know what size snap buttons are needed?

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  2. So this is to measure how much of a workout you are getting?

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    1. That is one application but the sensor is not necessarily limited to it. You can use it to control computers, robots, etc as well as monitor muscle use and strength. Check out our tutorials for other applications.

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  3. Can you measure the individual finger-pulling muscles in the forearm separately, in order to make pentambic keyer armbands? I've wanted to do this for years. Make it Bluetooth so you can enter text into any computer or phone just by moving your fingers in chording patterns while holding arms in a neutral posture, without touching anything or wearing gloves.

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  4. That's interesting! You give the size of the strips in the tutorial, is this the minimum size or can you make it smaller? How do you choose the size of the strips? I was thinking about putting more than one EMG channel in such a sleeve

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  5. What size snaps?

    Or better yet, what snap kit did you use?

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  6. What type of snaps do you need? What size?

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  7. I was wondering... do those snaps don't get polarized after a while? I mean, that's why electrodes generally consider some kind of special material (Ag/AgCl or Platinum)in order to reduce that effect.

    Are these snaps different to common clothing snaps?

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  8. Dexter, you are correct , they will polarize and become less effective as normal snaps are nickle coated brass which can also be a problem if you are allergic to nickle. Best option is still adhesive electrodes.

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  9. It's interesting that you matter-of-factly mention wetting the conductive cloth, but in my recent test adding just a bit of moisture for conductivity isn't a trivial addition, it's a *major* influence for the better, although too much and it's no-go. I still need to find a sweet spot as I just finished these preliminary tests, but it seems clear that an addition to this post on the importance of conductivitity-enhancing wetting would be worth mentioning. Like: how much, just water or perhaps some better alternatives, and how long the wetted material is expected to remain functional. That would be awesome. Otherwise fantastic post, thanks!
    ps : what does Dexter mean on the snaps getting polarized? Does that mean that prolonged use will eventually get affected in some way?

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  10. Is there a way to also detect when bending your elbow?

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    Replies
    1. Yeah, just use a flex sensor. https://www.sparkfun.com/products/8606

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  11. Hello, we feed the plate with two 9V batteries getting voltages of +9 and -9, the output I have a variation of 0-5 volts or 0-9 volts ?? sorry my english is because the translator, I'm from Brazil thank

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    1. If you use +/-9V the max output of the sensor is +9V. If you use +/-5V, the max output will be +5V.

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