Ever wanted a durable and reliable soft circuit button? With just a little bit of conductive thread, two pieces of fabric and some batting you can make your very own.
The materials you'll need:
- 1/8 yard of non-conductive fabric
- 1/16 yard of non-conductive batting
- 36" of conductive thread
- 2 conductive snaps
- A little bit of velcro tape
- A piece of paper to draw a pattern with
- An Arduino circuit to test with
You can get most of these materials from any fabric or craft store. Batting comes in different weights depending on how fluffy you want it to be. You can also replace it with neoprene or felt, but that won't be as soft or as pliable.
And the tools:
- Sewing Machine
- Hand Sewing Needle
- Tailor's Chalk
- Quilters' Pins
To test out the soft circuit button, I made a quick circuit for my Arduino. The button can be attached to any of the digital pins to act as a simple on/off switch. When attached to an analog pin, it can even act as a rudimentary pressure sensor. Plus, if you have some anti-static foam (the stuff your electronics are usually packed with) you can stuff it inside your button and turn it into a DIY Force Sensitive Resistor!
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Step 1: Sewing on the Conductive Thread
Cut out three squares of paper of the same size. Take one of them and cut out a smaller square in the middle. Place the one with the hole in the middle on the batting. This is going to be the pattern you follow. Whenever sewing things together, you always want to leave a little bit of room on the fabric for seam allowance. So pin down the paper pattern on your batting then cut out outside the paper's edges, leaving about 5/8" of room on each side. Cut out the middle also with a little bit of seam allowance.
Take two pieces of fabric larger than the square patterns that you cut out. Sew diagonally across the fabric pieces on the bias. You may want to practice on a scrap piece first. Check the tension of your machine. A good trick for sewing with conductive thread in the bobbin is slightly lowering the tension of the top thread so the bobbin thread floats a little bit. This sometimes jams the machine, however, so be aware.
After sewing diagonally, sew a square pattern on one of the pieces and a cross-hair pattern on the other. You may want to draw it out with tailor's chalk beforehand to help guide you. Test the pieces with a multimeter to make sure the conductive thread connects to each other from end to end.
When you're finished sewing with conductive thread, line up the fabric pieces so the conductive thread is facing up. Make the diagonals face the same way. If you flip one over and place it on top of the other piece, it should create an X with the conductive threads. This will prevent short circuiting and make things easier later when we have to attach it to some wires for the circuit.
Step 2: Sewing Together the Button
Now comes the fun part! ... It's also a complicated part.
Take the piece of fabric with the conductive square pattern in the middle and place the batting on top of it, conductive side facing up. Line them up so the hole in the batting leaves the conductive pattern open. Pin the pieces together and sew them together with non-conductive thread.
Stack the two pieces of fabric with the top thread (non-conductive threads) facing each other. Align the cross-hair so it overlaps the square pattern. Sew three sides of the button together. Then cut about 5/8" away from the seam, leaving even less room around the corners. When finished, flip the button inside out so it forms a pillow with the batting in the middle.
You've now got a perfectly functioning conductive button. Don't believe me? Test it with a multimeter like I did in the video.
Step 3: Finishing the Button
The final edge I like to be able to open and close at whim for debugging and for upgrading. So I attached some velcro tape on the seams. Finally, you're going to want to attach this button to your Arduino or other soft circuit. I didn't want to permanently attach the button to jumper wires. So I sewed on some conductive snaps to the conductive threads instead, one on for each side of fabric. That way the wires can be snapped off when needed.
Always test your button with the multimeter first, in case it shorts. If all goes well, you can attach it to the Arduino Circuit I showed in the beginning of this instructable. Here's the code to light up your LED.
But wait, there's more! I mentioned this button can also be an FSR. Well, if you have some anti-static foam (the kind they often package electronic components in) you can place it inside your button and turn it into a pressure sensor. Neat, huh?
I hope you found this useful. Let me know what you think. Always open for suggestions!