Image from ATX DIY
Adapted from http://www.atxdiy.com/2010/07/05/tutorial-sew-a-simple-circuit/
Sew-On Snaps- Make sure they are metal and not coated with paint, they need to conduct electricity. Magnetic snaps would also work
Needle – Needs to have a relatively small head
Conductive Thread –thinner is better
Strip of Felt – or any sewable, non-conductive material or fabric—felt is easy because you don’t have to hem!
LED – 10 mm work
Surface Mount Battery Holder
CR2032 Lithium 3Volt Battery
Permanent marker – Preferably a colored one.
Lighter – Optional, for burning ends of thread, I suppose a match would also work.
Round Nose Pliers
Scissors – for clipping thread
The main thing is to make sure your stitches are nice and even, tightly pulled, and not tangled.
1. CHECK THE LED: Identify the positive lead (the little wires that look like legs on the LED are the leads) – it’s the longer of the two wires. Now find the positive side of the battery (it should be labeled with a +). Place the LED over the battery so that the positive lead is touching the positive side of the battery, and the negative lead is touching the negative side of the battery. The LED should light up – if not, your battery might be dead, your LED might be bad (not very likely), or you’re doing it wrong (make sure the leads are only touching the corresponding side of the battery and not accidentally touching the opposite side).
2. Mark the long leg (the positive side) with a permanent marker. Bend the legs of the LED using the pliers into little mustache curly-cues using the needle nose pliers.
3. Cut about 36 inches of conductive thread off. Double thread your needle with a length (about 36 inches) of conductive thread and tie a knot at the end using both ends of the thread.
4. Measure your wrist using the felt. Mark where you would want the snap to go with a marker - the marks should be on opposite sides of the felt.
5. Place your LED in the middle of the felt cuff (on the top side) and begin sewing it on working only with the positive lead (the one you marked). Loop up through the circle a number of times being careful to pull your thread tightly in order to create a good connection between the LED and the conductive thread. Make sure you’re sewing tight and not getting too tangled—the conductive thread tangles easily. Pull tight carefully, checking that it’s not caught on anything!
6. Once you’ve stitched around the positive side of the LED, begin stitching out towards the end of the felt. Use a simple straight stitch. Sew until you get about 1 inch away from where you want the snap to go, and point your stitches downwards.
7. Flip the bracelet over and put your needle through. Start stitching through the hole in the battery holder closest to the positive side. Stitch up and down through the hole and the felt until it’s secure (you’ll probably only be able to pass the needle through two or three times as the hole is very small). Again, make sure that your stitches are tight and that the thread makes good contact with the metal tab on the battery holder.
8. Tie a secure knot in the thread and clip your thread leaving a tiny tail. You’ve just connected the positive side of the LED to the positive side of the battery holder!
9. SEWING THE NEGATIVE SIDE OF THE BATTERY HOLDER TO THE SNAP: Tie a knot at the end of your thread (or thread and knot a new length of conductive thread if you have less than a foot left).
10. Stitch the other side (negative) of the battery holder to the felt. Just like before, make sure your stitches are making good connections with the metal tab and you’ll probably only be able to get your needle through the hole a few times.
11. Once the negative side of battery holder is securely stitched, stitch a few stitches out to the end of the felt. This is where you’ll sew in one side of the snap.
12. Take one side of the snap (I used the pointy side that pops into the hole side) and stitch it to the felt. The snap will act at the switch for your circuit – when it is connected, electricity will pass through both sides of the snap and make the circuit complete. When the snap is disconnected, the circuit isn’t complete and electricity can’t flow through all the components. Like always, make sure to stitch the snap in carefully, creating a tight connection between the thread and the metal snap. Clip the end of the thread, leaving a short tail.
13. SEWING THE NEGATIVE LEAD TO THE OTHER SNAP: Thread a new length of conductive thread, making a knot in the end. Go back to the middle of your cuff – now you’ll be sewing the negative side of the LED out to the other end of your cuff.
14. Stitch up through the negative circle on the LED (remember, that’s the one that is not marked) and loop up and down through the felt and the LED legs a few times.
15. Now, stitch out to the other end of your cuff. Stop when you’ve reached the point where the other snap should go so that your cuff will fit your wrist.
16. Begin stitching the other side of the snap to the cuff – Make sure you are stitching it to the front (LED side) of the cuff.
Stitch the snap in securely and clip your thread.
17. Now you can snap the battery into the holder. The battery is labeled – one side with a + the other with a – . In the SparkFun battery holders, the + side of the battery needs to face up. Slide the battery in and push it in place.
When the snaps on your cuff are connected, the LED should light up.
If not - check the following things:
Is your battery dead?
Is your battery installed correctly in the holder (+ side facing up)?
Are all of your connections good (sometimes you have to jiggle things a little)?
Is your snap conductive and well connected?
Is the positive leg of the LED sewn to the positive side of the battery holder?
Is the negative side of the LED sewn to a snap that, when connected, is sewn to the negative side of the battery holder?
Make sure there aren’t any crossed or disconnected threads.