This cap Instructable is a part of our larger Lumenhattio project, in which we're experimenting with ways to make stretchable glowing helmet covers that provides affordable, changeable style by day and safety light by night. We recently presented the Lumenhattio at the World Maker Faire, and a lot of folks suggested that this is also a great project for teaching kids about electricity! The cap requires only 5 inexpensive materials to make, and because of its low voltage power supply and the resistance of the conductive thread, you won't get zapped with electricity while you make this cap!

Step 1: Materials

• 20 to 30 Piranha LEDs
with identical voltages (check part specs)
we tried: http://superbrightleds.com

• 20 feet of Conductive Thread
we tried: http://sparkfun.com

• 1 Spandex Cap
available at sporting or beauty supply stores
we tried: Feel Beauty Supply, Brooklyn

• 1 Sewable Coin Cell Holder
we tried: http://sparkfun.com

• 1 Coin Cell Battery
CR2032 220 mAh Lithium Ion
we tried: http://amazon.com

• 1 Mid-Sized Needle

Step 2: (Preliminary) Examine the LEDS

Study the piranha LED. Like all LEDs, the piranha LED is bipolar, with a positive (+ or anodal) side and a negative (- or cathodal) side. On a piranha LED, two leads are positive and two are negative. Often, one side is marked with holes or a missing corner, as in the photos below:

Step 3: (Preliminary) Examine the Battery

Study the cell battery. The positive side is marked with a "+" sign, while the negative side is usually unmarked.

Step 4: (Preliminary) Determine LED Polarity

Determine the polarity of your LED by holding the battery between the LED’s two poles. Each side of the battery should touch the two prongs of each pole. Once the LED lights up, you’ll know which side of the LED is positive and which side is negative.

Step 5: (Preliminary) Understand the Battery Holder

Add the battery holder into your setup. Put the battery into the battery holder and use conductive thread to connect the battery holder to the LED. When the LED is correctly connected to the battery holder, the LED will light up.
IMPORTANT: the thread connecting the positive poles must not touch the thread connecting the negative poles.

Step 6: Examine the Spandex Cap

Study the spandex cap. If this is your first time making this cap, it’s a good idea to stud the LEDs along the seams of the cap. Using the cap’s seams helps to isolate the positive side of the circuit from contact with the negative side of the circuit, thus preventing short circuiting.

Step 7: Plan the LED Layout

Design how the LEDs will be laid out on the cap. In the cap pictured below, we studded 25 LEDs along the center seam of the cap. We used white LEDs only and colored 13 of them red with a Sharpie.

(Most LEDs of different colors have different forward voltages, meaning that they cannot be connected in a parallel circuit without additional parts.)

Step 8: Stud the LEDs

Stud your LEDs on the cap according to the design you just planned. You will now see why piranha LEDs are used instead of standard 2-prong LEDs—the 4 prongs of the piranha LED provides better stability in attachment to the spandex.

Remember to push each prong all the way through the spandex as you stud your LEDs. There’s a little “crossguard” on each prong that makes it harder to get the prong through, but once the prong is all the way through, the crossguard will help the prong from slipping out.

Step 9: (Optional) Push Prongs Slightly

(Optional) If you're going to transport or move your project frequently, it may be helpful to push matching prongs slightly towards each other (positive to positive and negative to negative). This will help keep the LEDs slightly more securely in place. Do not push the prongs all the way down, because you will need to wrap conductive thread around them.

Step 10: Sew Positive Prongs

Sew conductive thread to connect all positive prongs together. As you sew, loop the thread around each prong, then press each prong down all the way to fully secure each LED in place.

Step 11: Sew Negative Prongs

Sew conductive thread to connect all negative prongs together. As you sew, loop the thread around each prong, then press each prong down all the way to fully secure each LED in place. Make sure that the negatively-connecting thread has NO CONTACT with the positively-connecting thread.

Step 12: Test the Battery Holder

Thread the positively-connected thread through the positive lead on the battery holder, then thread the negatively-connected thread through the negative lead on the battery holder. All your LEDS should now light up. If they do not, try reversing the threads’ connection to the battery holder. If the LEDS still do not light, check for and remove any contact between the positive and negative threads.

Step 13: Sew the Battery Holder

Sew the battery holder securely to the spandex cap. In the picture below, we used regular (non-conductive) thread to help keep reinforce the battery holder and to hold the positive and negative threads in place.

Step 14: Final Notes

As we've made more of these caps at The DuKode Studio, we've started to prefer the use of two needles so that the positive and negative line can be sewn simultaneously. If you add the battery while you are sewing with two needles, your LEDs will light up as you sew! This can be very useful to ensure that everything is working. As mentioned earlier, the low voltage of the power supply and the resistance of the thread make it so that the cap won't get hot or electrocute.

We would love to see of your finished caps, please send pictures to info@dukode.com. Have fun making and using this LED Glowing Helmet Cap!