DIY 21 LED Hula Hoop
Updated : FEB 28, See my website for more pictures and wiring diagrams.
21 led's inside a 3/4 inch pipe for faster hooping styles.
I previously made a instructable how to make a 42 LED hula hoop. But my most popular hoop on my site is the 21 LED so i decided to make another instructable for this one. It is very similar with a little different wiring.

Background:
I started learning about this because my GF wanted a LED hula hoop for christmas. After seeing sites online selling them for $250+ for rechargeable ones.. I decided i could make it myself for half that and rechargeable.

Takes about 3 hours to make

Step 1: Supplies

Here is a list of supplies you will need. All my prices are in Canadian funds. You can get things a little cheaper from ebay and such. But this was all bought from local
plumbing and electronics stores.

The hardest thing to find is a good tubing product. I wanted to use something that was fairly cheap, came in short lengths and had the proper strength and transparency i needed. The product i found that works best is Aqua-pex. It has writing on it with the brand and specs.. but it won't be noticeable at night , when you will be using a LED hula hoop anyway.

Supplies List
21 LEDS - $12.00 on ebay
132" of 3/4" pipe - $20.00 for 20 ft. Aquapex also available on ebay
1 x 3/4" pex coupler - $1.00 home depot or ebay
2 x 3/4" pex clamps - $0.50 home depot or ebay
36' x 22 ga Wire - $15.00 for 100 ft.
4 x AA NIMH rechargeable batteries - $18.00
1 x 6 volt battery charger - $15.00
1 x 1.75 x 4.75mm plug and dc Jack - $4.50
21 resistors - $2.00 for 100
1 x Slide Switch SPST on-off $$9.00 for 10
Everything comes to around $70
Plus a few basic tools you may already have.
Tools List
Soldering Iron, Drill, Solder, file or sandpaper, Flux, Electrical tape, marker, glue, pipe cutter, String, Wire strippers, Bubble wrap, and a paper clip.
http://farm4.static.flickr.com/3086/3184154764_7029162aae_t.jpg

Step 2: LED and Resistor Information

Resistors are basically used to drop the voltage so you don't fry the LED or draw more power then it needs.
Each LED requires a different voltage to light up. Some 2.4volts, some 3.6volts and so on.
Using OHM's Law, i calculated that with 4.8 Volts (4 x AA Rechargeable's). I needed 68 ohm resistors for the 3.6 V led's and 150 ohm resistors for the 2.4 and under
LED's.
Some people use exactly 3.6 volts, lithium or 3 AA batteries. But as soon as the batteries start dieing, they lose voltage and some LED's won't light up as bright or at all.

Use this tool to calculate which resistors you need for your LED's LED Resistor CalculatorLED Resistor Calculator
Soldering the resistor is very easy. You can put the resistor on either the negative or the positive. It doesn't matter. I used the positive. Usually on a LED, the positive is
the longer of the 2 leads. I cut my positive leads before soldering, to make the length of each almost the same after i solder the resistor.

Step 3: Soldering Batteries

So I started the process by soldering all my batteries together in series. Basically negative terminal goes to the positive on the next battery. I wanted to evenly distribute
the weight around the hoop so I separated the batteries by 31-36" of wire, so i had some extra to play with. I created a little video to show you how easy soldering a
battery is. . WARNING! Soldering batteries is very dangerous and they could explode. Try at your own risk.
Video
Soldering Batteries.
Prepping the batteries. I have used many different kinds of batteries. This time i am using Venom 2400 mah batteries. I start off by charging them. Then I take my cheap
nail file and scratch up the tops and bottoms. Just so the solder has something to grab onto.
Since my hoop is 132 inches, batteries are 2 inches long and i need 4 of them. I need to have etleast 31 of wire in between each battery. So i made it 32 inches just to be safe.
Strip each end of the wire.
Put some FLUX on the battery end and the end of the wire. It acts as a bonding agent for the solder and makes soldering so much easier.Put a big glob of solder on
the soldering iron. Touch your wire to the battery and push the soldering iron on top. It shouldn't need to be help on there for more than 5 seconds. Remove the iron, and
blow on the solder. It should harden and you will be able to pick the battery up with just the wire. If it falls off try again.

Step 4: Charger Plug

I changed the plug for the battery charger to a barrel plug. And used a hold jack for the receiver in the hoop. So the Jack could be more inside the hoop and less exposed. So I soldered the positive wire to the
middle and negative to the outer. It will be the same for the jack hole.

Step 5: LED Wires

I purchased 1 spool of Red 22 awg wire. So to distinguish the positive from the negative i took a marker and ran it down one length of the Red wire. I also purchased a second spool of white. You can use it for the second strand of LED's in the 42 LED version or use it for the batteries or what have you. I have recenlty switched to using white for both, as it is less visible through the hoop. And using only a piece of red at the end of the batteies line so i know when i pull the lines through the hoop which is the battery positive.
Next run the wires for the LEDS, Positive and ground. Mark out where you want the LED's and the batteries to go.
For 21 LED's per length of 132" wire. It was about 6.5 inches in between each led.
Make sure you leave enough room between the LED's for the batteries, no soldering or tape or they wont fit in the pipe.
Solder your resistors to your longer part of the LEDs.
And then solder the resistor to the positive wire.
Solder the other line of the led to the ground.
Tape up your exposed wires. And tape the wires together. Move on to the next led.
Always test the string before you move on to the next step. You can use a 9 volt battery to make it easier. Just touch the positive string to the small port and the negative
to the pole with the folds.
This step take the most time. Took me about 1 1/2 hour to do the 21 L.E.D.'s
Update:
I recently found out that you can attach the battery negative to the LED negatives. See the pic. This way you only need to attach the negative to the DC jack. And you don't have any wires going across the gap in the tubing when you are finished. Its works better this way for the collapsible version.

Step 6: Bubble Wrap Wires

After you are done soldering, you want to attach all the wires together.The led lines, the battery line and some string.
After all the lines are attached together. You want to bubble wrap between the batteries. To make the hoop quieter. And protect the led's.
Remember you want the batteries to be able to slide through the pipe. So only bubble wrap the led's and wires. leave that batteries exposed. Start at the end that will enter the hoop last. So the overlapping doesnt bind in the hoop when pulled through.
If you want to add some weight for a fitness hoop, just add some fishing lead weights in this step. Or make your hoop last longer using another 4 batteries in series. Double the Capacity.. but that would be a little more planning and different wiring.

Step 7: Charger Jack and Switch Placement

Next I drilled the holes for the switch and the dc jack. You want to place them far enough back that you can still get the coupler all the way in. I used a 1/4" drill bit. 1 hole
for the dc jack, 2 holes for the switch and just ran the drill back and forth till it made one long hole for the switch to fit.
In the pic i used a spare section of pipe just to test the placement.

Step 8: Pull the Wires Through

I attached another piece of string to the string tied to the lines, in the bubble wrap. At the end of that string i attached a battery for weight and slid it trough the pipe. I pull my wires through with the closed end of the wiring first.
Now with the wires sticking out the end of the pipe with the holes for the switch and jack. Take the positive LED wire and snake it through the Switch hole.
Take the negative from the LED/battery and pull it through the DC jack hole
I take the positive battery wire and pull it through the opening of the pipe. Then from there i snake 2 lines back one for the dc jack and one for the switch. Here is a diagram. and some pics Hope it makes some sense.

Step 9: Finishing and Connecting the Hoop

After connecting and soldering all the wires. I put glue/epoxy around the outside of the switch and DC Jack. Then pushed them into the pipe.
Now they should work while the hoop is separated.

Permanent:
Since I didn't want to buy the $200 tool needed for the pex clamps. You can just take your finished hoop to home depot and they will let you use their rental tool for free. Pex clamps hold great, and they are .28 cents each. Or you can use a gear clamp. Taped it up for aesthetics and safety.

Collapsible:
Now i use 3/4 x 8-32 screw posts and some 5/8 Round wood dowling in the middle of the tubing. Works great.