Instructables
A guide to creating illuminated shapes with balloons and LEDs.  Although this instructable demonstrates how to create a red-illuminated balloon heart, these techniques can be used to create most any shape (possibly 3-dimensional) of your own design.   The actual assembly of this example took approximately 2 hours to complete.
 
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Step 1: Materials

Picture of Materials
The materials needed for this project include:

-20  latex balloons
-20  LEDs
-20 3v coin cell batteries
-Sticky-notes
-Tape

I used red LEDs and pink balloons, but any colours will do.

Step 2: Assembling the LEDs

The balloons are illuminated by LED-throwies which are documented in several variations on instrutables.  Here is how I made my Led throwies. 

First trim down the anode ( + long lead) and cathode ( - short lead)  so that  the length of either lead is shorter than the diameter of the battery.

After the leads have been trimmed down, wrap a strip of paper around the cathode lead of the LED. 
Then, insert the battery between the leads of the LED with the strip of paper.  I used scotch tape to hold everything together, but most any tape will do.



Step 3: Assembling the balloons

Picture of Assembling the balloons
I did not have a tank of helium to fill the balloons myself, so I went to a local grocery store and ordered 20 pink latex balloons.  I asked if they would mind putting throwies into the balloons before inflating and they were willing to help.   So, I left them with the 20 pre-assembled throwies in a bag labeled with instructions to pull the pink slip of paper out to illuminate the LEDs.  An hour later I pick up my balloons and was ready for assembly.

I doubled over strips of tape t stick the balloons together side by side.  The reason I had popped a balloon was  that I pulled the tape on the balloon and the latex ripped.  As a precaution I also tied the balloon strings together as a stress relief for the taped areas.

killbox3 years ago
I just did a instructable about flying LED's i called Flyies.

one thing to watch out about the led's is most have a very sharp little lip at the base of the led, (its in how the plastic is cast) so your tape should go up past the base of the led, to avoid balloons from popping if shaken/blown by the wind.

you can also find CR1025's cheaply and they will light a led for about 4 days. they will also just slip into a balloon without much struggle. My first ones used cr2032's and had to fill the balloons to near bursting to fly here (1 mile above sea level) that night out of 20 of them only one did not pop. sue to that sharp little bit on the led. and the way it lies on the bottom of the balloon.