Introduction: Auto On/Off LED Throwie

Picture of Auto On/Off LED Throwie

This is my version of the LED Throwie. The design isn't mine, this is just my mod of it. In the original design, the LED Throwie is on from the moment you put it together. This can be annoying if you're planning to make tons of these, or if you want to make them ahead of time but not have the battery run out. Someone has already posted a mod that adds an on/off tab to the throwie, however I've taken it one step further: in this design the throwie automatically turns on when it sticks to something, and turns off as soon as you remove it! It's just as simple to make as normal throwies, and doesn't require any extra materials either! These also work great as simple LED pinch lights. Credit goes to everythingdigital for the idea (it was mentioned in a comment), but the implementation is mine.

I'll point out that though this instructable may seem long or complicated at first, it's only because I wanted to make sure it was well documented. It is actually VERY easy and VERY quick to do. Making these throwies should be just as easy, and take no longer than the original design. Once you've done one and you understand how it works, you'll be whipping these out in no time.

From the original throwie:
Developed by the Graffiti Research Lab a division of the Eyebeam R&D OpenLab, LED Throwies are an inexpensive way to add color to any ferromagnetic surface in your neighborhood. A Throwie consists of a lithium battery, a 10mm diffused LED and a rare-earth magnet taped together. Throw it up high and in quantity to impress your friends and city officials.

Step 1: Parts and Materials

Picture of Parts and Materials

If you only intend to make a few of these, or just want to try them out, you can get all the parts you need at Radioshack. However if you plan to make a large quantity, you should buy all your parts in bulk online, as Radioshack would get kinda pricey for more than a few of these. You can go to the original throwie article (https://www.instructables.com/id/LED-Throwies) for info on where to buy the parts.

What You Need:
-5mm Diffused LED (the original uses 10mm, but these were cheap in an assorted pack at Radioshack, so I got them)
-CR2032 3V Button Cell
-3/8" x 1/16" Neodymium Disc Magnet
-Scotch Tape, or Strapping Tape (Strapping is better, but Scotch works fine)
-Double sided tape, or just about any glue
-Leftover cardboard from battery package/other packaging

Note: The magnets I used were 3/16" diameter (that's all Radioshack had at the time). They seem plenty strong for just sticking the throwie to things, however if you wanted to actually throw it at something, I think you'd want something a little stronger so that it would actually stick. I'd recommend 3/8" diameter by 1/16" thick, though you can try other sizes and see what works best. What is important is the magnet has to be smaller than the battery - half the size should work fine, two-thirds is too large. You'll see what I mean when you see how the design works.

As of March 2011, if you purchase all the parts at Radioshack, one throwie would cost you about $7 ($5.50 of that is the battery). 
According to the original throwie article, if you purchase all your items bulk online, you can get the cost down to about a doller per throwie.

Step 2: Bend the LED Wire

Picture of Bend the LED Wire

The first step is to bend the LED's wire. You want it so that the space between the two wires is just barely wider than the width of the battery plus the magnet.

To start, test the LED by placing it so one wire touches each side of the battery. The longer wire typically goes to the positive side (top) of the battery, but as some LED's are different, if yours isn't working just flip it and try again. 

Next you want to make your first bend. The wire to be bent will be the negative side. Using needle nosed pliers, make a perpendicular bend a little over 1/8" below the LED (see picture).

Now you need to bend the wire back to parallel with the other. Determine where to make the bend by placing your magnet on your battery and comparing to their width. Your next bend should put the spacing between the wires just barely thicker (think about one wire's width) than the battery and the magnet. Look at the images to see what the bend should look like.

Step 3: Make Your Separator Platform

Picture of Make Your Separator Platform

The next step is to make a platform that will hold the LED wire away from the magnet.

To make this more clear I will describe how the final assembly will go together: the magnet will sit on the negative (bottom) side of the battery, pushed most of the way to one side. Directly opposite it will go a platform that prevents the LED's negative wire from contacting the magnet. There will be about 1/8" between the magnet and the platform. The LED wires will slip over the battery, magnet, and platform from the side of the magnet. The positive wire will simply touch the entire positive side. The negative wire will go all the way over the magnet, and sit on the platform, suspended just barely over the magnet, close but not touching. When the throwie sticks to something, the wire will be pressed into the magnet, completing the circuit. See the pictures for a better idea.

Cut a strip of cardboard from the packaging the battery came in, about 1" long to start, and about 3/8" wide.
Fold the cardboard back and forth, until you have a piece of cardboard about the thickness of the magnet (3 layers for me). Using double sided tape or glue, stick all the back and forth folds together to make one piece. Put a piece of double sided tape on the bottom of the platform to stick it to the battery.

Once the piece is glued or taped, it should be just thick enough to sit on the battery next to the magnet, and hold the LED wire less than a wire thickness above the magnet.

Note: if the LED is lighting up, before you assume your platform is too thin, try applying pressure to the very end of the negative wire, so as to lift the middle part off the magnet. This is usually all that is needed to make it work, and your platform is most likely the right size. When you perform the final wrap of tape around the assembly, the tape will apply this pressure so that the circuit remains broken.

Look at the image to understand more clearly.

Step 4: Wrap the Assembly

Picture of Wrap the Assembly

The final step is to wrap the entire assembly in tape. You can use either strapping tape or scotch tape for this. Strapping tape is more durable, but scotch tape worked fine for me.

Take about 2" of tape, and wrap it around the entire assembly. Pull it tightly over the end of the negative wire, until the middle of the wire no longer makes contact with the magnet and the LED stays off.
If the LED is not going off, try repositioning the magnet, or making the platform slightly thicker by adding a layer of tape. Also the space between the wires could be too little, so try adjusting the bend so that there is enough space for the wire to hang over the magnet without touching it. It may seem tricky at first, but after you get it once you'll get all of them correct right away from then on, without any adjusting needed.

That's it! Make a bunch, and go out and have a throwie party! Throw them at anything magnetic, and they should turn on as soon as they stick! Also useful as a pinch-on LED flashlight!

Disclaimer: The original design is not mine; this is just my modification of it. I take no responsibility for what you do with these.

Comments

kavya10 (author)2015-09-05

send a video of it

LeithG (author)2015-07-05

Thanks for the design revision it will be usefull, i did a price up yesterday (4th july 2015) I priced it in at about 40 cents australian to make a throwie
But thay was buying the 3v batteries from aliexpess at 21USd for 250 of them, 600 5mm LED (100 RED 100BLUE 100 GREEN 100PINK 100 YELLOW 100PURPLE) 20 AUD and 200 magnets for 20aud so excluding the wastage which i will just use for other projects total was 75 aud for 200 throwies (plus tape so at best 80) so its come down a fair bit now in price to make these bad boys if you buy online.

Wee Heavy (author)2013-03-09

Could this version be made without the magnet!

vborkar (author)2011-05-25

DUDE WHOEVER U R U R JST TOOOOOOOOOOOO GOOOOOOOODDD
COZ THE NORMAL LED THROWIES REMAINS ON SO THE BATTERY DRAINS FASTER U R THE BESY GUY IN HTE WORLD!!!!!!!!!!!!!!!!!!!!!
U JUST ROCK

fkhalsa (author)vborkar2011-05-25

Haha, thanks dude!
I'll try and get some better pics up soon.

ppanchal1 (author)fkhalsa2012-06-15

THESE PICS R GOOD
U ROCKX

no_light (author)2012-04-12

you can use electrical tape rite? or like duct tape?

mg9990 (author)2012-01-04

do you know how long they last when they are on with the battery you are using? This is a really brilliant idea because I always thought it was dumb that throwies never turn off :/

lhong4 (author)2011-11-06

Does the magnet stick onto the battery by itself? if it could, I am thinking of just taping one of the legs to the battery then leave the other hanging slightly above. When I am ready to light it up, I just need to push the hanging leg down with the magnet. I don't plan to really throw it around so there's no worry of having the magnet coming apart midair.

freakyqwerty (author)2011-08-28

You should defiently use the macro setting on you camera, it's the flower icon...

fkhalsa (author)freakyqwerty2011-08-28

As I noted in another comment, the only camera available to me at the time was my iPhone 3G, which does not have a macro setting (or else I would have used it).

I plan to retake all the images for this instructable soon, using a much nicer camera, that is capable of macro photography.

Thanks for commenting though!

freakyqwerty (author)fkhalsa2011-10-15

Good 'ible anyway :P

fnawaz (author)2011-05-20

good,,,,,,,,,,,,,,,,,,,,,,,,,

fkhalsa (author)fnawaz2011-05-25

Thanks!

ForgerOfPie (author)fkhalsa2011-08-06

You know somebody loves your project if they congratulate in all CAPS.

Excellent instructable from an excellent user. Great job.

fkhalsa (author)ForgerOfPie2011-08-06

Thanks a lot!

gumbylove (author)2011-07-25

Ikea sells a pack of 8 CV2032 batteries for .99 cents. Way cheaper than the $6 brand name pack of 2.

ForgerOfPie (author)gumbylove2011-08-06

It's Ikea! What else would you expect? :)

fkhalsa (author)gumbylove2011-07-26

Cool, thanks!
I found some cheap ones online, on Amazon.com and eBay as well.

zazenergy (author)2011-03-07

Looks cool! Any chance you can include clearer photos?

fkhalsa (author)zazenergy2011-03-07

Thanks!
Sorry about that, all I've got right now is my iPhone 3G, but as soon as I get access to a better camera I'll put in better pics. Hope they're at least usable.

About This Instructable

54,553views

83favorites

License:

More by fkhalsa:Auto On/Off LED Throwie
Add instructable to: