Trippy Filter: Costume for Burningman

March 10, 2005 12:16 PM

I've got an idea for a costume for Burningman, but I'm going to need a bit of electrical help to figure it out. I want to use A set of LED's like these connected to cheap hobby quality fiber optic cable ala This sort of chintzy stuff.

The Idea is this, the LEDs cycle quickly between red, green, and blue to produce white light. However due to persistance of vision, as I move, it looks as each point of light is producing a rainbow type effect. I'd like to use these LEDs as light source for some cheap hobbyist fiber optic cable( I know where to get this stuff online quite inexpensively) and then route the fiber optic cable along my costume to produce hundreds of little points of rainbow light. I'd also like to get a big clear plastic tube and put a bunch of these lights at the top and use it as an illuminated walking stick. Clearly I need some powerful LEDs.

I've found that over-the-counter type battery operated LED systems like the one I linked to are not only expesive, but dim, last only a few hours, are difficult to attach a more long lasting power supply to, and have expensive batteries to boot.

Ideally, I'd like to make the LED system myself primarily because it would be cheaper and brighter. I'm fairly handy with a soldering iron, but I don't really know alot about electronics, specifically, the details of powering LEDs and the circutry necessary to make them cycle fairly quickly so that the red green and blue LEDs appear to be white when they are stationary.

What I'm looking for is a good reference to teahc myself the basics that i need to know in order to hack together something that will work, as well as a cheap place to order parts.

I'm also open to buying a kit, or a complete product that will fit my needs, as long as it is relatively cheap and bright.

I'm willing to spend a few hundred dollars on this project.

Thanks for your help.

posted by Freen to technology (16 comments total)

You might want to ask this guy.

/got nothin'
posted by furtive at 12:50 PM on March 10, 2005

This modding site has an example, although they use only one rainbow LED. They say the speed is adjustable.

This costume sounds like it'll be bulky to say the least: you will need a battery pack, a place to "hide" the escaping light of the LEDs (what the cables [or thin plastic] don't pick up), and the wires will have to point out somehow at the audience (Look at the picture that you give as an example- where are the cables the brightest?). It sounds like the stick alone might be more realistic.
posted by Monday at 1:00 PM on March 10, 2005

Lots to answer.
First point - different colours of LED operate at different voltages - from 1.8 to 4.8V (and there is some voltage variation between LEDs of the same colour). This is no problem - you power them all off the same voltage) but put the appropriate resistor on each LED. (They need resistors anyway). There is a formula for working out the resistor, but there are plenty of resistor calculators online these days. Cheap 1/4W resistors are ideal.

For a wealth of info about LEDs, check out LED Museum

I recommend 4.5V as your power supply. Ie three AA cells, or any similar combination (eg two banks of 3 AA cells in parallel, or 3 C cells, etc). This is a safe voltage for HC and CMOS chips, and it will drive your LEDs at full brightness. (LEDs that need 4.8V for max effect are uncommon)

For really bright LEDs at low prices, I recommend www.superbrightleds.com.
Another option is Electronics Goldmine.
For resistors, Mouser is a trade/warehouse type retailer that sells to hobbiests. Individually, resistors are 9c each (compared to 40c at radioshack), but if you're going to buy more than four, you might as well spend $1.80 and get a pack of 200 - less than a cent each.

For colour cycling, I use the HC4017 decade counter chip. This is pretty simple to use - run it off 5V, and there are ten output pins that it cycles from one to the next each time you put power into the clock pin. You can connect LEDs directly to each output pin and ground, and they will cycle, but to drive more than one LED at any one time, you will need to put a transistor on each pin instead and have the transistor drive the LEDs as the current from the HC4017 pins is 25mA (from memory), and you want something closer to 30mA. (or greater if you're prepared to go beyond what the LEDs are rated for). There is also a reset pin. Connect this to the forth output pin, thus it will cycle through pins 1-3, and reset back to one on the next step.
To drive the clock pin at a high speed, you will need to connect it to an oscillator circuit - these are simple and cheap and schematics abound on the net.

Discover circuits is a mother lode of circuits and projects online.

As to an introduction/understanding of (almost) the kind of electronics project you're looking at, I recommend this book. It's about making simple toys and robots from broken junk, but is an interesting guide that strikes a good balance between showing you how to actually get your circuits working in the real world with limited tools, and teaching you the electronics involved. It's not the kind of "basic electronics" book that is almost purely maths and physics. Those aren't fun :-)
posted by -harlequin- at 1:04 PM on March 10, 2005

Furtive: Nope, That's electroluminescent wire, or EL wire. That's what I used for last year's costume. I'm going to use a bit of it for my bike, and probably a couple of sound senstive red heart that beats in time to the music. But yeah, he'd go over well at burningman too.

Monday: Awesome. Thanks. LEDs don't use much power, and i was planning on having a "utility belt" type power supply, with the appropriate electronics inside that plug into a connector on my jacket and pants. There would be individual LEDs or a groups of LEDs, depending on the power that connect directly to fiberoptic cable inside the jacket, and along the outside of the belt, that connect to the fiber optic cable. I was thinking about using electrical tape as a light shield. The wires don't necessarily have to point at the audience because the light is out of phase, it will disperse once it hits the end of the fiber optic cable.

-harlequin-: thanks. I'll check that stuff out.
posted by Freen at 1:16 PM on March 10, 2005

-harlequin-: It looks as if this is the LED I'm looking for.

It looks as if it uses 3.5v and 2v all at 20mA.

I think I'd like to set up an array of 4 or 5 of these for each light source. Could I use the same oscillator and decade counter chip to power such an array or multiple sets of LEDs.

i.e. One power source, with one chunk of electronics, and wires going out to the different light sources, probably three of them, each with 4-5 LEDs.
posted by Freen at 1:36 PM on March 10, 2005

Yes, one power source, one chunk of electronics (including transistors on the decade counter outputs), and your average transistor (such as BC548) can be good for 500mA, meaning you could connect a bank of 25 LEDs off that transistor simultaniously. (If you need more, add another transistor to the output pin, note also that transistors should be connected to the pin via a resistor, forgot to mention that, I'd think somewhere in the 10K to 48K range)

To do it properly, you want a resistor on each LED (or 3 resistors per RGB LED), but you can get away with just using one resistor between transistor and its LED bank. Doing this is not recommended because natural variance in semiconductors means that one LED will have lower resistance than the others, and will therefore soak more current, running hot, and possibly damage itself. But in this case, it's probably worthwhile, since LEDs are pretty hardy and you'll be doing a lot of soldering otherwise :)
Just remember that if they're all being driven from the same resistor, it needs to be a hardier resistor, not a 1/4 Watt one. (eg 500mA x 4V = 2 Watts, so you'd need a 2W (or bigger) resistor, though it sounds like you're thinking of smaller LED banks than the transistor's maximum, eg five LEDs at 20mA is 100mA x 4V = 0.4W, so a 1/2W resistor would be called for.)

Also, I'm not sure what you mean by using 4 or 5 for each light source - do you mean glue them together into a larger, brighter lump, and attach the fibres to that? If so, a potentially better approach would be to buy single-colour LEDs and amalgamate those instead of RGB ones, as the single colour ones come in much brighter versions (probably up to ten times brighter). You'd have to play with resistors (or better - potentiometers) to find out what the right R-G-B balance was to get a white, but you might have to do that anyway - I wouldn't know whether or not the RGB leds produce white when all colours are on full. It would be nice if they did, but wouldn't surprise me if they're not pre-balanced.
posted by -harlequin- at 2:05 PM on March 10, 2005

Yep they do actually produce white when all colors are on full, that's why i think they would be ideal.

Yes, i'd like to glue a bunch of them together to produce a brighter light, or perhaps have a row of them so that they could rest in my pocket or line the bottom on the jacket instead of being one giant clump of LEDs.
posted by Freen at 2:13 PM on March 10, 2005

Also, any suggestions for an oscillator circuit? I'deally I'd like something that goes at about 24hz, perhaps less, or that can be tuned to anything from 1hz to 100hz so that I can play around to find the best speed.

Are there kits i can buy, or would it be best to just get a crystal and do it myself?
posted by Freen at 2:29 PM on March 10, 2005

Maybe use a 555 timer chip?
posted by Freen at 2:50 PM on March 10, 2005

Scroll down to "suspended bicore", more info here. It's a simple oscillator that uses 4 components (2 caps, a resistor, and an HC04 chip). Changing the caps or resistor affects the speed, so if you use a potentiometer instead of a resistor, you just turn the knob until it's oscillating at the desired speed. Try 0.1uF caps and a 100K pot. (To get 1hz, you'll want a 1M pot, but if you want to be able to fine-tune the rate, you'll want either a pot with a smaller range (eg 100K) or a multi-turn pot. Trimpots range from a few cents to a few dollars, so you might as well buy 1M, 100K, 10K and 1K and experiment. I also highly recommend a solderless breadboard. Never even touch a soldering iron until your circuit works on the solderless breadboard.
posted by -harlequin- at 2:53 PM on March 10, 2005

Actually, you might need 5M for 1hz, not sure. Experiment and find out. The higher the resistance, the slower the oscillations. Same with the capacitance of the caps.
posted by -harlequin- at 2:55 PM on March 10, 2005

Cool. I think i'm going to try both methods and see what works best. I'm looking for about 12-48hz, as below 12, the Persistance of vision breaks down, and above 48, you really wouldn't see the flicker unless it was moving quite quickly.

I'm definitely not going to solder until i get the thing working.
posted by Freen at 3:08 PM on March 10, 2005

But then again, maybe i want it to be tree times as fast, because there are three lights to cycle through, so maybe something like 32hz-144hz.
posted by Freen at 3:19 PM on March 10, 2005

Anyway, Thank you so much for your help, -harlequin- I'll let you know how the project goes.
posted by Freen at 3:20 PM on March 10, 2005

For the most powerful LEDs, look at Lumiled's Luxeon series. Their Blue Star III can sink 3 Watts and serves as a substitute for a laser in a lab I work in. Their white versions can power computer LCD projectors.

The 555 timer chip mentioned above is certainly a good start, though you'll need to buffer the output with a power transistor if you're thinking about driving lots of current (maybe more than 100 mA or so). Feel free to email any specific electronics difficulties.
posted by fatllama at 11:48 PM on March 10, 2005

Damn, those do look bright. I think i may use em for a flashlight, or maybe a floodlight for the camp while i'm there. The thing that is nice about the other LEDs is that they are color balanced to make them white when they are all on at full power, and they have all three primary colors in one LED. It looks as if it's going to be a new moon, so pitch black at night on the playa.
posted by Freen at 8:08 AM on March 11, 2005