Ask MetaFilter questions tagged with LEDs

How is this color-changing LED array being driven?

jjjjjjjijjjjjjj — Tue, 18 Nov 2008 12:18:24 -0800

Electronics/LED Folks: I bought a few cheap, poorly-assembled LED color-changing orb-things and I'm pretty sure they're the coolest objects I have ever owned. I cracked 'em open, and damned if I know what is going on in there, but it looks simple/cheap as all hell. Help me figure it out, I'll post a build-log/parts list somewhere, and in short-order we can all be ass-deep in home-made, disarmingly sublime mood-lighting. So it's about the size of a tennis-ball, made of hard, milky plastic, and it cycles in a smooth, slow gradient between Red, Green, and Blue. (8-Second Video: Globe On, Globe Off). That's it. It doesn't look like much, and it's no danger of "blowing anyone away" or anything, but lemme tell you... it has absolutely transfixed the dozen or so people that've been to my house in the week I've owned it. I'm talkin' young, gadget-savvy folks who absolutely should know better. But we all love the stupid little thing.

Cracked it open, and inside are three 1.5V watch batteries, 3 LEDs (one each: red, green, blue), a resistor, a switch, a board, and a tiny mysterious shiny black spot.

I'd like to know what method they're using to cycle thru these colors.

This schematic represents my closest attempt at understanding the build. I'm sure you'll agree that there is at least one key element missing. It is my (unfounded, but) strong suspicion that this missing element is a very simple one (though I am very interested in answers, simple or otherwise).

MORE PICTURES:
* LED board, top
* LED board, bottom
* Switch/Battery assembly

There's a huge chance that I've unknowingly left out something of dire importance. I will try to clarify/photograph anything that is needed. I have the disassembled globe on my workbench as we speak... multimeter at the ready.

Another related question: Would there be any way to run a common anode high-power RGB LED star off of a configuration similar to what is being used in the globe above? I'm interested, very generally, in novel methods that can be used to drive RGB (or separate "R, G, and B") LEDs. I'm slowly getting the hang of PWM and microcontroller/Arduino-based methods, and I like what I've learned... but I've not come across much that deals with any other methods. Thanks to all.

LIGHT SHOW

god particle — Mon, 26 May 2008 16:17:02 -0800

I'm interested in learning how to wire LEDs and program/control them. I want to learn how to wire a lot of LEDs together and then program or otherwise control them, so that I can trigger certain ones to go on or have them play in sync with music, or something of that sort. Preferably I'd like to be able to control the lights by hand through some sort of device/interface. I don't really know much, if anything, about electronics and programming. The most I can do is solder a couple LEDs to a battery and have them turn on. What resources should I turn to to get started?

Silly question about flashing...

twine42 — Wed, 06 Feb 2008 07:44:13 -0800

I have a question about persistence of vision and flashing lights... There will be maths and biology involved. Imagine you have two LEDs. They each produce one hypthetical unit of light (1 HUL if you will). If they're both turned on, they produce a combined 2HUL.

Now imagine that they flash at a rate greater than 25fps in a way that when one is on the other is off.

Ideally they are producing 1HUL. In reality the light up time probably means it's a little less than this. But here is my question:

What does the human eye *think* they are producing? Do you see the equivalent of 1HUL, 2HUL or somewhere in between? Does it matter if you are looking directly at the LEDs or at a surface being illuminated by them?

I've used 25 fps here since with cartoons a frame rate above 25 fps creates a moving image... it may be a red herring.

Need a place to purchase around 50 LEDs in San Francisco

agenais — Wed, 05 Dec 2007 11:46:04 -0800

I need to purchase 30 to 50 orange or red LEDs by this Friday. Where can I get them as cheaply as possible in/around San Francisco? I need these lights for a project that has to be completed by the end of this week. I've purchased this set of lights from eBay a few days ago, but I doubt they're getting here in time.

The lights should be orange or red. Diffused/wide angle LEDs preferred, but not necessary. Size isn't important, but around 10mm sounds good. Purchasing 50 lights from Radio Shack is pretty pricey. I considered cannabilizing a set of LED Christmas lights, but it might be a pain in the arse to extract each light individually.

Do I have any other cheaper options for getting these lights in San Francisco? Are there awesome electronic stores that sell them in bulk, or should I suck it up and hit up all the Radio Shacks in the city?

Where's my future-car?

limeonaire — Sat, 25 Nov 2006 13:54:43 -0800

It seems that taillights have evolved rather radically from their humble origins, now featuring LED configurations spanning cars' entire back ends. Why hasn't this kind of innovation been seen with headlights? I thought of a few questions along these lines last night while sitting in the back of a friend's van, watching the headlights around us on the highway.

Specifically:

1. Why don't car manufacturers use fluorescent or LED bulbs (backed by reflective material, just as incandescent bulbs are) in headlights? It seems to me that they'd be just as sturdy as incandescent bulbs, and probably provide brighter light with less energy required.

2. Are there practical reasons why car manufacturers continue to stick to the tried-and-true "two headlights, one on the left, one on the right" configuration, rather than using, say, a centrally mounted light bar? (Think something like the Millennium Falcon's propulsion bar, only on the front of the car and used solely for lighting purposes...) Or is it just convention?

When I discussed this with my friends, we speculated that it could be an issue of redundancy—i.e. if one gets knocked out, you still have one left. But then, I countered, couldn't that be addressed by mounting, say, two or more fluorescent tubes in the "light bar"? Or if fluorescent tubes are too fragile, perhaps multiple tiny white LEDs?

We also speculated that perhaps it was just a design/functionality issue, wherein, say, the grill is a standard air intake area for the engine, and it's easier to keep it there, rather than trying to create a radically new air intake system.

Any ideas which, if any, of these issues have curtailed the introduction of new forms of headlights?

How to build a massive LED array

bjork24 — Mon, 26 Jun 2006 11:02:03 -0800

Continuation from my last question: how do I make a giant red "M" out of little LEDs? After reading all the answers from my previous question, I became enamored with the idea of building the big red "M" out of LEDs. The only problem is, I know about as much about LEDs as I do needlework, which is to say, nothing at all.

Can someone point me in the direction of a tutorial that will help an absolute noob like me learn enough about LEDs to build the "M"? This is going to be a massive array of LEDs, so the "build your own LED flashlight" articles aren't really helping me.

Illuminated Shoes

Rash — Fri, 14 Oct 2005 10:36:10 -0800

Tell me about little kids' shoes, the ones with the flashing LEDs. What are they called? Is it just a specific brand?

It's curious that I never see 'em advertised -- guessing that's because I'm in the wrong (non-breeder) demographic.

And imagine my disappointment when I learned they're powered with batteries -- this nerd assumed they were piezoelectric, as a standard project in any Science Fair when I was growing up involved the light bulb, the crystal, and the hammer.