Peggy: Like Lite-Brite with LEDs

Evil Mad Scientist has been really putting out the LED projects lately. They were selling a Mooninite kit, then they had pink LEDs (yum), and now they have info on how to make Peggy, an LED display where you simply plug them in and watch them glow. This 25 x 25 grid allows you to worry about what image you want to glow instead of how they're going to be wired up.

Evil Mad Scientist page

Picture of Peggy: Like Lite-Brite with LEDs
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phenoptix9 years ago
Stunning.
note: i have 0 experince with leds couldnt you just use rgb leds and have a controler that would allow you to change amounts of r g b and switch to controll different led?
fredricksburgthethird: It's a lot more complicated than you might guess.

Going from driving the 625 LEDs (easy) to driving 625 LEDs fully individually controlled takes some work. But controlling 625 RGB LEDs means really controlling 1875 r, g, and b LEDs individually. Maybe that's not so bad if you're driving each LED as either "on" or "off" but you really want each LED element to be intensity controlled as well, with at least 8 bits of resolution. So, you really need a set of external drivers that can control the intensity of every single one of those 1875 chips. Minor details....

I'm certainly not afraid of building one like that *except* that it gets expensive fast. If you had an array like that, you'd certainly want to fill it up. Right now 10 mm RGB diffused LEDs cost about $0.40, so we're looking at $250 in LEDs alone on one of these. The driver hardware would also be more expensive, so this gets to be more like a $300-$400 project, not a $100 project.
Kiteman9 years ago
I like that - can you pop the LEDs in and out on a whim (in which case I like it a lot), or do you have to solder them in?
oskay Kiteman9 years ago
They're soldered in. (Adding 1250 sockets gets expensive and takes a long, long time.) You can put LEDs in and light them up and move them around *before* soldering. ;)

Seriously, though, it might be fun to try using mechanically weak conductive glue to attach the LEDs-- then you could pull the LEDs out with a little bit of force and reconfigure it easily. Do you know of any types that might work?
Magnetic Fridge Lights! would resolve the socket issue - BUT, that comes at a cost of requiring each LED to be custom made (magnet and such) and appears to have a lower "resolution". It also adds a resistor on each LED (that needs it - but this probably isn't as robust as your board)....

Nice work though :)
westfw oskay9 years ago
You know, you don't really need a socket for every possible position right away. For the first effort, you solder in the sockets for the LEDs used by your first picture; it takes about the same amount of time as soldering in the LEDs (plus the time to install the LEDs into the sockets.) Poof; done. Now your project sits around for a few months, or years, and you decide it's time for a new picture. So you pull the LEDs out of the sockets, figure out where they'll go next, and solder sockets into just those places that don't already have sockets; again, this isn't much more difficult than creating a new board. Repeat as needed, buying more sockets as necessary; eventually the whole matrix will have sockets, and each picture will only take a maximum of the number of LEDs in THAT picture. What you need is a cheap ugly socket that can mount on the backside of the board, probably using an extra set of pads, so the LED legs can go through the normal mounting holes and into the socket. No ideas there :-(
I think I might buy this and solder on the 1250 sockets. I know it would take forever, but it would be well worth it! :D Buying the sockets wouldn't be a problem, because I have a friend that can get stuff for me for free! (I might have to get down on my knees and beg for more than one thousand though) I know he could get them for me really cheap if the begging doesn't work.
Kiteman oskay9 years ago
What about conductive silly putty? You could mix in carbon granules or fibres, then use it like blu tac.
One word: Magnets
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