200 LED project.

Hello Arduino World,

This is the first time posting in this forum and I'm excited to be a part of it. I haven't yet received my Arduino yet, but it's been shipped and should be here pretty soon.

On to the project. I'm interested in making an LED sign. I made one last year for my school; Marshall University. It was 20x30 and had around 200 LEDS. It was a huge hit, but after a rainy/snowy ride on a parade float it was destroyed. I want to come back bigger and better.

I want the same basic size of 20x30 for the back board and there are going to be around ~35 LEDS in each letter(six of them). Each letter should be ~8.5x11. I don't have any software that I can create a schematic, but I think I should be able to describe it pretty well.

20x30 backboard
6-8.5x11 letters "GO HERD"
~35 LEDS per letter

I want to be able to make the "G" "O" and "HERD" able to be lit up individually and on a PWM. Will I need transistors to use the PWM to controll the much larger array of LEDs? if so what should I look for when planning? For my last sign I wired them up in parallel with 1 led and 1 resistor each and then ran that to a momentary switch and then the positive of a 9 volt.This was bulky and heavy so I want to go thinner. Is there anyway to make or buy a board to make the sign a little slimmer?

Alright well that's enough info for now. Thanks for all the help guys. When this is done you'll be able to see it on ESPN when they air my schools football games!

Arduino pins can supply a maximum of about 40mA, LEDs typically draw 15-20mA, so more than two LEDs in parallel will require a transistor. If you use a 9V power supply, you can wire at least two LEDs in series which will halve the number of current limiting resistors you'll need and making the whole arrangement vastly more efficient. The number of parallel LEDs will determine the total current that each transistor will need to supply. What color are the LEDs you'll be using?

For the board itself, do you mean 20x30 inches? For that size and as simple as your design is, you could use a sheet of masonite (more durable) or foamcore (lighter) or gatorboard (like industrial foamcore, in between the two for weight/durability), drill holes for your LEDs to poke through and wire it all up on the back. Glue some spacer strips around the edges and a few blocks in the middle, and then you can attach another piece of board on the back to protect the wiring. A couple coats of Polycrylic or similar all over will help to weatherproof it.

You could drill holes in foamcore as suggested above, and if your leds are bright enough compared to the ambient light, you might even get a cool diffusion effect out of it, but my first thought would just be to poke the leads through the board so that the body of the led sits on the surface. I would probably then solder the leads to copper tape run along the back of the board.

Though a lot of people seem to be against the idea, I find that if you are using identical leds (mixing colors, brands etc. would be a problem), using a single resistor for several parallel LEDs works quite well, especially when they are grouped into clusters of a fixed quantity that all turn on/off together, as would seem to be the case with your project, so you may be able to get away with as few as one resistor per letter.

For transistors, MOSFETs would probably work, but I hope someone with more experience with such things will have a more confident and well-informed recommendation.

Also, if you want to try doing a schematic, the free version of Eagle will work, you just won't be able to use it to do the board layout (at least not at full-scale).

There will be trouble for Arduino to drive so many LEDS.
Check out this product, it fits you more.

The Arduino can easily run any number of LED's with just a few extra components. it's been done a thousand times before.

Wow this is such a great board. Fast and helpful replies. Thanks a lot!

Like a lot of you suggested I would be poking the LED's Threw the foam board. I have full page stickers that I will print letters and stick them to the foam board and then poke holes threw that so that on or off you will be able to read "GO HERD". My first sign was almost identical to what ajb suggested, but with some slightly different materials.

I'm going to use these green LEDs. http://cgi.ebay.com/200-pcs-5mm-Green-LED-Lamp-15000mcd-Free-Resistors_W0QQitemZ160349533833QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item255593b689&_trksid=p3286.c0.m14&_trkparms=65%3A15|66%3A2|39%3A1|293%3A1|294%3A50

Specs.
3.5V ideal
20 mA

The current is exactly why I was thinking about using the transistors. The arduino would no way be able to handle it on its own. So If I use the series way of wiring them what would my transistors specs need to be? Will the transistors be able to switch fast enough for the full fade effect of a pwm circuit?

Thanks alot

What does this "peak for 10% Pulse Width" mean? You can run them at 50mA only if you have the duty cycle at 10%?

P.S. I found the eagle program last night and am still getting used to it. I will try to whip up a rough schematic tonight. Thanks for the recommendation!

"What does this "peak for 10% Pulse Width" mean? You can run them at 50mA only if you have the duty cycle at 10%?"
Yes, 10% pulse and very short time.

20mA is the best work current.

Albert

Sure Arduino will do the job with few components ,but products like Rainbowduino makes the project easier.

If you are doing it in a matrix, you can just power rows and columns by using pwm to power the rows and columns. Then in theory you only have to be powering 1 LED at once, and you can do massive displays with limited pins. Look at this link:

http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1235795499/0#0

for an alternative to the other boards as you already have an arduino. I am doing a similar project with linking a lot of 8x8 led matrices together (but not for showing sport stuff).

Mowcius

Wow, well I really tried with Eagle. Please bear with me this is my first drawing. Any suggestions and criticism are greatly appreciated! I'm not quite sure I wired the transistors up right. Anyway here it is...

keep in mind the sets of 1 or 2 leds will represent the ~35 LEDs in each letter.

a parallel version(after posting this I realized that I didn't connect the "D" to the ground) sorry!!!


a series version

I'm really leaning toward the parallel version because I'm worried about the charge being distributed threw the LEDs evenly.

Yeah sorry I missed the bit about lighting up using templates for the letters. I presumed that you wanted to be able to scroll the messages etc. and show other stuff but if you only want to show specific letters then I would have thought that an arduino is a bit overkill... You could use something as simple as a 555 timer chip to flash the letters.

Lighting up 35 LEDs in series is a seriously bad idea and doing it in parallel will no-doubt kill your chip because there will be too much current going through it.

Mowcius

I want a bit more functionality than a 555 timer. Like the ability to write some different patterns and flash sequences. I will not be running them all in series. Only 2 per series, but the 2 seriess' of Leds will add up to ~35 per letter. Besides I'm leaning away from that all together and doing them in parallel. Also, I will not be using the arduino to run them all directly. That is what the transistor is for. The arduino will tell the transistor when to turn on and that will allow charge to flow threw the Leds.

You'll need some nice big transistors...

Mowcius

If you are using two separate power supplies for the Arduino and the LEDs as your schematics indicate you will need to join the negatives together so that there is a common reference when you supply power to the transistors. Otherwise it won’t work.

Why would you not wire the LEDs in series pairs? If you wire them entirely in parallel, that’s 200 * 20mA = 4000mA consumption at full bore. If you run them from 9V, that’s 36W total, of which 22W is going straight to heat through the current limiting resistors.

On the other hand, wiring them as series pairs, they’ll only consume 100 * 20mA = 2000mA, totaling 18W, of which only 4W will be dissipated by the current limiting resistors. Efficiency will be massively improved and your battery life will be doubled.

Oh sorry, I did not get the 'series pairs' bit, I presumed, for some reason, that the 35 LEDs were going to be put in series together...

Mowcius

For something of this scale, perhaps look into the M5451

Runs 35 LED's with a single resistor for brightness control. Also holds state of each LED so there is no need for POV tricks.

That is what the CCShield (ConstantCurrentShield) has. It has 2 M5451s to drive 70 LED outputs. Then you can use pwm (pov tricks) to drive more LEDs in a matrix if necessary...

Mowcius

ajb,

Thanks for all your help on this. You've convinced me to run them series to be more efficient. It's only logical and it will make for a better product. One final question about that though; does running Leds in series make them more prone to dying? I want this to last as long as possible so that I don't have to keep putting in new Leds after every game.

I'm not really too sure of how to use or integrate a M5451 chip as I'm pretty new to this. Is there any reason a transistor won't work for now?Furthermore is it expensive?

I received my arduino last night and spent the better part of the day(after working of course lol) learning the language. Some of the basics are kind of tricky, but I managed to write 3 of the patters that I was looking for. They are rather basic, but still something I had in mind. Tonight I will fix the drawing of the schematic and make sure it's right from you guys.

This is right? both of the grounds are touching eachother.

Thanks for all your help on this. You've convinced me to run them series to be more efficient. It's only logical and it will make for a better product. One final question about that though; does running Leds in series make them more prone to dying? I want this to last as long as possible so that I don't have to keep putting in new Leds after every game.

The LEDs should last 50000 hours depending on conditions...

I'm not really too sure of how to use or integrate a M5451 chip as I'm pretty new to this. Is there any reason a transistor won't work for now?Furthermore is it expensive?

Transistors will work fine for you... But you won't get fading from the transistor so you might as well use a 555 timer chip to control it instead of an arduino...

The M5451 chip is ideal for controlling lots of LEDs individually so you could have an LED matrix and scroll messages etc on it. They are not that expensive...

I received my arduino last night and spent the better part of the day(after working of course lol) learning the language. Some of the basics are kind of tricky, but I managed to write 3 of the patters that I was looking for. They are rather basic, but still something I had in mind. Tonight I will fix the drawing of the schematic and make sure it's right from you guys.

Yeah it can be tricky starting off... (Some of us are on holiday - or maybe it's just me!)

Mowcius