# leds.

hello everyone. i just started using my arduino and actually programming and doing circuitry 2 days ago. im learning slowing its alot of fun. i was just wondering how many leds can the arduino control. i have a huge idea that if i can figure out id like to do over the summer.

There are ways to make Arduino control a large number of LED's

Search the forum for charliplexing, multiplexing and led matrix that should give you some good starting points.

Usually theese methods need some extra circutry, and an external powersupply.

basickly i want to make a small bill board out of a piece of ply wood 4' x4". im not sure how many leds ill need but i know its going to be alot. thanks for the help.

Wow, sounds like a cool project. One of the first things you will need to pin down is how many LEDs.

Lets say you decide on 1 LED per square inch. That is 144 * 16 = 2304 LEDs!!! This is an ambitious project.

To start with, you should familerize youself with Peggy2 from EvilMadScience. And its color derivative ClockTHREE. When you understand that circuit, you can scale up from there.

Justin

That is 144 * 16 = 2304 LEDs!!!!

It's also a significant number of Watts.

Oops, I see now that you said 4 feet x 4 inches: 48x4 square inches = 192 square inches. Much easier to manage. Peggy2 handles 625 leds, so that architecture has got you covered.

"It's also a significant number of Watts." Not necessarily - if they are arranged in combinations that would allow many to be in strings running from 1 voltage source, say 100V DC, then one could have 50 LEDs in each string (say to form a single segment of 7-segment display for example), then there would be 46 strings at 20mA each (with typical LEDs and not some high wattage LEDs for example), so 9-10 amps of current. Times 100V - I guess even like that would be 900-1000W. Still, no worse than a few light bulbs.

4' x 4" = 48" x 4" = 192 square inches. Looks a unit check is in order to start with. 4 feet x 4 inches, or 4 feet x 4 feet?

http://www.mpja.com/prodinfo.asp?number=18460+OP 4" high x 3" wide, 16 of these would fill a 48" board, 560 LEDs. String of shift register like 74AC299 down the length of the board. P-channel MOSFET to source current for the rows. This particular part is common anode vs common cathode, could be driven like this:

Find a P-channel logic level MOSFET that can source 500mA, if find a higher drive part than have it drive more columns.

Heres a board I am busy finishing off with 2528 LEDs ( they are red, interestingly, as in the reflection on the right, not orange as the camera sees full power )

http://www.flickr.com/photos/johnandlyn/5526322956/

If all the LEDs were on ( which cannot happen with the text characters ) it would only draw 12.16 amps from the 12 volt 150 watt power supply I am using.

Some of the LED strings are 5 LEDs in series, and the alpha ones are 4 ( different resistors balance the brightness ) none are multiplexed, the LEDs columns are latched on with high power shift registers that cost 5 US cents each ( thats one of the reasons )

Damn! That's a lot of LEDs!

it would only draw 12.16 amps from the 12 volt 150 watt power supply

“only”?

But it would not be an overload , 12 * 12.16 = 145.92 watts,

But that would have to be with both teams drawn at 88 points/goals each at 88minutes and 88 seconds left on the clock :-) and I am not even going to try and work out what the names of the teams must be to get maximum LEDs on ! :P

Hey Crossroads, thankfully I have some retired people who are happy to solder LEDs all day !!! ( and they are not in prisons like China ! )

But it would not be an overload , 12 * 12.16 =

Oops - sorry, read it as 12.6A

But it would not be an overload , 12 * 12.16 = 145.92 watts,

Well drawing 145.92W from a 150W supply is what I would call an overload, it's just too close to the spec to be comfortable.

But it could never get near that, with both teams on the score of 88, and at 36 min and 36 seconds left in the game, the numbers would have 200 led strips on @ 18mA = 3.6A

and with team BBBBB playing against team BBBBB the letters would also have 200 strips on @ 18mA = 3.6A

so the max current in real life ( for one second while the teams are tying 88 each ) is 7.2 Amps.

Which is less than 58% of the 150 watts which is perfectly safe.