LED Array Help

I need some help with setting up an LED array. It has 440 or 480 lLEDs, I can't remember which, that operate at 2 volts and 35 mA. I want them in 11 or 12 rows of 40. How would I go about soldering them, what power source should I use, what resistance should I use, and is there a way to easily charlieplex that many LEDs? Thank you.

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tech-king9 years ago
heres the deal. if you wire a row in series, you need the micro-controller to give 80 volts. if you wire them in parallel, you need 0.035x40, or 1.4 amps. a bit more reasonable, but still more than a micro-controller can give. the solution: npn switching transistors. the base is attached to the ic pin. when the pin goes on, the base is powered and on. current can then flow from the collector to the emitter. when the ic stops powering the base, the transistor is off. you wire the bar of leds in parallel, attaching them to the emitter of their transistor.
so on your shopping list is:
  • micro-controller
  • 14 switching transistors with a amperage rating of 2 amps
  • 2 volt 2 amp regulated power supply. you may need to build one
  • a multimeter, if you dont have one. there will be a tarzan mess of cables.
  • zip ties, for the same reason
(cough, darlington pair, cough)
its better to connect the leds to higher voltage 'outside' of the regulated supply transistors can control higher voltage as wellas higher current
Ora (author)  tech-king9 years ago
Any chance you could give me a rough wiring diagram/schematic, even with much fewer LEDs, I don't really understand what you mean. How would I light up each LED separately?
110100101108 years ago
maybe you wanna do it fully digital numbered (instead of multiplexing) ? (treat the LED array like a memory structure) advantages : - less 'hell of circuit' more 'lots of identical modules conneced in parallel to the same 12 wires' - if LED is on - it really runs all the time and does not have to 'flicker fast'. speed of the circuit can be lower and LEDs work at true full brightness - requires 10 wires only (+ earth and 5V supply) to control up to 512 LEDs disadvantages : - requires lots of more components - the extra components have to be spread all over the construction together with the LEDs. may be undesired if construction is 3D or intended to be transparent
sandlehat8 years ago
Hey, working on the exact same thing here so i had to ask. Are you trying to replicate Thomas Bangalter's helmet from Daft Punk aswell?
westfw9 years ago
If you want to individually control the LEDs, then yes you'll need at least 22 pins (for charlieplexing) or up to 51 pins for a (much simpler) traditional multiplexing arrangement. Since you're well beyond "small number of pins", I'd seriously consider some sort of normal multiplexing arrangement using external IO expansion. You can check in the Arduino forums, where a lot of people are doing things with external "LED controller" chips. (Like this 8x8 NON-MULTIPLEXED module from http://moderndevice.com/8X8display.shtml Modern Devices])
In the traditional multiplex form, you'd be lighting up to 12 or 40 LEDs at once, and would need a suitable power supply (40 LEDs at 20mA each is about 1A,
so it's not THAT big a deal. You may want higher current since the LEDs will be OFF 11/12 of the time.)

Wiring that many LEDs will be a pain in the neck no matter how you do it. Can you use a couple of Evil Mad Scientist "Peggy" boards? They're set up to allow charlieplexing. On the other hand, a nice advantage of using traditional multiplexing is that you could build up your array out of commonly available dot-matrix modules.
(2x8 of 7x5 displays, for example: 16 rows of 40.)
Ora (author)  westfw9 years ago
I don't know about the arduino, I don't know how it could power 440 LEDs. The pegboard unfortunately doesn't work for what I am doing. I would like to be able to control any one LED at any given time. The array will be 11 or 12 rows of 40 red 3 mm LEDs. I just need to know how to wire them up, and what I need to wire them up to.
westfw Ora9 years ago
The point is that there are circuits that will go in between a microcontroller and an LED array that will "expand" the number of outputs available from the micro. For instance, you can cascade any number of 74xx595 (serial-in parallel-out shift register) on three or four microcontroller pins, and there are also special-purpose LED driver chips. Whether you use an arduino or not, these have been discussed quite a lot on the arduino forums. As for how to wire the LEDs up, let's assume a simple multiplex setup. So you get a piece of or something, and you drill 480 holes in it spaced appropriately, and of a size suitable for physically mounting the LEDs. 12 rows of 40 LEDs. Stick the LEDs in, with their leads all arranged to go the same direction, and glue them in with some sort of glue. Now, in each row of 40 LEDs, use a big long wire to connect ALL the cathodes of ALL the LEDs in that row. Repeat for all 12 rows: 480 solder joints. Connect the 12 wires to a couple of 74xx595s, or perhaps a higher-current version of the 595, or transistors driven by 595s, or even transistors driven directly by output pins from your micro. These are your "row drivers." Now, using shorter wires, connect all the anodes of all the LEDs in each COLUMN together (40 columns, 480 more solder joints, 40 resulting signals.) These get connected to column drivers (5x of 74xx595, as an example), probably through resistors. To light a single LED, arrange for the column driver of that LED to be at +v, and the row driver for that LED to be at GND. If you light one LED at a time, you can be very relaxed about power and drive capability. In theory, you can output +V on any number of the column drivers, but then the row driver has to be able to handle the sum of the individual currents to ground. (or, you can drive one full column at a time, which puts your current requirements at an intermediate level.) If you're capable of making your own single-sided PCB, then I'd change the wiring instructions a bit (but you'd have to drill 960 holds for the LED leads.) If you're capable of making your own double-sided PCB, or paying to have one made, things would change yet again.
Ora (author) 9 years ago
I figure if I'm going to charlieplex them, according to the equation n*(n-1) where n is the number of pins required to drive the circuit, I need 22 pins. Does that mean I need a 24 pin micro controller? This is going to be one hell of a circuit diagram...
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