8x8 dimmable matrix array with ~3W LED's - pilot project - research for now

[eatkabab]

I'd like to create a dimmable LED matrix that's Arduino controlled using some variation of an XLamp (XPG, XRE, XML...).
I've never even made a simple array, but I feel I can learn/manage the limited basic programming part. The complicated part is that most arrays run on low voltage and even lower current (~80ma absolute max I could find)...how do I get it powerful enough to drive a ~3W LED?

My first idea was to put a dimmer driver on each LED then have them all tied into a breadboard....way too many wires and too expensive for all those drivers. There's gotta be an easier way to do it. Traditional matrix arrays are just a grid of wires with an LED at each point and control the X, Y. Can even get simpler if PWM is used to control the entire array from half the lines... My goal is to have the final product be home lighting...

Any input or direction of where to look is greatly appreciated



Sorry this thread was supposed to be in "general lighting"

 

[RoGuE_StreaK]

Maybe investigate the Texas Instrument chips like the TLC5926 or the TLC5940? Controllable constant current sinks, can tie together multiple sinks per LED to increase current.

 

[nickelflipper]

I'd like to create a dimmable LED matrix that's Arduino controlled using some variation of an XLamp (XPG, XRE, XML...).
I've never even made a simple array, but I feel I can learn/manage the limited basic programming part. The complicated part is that most arrays run on low voltage and even lower current (~80ma absolute max I could find)...how do I get it powerful enough to drive a ~3W LED?

My first idea was to put a dimmer driver on each LED then have them all tied into a breadboard....way too many wires and too expensive for all those drivers. There's gotta be an easier way to do it. Traditional matrix arrays are just a grid of wires with an LED at each point and control the X, Y. Can even get simpler if PWM is used to control the entire array from half the lines... My goal is to have the final product be home lighting...

Any input or direction of where to look is greatly appreciated



Sorry this thread was supposed to be in "general lighting"

You want individual led PWM? If so, I don't see how it gets done for less than $3-4 a pixel.

 

[evilc66]

Easiest way to do this is to treat it like a smaller, low current array. Just use transistors/FETs with a current limiting resistor on each LED, and treat the FET as you would the low power LED. You would have the high current wiring run in parallel to each FET/LED combo, then the low current signal to each FET. Should keep the wiring to a minimum, and the controller will be guarded from over-current.

 

[eatkabab]

You want individual led PWM? If so, I don't see how it gets done for less than $3-4 a pixel.

Even $5/pixel would be good if that included the driver and wiring...

 

[eatkabab]

Easiest way to do this is to treat it like a smaller, low current array. Just use transistors/FETs with a current limiting resistor on each LED, and treat the FET as you would the low power LED. You would have the high current wiring run in parallel to each FET/LED combo, then the low current signal to each FET. Should keep the wiring to a minimum, and the controller will be guarded from over-current.

I was thinking of that as well, but it won't give me the intensity modulation I seek...

 

[eatkabab]

Maybe investigate the Texas Instrument chips like the TLC5926 or the TLC5940? Controllable constant current sinks, can tie together multiple sinks per LED to increase current.

Good option, but only 120ma max. I'm looking for at least 500ma max stable. Maybe I can run a few in parallel? That might be getting too complicated/hackish...

 

[Norm]

Sorry this thread was supposed to be in "general lighting"

It was originally posted in General Flashlight Discussion. Is there some where else you would prefer it to be? - Norm

 

[nickelflipper]

Even $5/pixel would be good if that included the driver and wiring...

I'm an optimist :) .
Forgot about needing a 200W+ power suppy, adjustable voltage would be nice too.

The tlc5940 (or similar) is the answer to PWM linear drivers like the AMC7135 or your FET's. Cascade four tlc5940's to get 64 PWM thru SPI from the Arduino. Or you could use just about any other PWM shift register chip like an I2C version from NXP PCA9635PW for instance. You do need to source current to the AMC7135 Vdd pin, which doesn't need much, and shouldn't be a problem. I say this because most of these led driver chips come advertised or spec'd as sinking current.

The AMC7135 can be had as 350ma, 700ma, 1050ma slave led drivers (pcb mounted, no micro) that come individually, 20 packs, or even mounted on aluminum stars. Lots of shopping to be done.

 

[RoGuE_StreaK]

Good option, but only 120ma max. I'm looking for at least 500ma max stable. Maybe I can run a few in parallel? That might be getting too complicated/hackish...

As I said, just tie a few sinks together in parallel, it's designed that way. Two chips in parallel will (well, should, still haven't tested) give you 3840mA with 32 steps of adjustment purely by turning pins on and off, let alone any greyscale PWM with the 5920. If you tie four pins together you'll get 480mA, and four sets of these per chip.
It's designed to run in a daisy-chain, input of the first one gets sent out it's output onto the input of the next one... should be able to use SPI even though it's not really SPI per se.

[EDIT] got held up mid post. As per nickelflipper, you could also use a single sink of the 5940 to drive a 7135 or two, using the 5940 as the serial-to-parallel interface to your current sinks. That said, you can get freebies from TI, so just design a board with lots of 5940s in series

 

[eatkabab]

Excellent help!! Thank you very much. I personally don't like linear regulators so I'd prefer to stay away from them. I'll do a little more research on the TLC's. Thank you!

 

[DIWdiver]

Do you want to be able to turn on any random group of LEDs at one time? With the 'traditional array' of 8x8 wires and an LED at each crosspoint, you can only turn on one LED at a time, or certain groups of LEDs, but not any random selection.

You can make it appear to light any random group of LEDs by lighting any group in one row, then any group in the next row, etc. Each row is lit 1/8 of the time (aka 1/8 duty cycle). If you run through all 8 rows at least 100 times per second, you can't see the flicker (well most people can't). 200 Hz is faster than anyone can see, and quite possible for a microprocessor, though digital cameras and video cameras can pick it up.

This approach has some major advantages:
- One 5940 can control the entire matrix.
- Only 16 wires to the array
- Simple circuitry

It also has some serious disadvantages:
- Each LED is only on 1/8 of the time
- It's nearly impossible to use switching regulators, so efficiency is not good.
- You almost have to use resistor current limiting, one per LED.