LED Pixel display - Page 1
Forum section: electronics / beginners

author: iampoor
author_rank: Frequent Contributor
timestamp: March 02, 2016, 07:32:24 am
content: HiI am currently interested in building some LED matrix's.I have seen many smaller examples using WS2811 based LED Tape, but I am looking to build a lower resolution much brighter panel. I am thinking of using 5-10w RGB LED's in a 16x8 matrix. I would like this to be controlled by DMX and am planning on using Lightjams or Glediator (Leaning towards lightjams right now, as many other lighting fixtures are supported).The planning part is easy, now comes the part I have no clue how to accomplish. What would be the simplest way to control these? I am assuming I will need to design my own constant current LED driver, unless a decent off the shelf solution exists. But the real part I am lost on is: What would be the easiest way to interface these with DMX?I have seen quite a few Led Pixel drivers that drive strings of WS2081 or LPD6083 based LED tape (IEhttp://www.j1sys.com/products/lighting/ECG-PIXAD8.html) , but no high power variants of these style constant current drivers. Maybe using WS2081's and then building an LED driver on top of them would be the easiest? I need these displays to be extremely bright, but am not sure where to even begin with as far as controlling them. If anyone could point me in the right direction, that would be much appreciated. This p[roject is still in the very early stages of development. Very excited to start learning.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 02, 2016, 07:54:04 am
content: DMX is easy - all you need is a UART - I'm sure there are multiple Arduino libraries out there.You'd need multiple PWM outputs to control the drivers (assuming you want intensity control) - something like a PCA9685, which gives 16 channels from I2C. If you just need on/off control it's even simpler.If low cost is the priority and you don't care about efficiency, you could get away with resistive current limiting and carefully controlled supply voltage, and a bunch of fan-cooled power resistors.What colour? If white will do , look at using off-the-shelf LED filament lamp replacements, e.g. MR16 types with internal drivers.

author: johm
author_rank: Contributor
timestamp: March 02, 2016, 12:36:33 pm
content: If your focus is only the LED Matrices, and you want to control them using for example Lightjams, I suggest you buy a USB to DMX module such as ENTTEChttps://www.enttec.com/?main_menu=Products&pn=70303or use the Arduino shieldhttp://playground.arduino.cc/DMX/DMXShieldalthough I don't think it will work on LJ.On the other side, take into account how much current scales up when driving LEDs, it is easy to get beyond 5A when dealing with long runs of LED strips or muxed matrices. So design with that in mind.

author: Divvi
author_rank: Contributor
timestamp: March 02, 2016, 04:49:45 pm
content: Quote from: johm on March 02, 2016, 12:36:33 pmIf he is planning on using 5-10 watt RGB leds similar toTHESE, he has bigger issues than just long runs:400mA / color * 3 * 16 * 8 = 153.6 Amps @ ~ 3V = ~460Watts for White at full brightness. That's going to generate quite a bit of heat. More for the 10w LEDsQuoteYep, possibly. You will need a micro to process the DMX UART and output the SPI required for the WS2081's.

author: iampoor
author_rank: Frequent Contributor
timestamp: March 04, 2016, 09:34:53 am
content: Quote from: mikeselectricstuff on March 02, 2016, 07:54:04 amYes there are quite a few libraries. However, I have realized that the software I am planning on using (and the number of pixels I need) will be better suited by using ArtNET or aSCN. ArtNET to dmx nodes are still pretty pricy, so I wonder if it might be better to build something using off the shelf mappable pixel ICs.Actually, using this as a main controller looks promising too with its aSCN Input, 4 aSCN to dmx outputs, then I could build another finer resolution LED wall with its insane number of pixel outputs.Then I could build a DMX interface with the arduino on each LED matrix. This seems to be the most affordable and expandable option!http://www.advateklights.com/shop/mantis-pixel-mapping/16-pixlite-16-controller.htmlQuoteYes, definitly need intensity.Thanks, I have been reading the datasheet for the PCA9685. Looks really nice and pretty easy to use!QuoteCost doesnt have to be that low thankfully! I found a driver IC that looks pretty decent and affordable. A whole reel of 500 is under 30$ on alibabaOrdered 10, we will see how they work.http://www.electroschematics.com/wp-content/uploads/2014/07/PT4115E-datasheet.pdfSince I am using RGB LED's, I am thinking of build a board with 24 LED drivers each, and having 1 per row.QuoteI am looking at using RGB Led's like thesehttp://www.ebay.com/itm/RGB-LED-Light-Bulb-Beads-10W-Lamp-Bulb-1pc-High-Power-Super-Bright-Integrated-/400423640521?hash=item5d3b1bddc9:g:qFkAAOSw5dNWlKT~Unless you have a better suggestion. I ordered a few samples and have found they are not particularly consistent....would like to find a reputable supplier!Quote from: johm on March 02, 2016, 12:36:33 pmThanks. I have used the entec interface before. Pretty nice, but I need more channelsYes, current consumption will be pretty high. Thankfully these run at 12vQuote from: Divvi on March 02, 2016, 04:49:45 pmYes, heat is one of the large unknowns as of now. They will be in a hot stage environment. I am thinking of building the frame that each LED mounts on out of 2" aluminum bar and mounting them directly to that. Trying to find a good passive way of dealing with the problem. I am also planning on running them with a relatively low duty cycle, but I want to stay conservative to make sure they last long!If I was going to go the ws2081 route, seem like using an off the shelf artnet to pixel controller would be the simplest.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 04, 2016, 10:26:48 am
content: Quote from: iampoor on March 04, 2016, 09:34:53 amSpend some time on Aliexpress to see if you can find a ready-made LED product that will do what you want - you may find something with housing and drivers for less than you can make it yourself.Also consider LED video-wall panels, which are just insanely cheap

author: botcrusher
author_rank: Regular Contributor
timestamp: March 04, 2016, 01:01:55 pm
content: Quote from: mikeselectricstuff on March 02, 2016, 07:54:04 amThere are multiple libraries, all of which are designed for using the MAX481 or another compatible chip. It would probably be easier to use one of the already designed circuits, or cop out like i did and buy a DMX shieldi'd be careful getting too sketchy, DMX doesn't have error correction, so if anything, i mean anything, makes the timing go wonky, the signal reflect, etc... Let's just say there's a reason why DMX isn'tsupposedto have pyrotechnics or rigging...

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 04, 2016, 01:19:37 pm
content: Quote from: botcrusher on March 04, 2016, 01:01:55 pmBut RS422/485 is very rugged, so not hard to get reliable data.BTW if you're generating data from your own code, DMX doesn't make sense - just use plain RS485 - higher baudrates & longer frames.A particularly simple data format is to use 0xFF as a start-of-frame and avoid 0xFFs in your data

author: iampoor
author_rank: Frequent Contributor
timestamp: March 05, 2016, 11:38:51 pm
content: Quote from: mikeselectricstuff on March 04, 2016, 10:26:48 amI have found anything even close as of yet. I want these panels to be extremely bright and low resolution. They are going to be 8 x 18 pixels and 4 x 8 feet tall respectively.I am considering using video wall panels for another display that might be tied in however. Those are so cheap I dont think I could buy the LED's for the price of the entire panel!! hahIf I could find some low resolution 2x2ft panels, I might consider them, but the large size is very important.Quote from: botcrusher on March 04, 2016, 01:01:55 pmWhich DMX shield did you buy?Im sure DMX will be robust enough for this application. My cables wont be too long (under 100ft) inbetween all 4 of these panels I would like to build.Quote from: mikeselectricstuff on March 04, 2016, 01:19:37 pmThanks for the heads up! DMX is built on Rs-485 but with a maximum baudrate of 250k right?Im assuming you use Rs-485 in most of your lighting install? More freedom when you dont have potential compatibility issues between 1000's of different fixtures I bet.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 06, 2016, 12:40:15 am
content: Quote from: iampoor on March 05, 2016, 11:38:51 pmYou should spend some time testing to see how bright they actually need to be, as this will make a big difference to cost & complexity.For a large display you may find a cluster of smaller LEDs is easier to deal with than single high power ones - heatsinking will be easier, and you can connect in long series strings to reduce voltage drop issues - maybe even avoid the need for constant-current drivers.One option may be to use square sections made of 12 or 24V RGB LED tape.

author: iampoor
author_rank: Frequent Contributor
timestamp: March 17, 2016, 05:05:09 am
content: Quote from: mikeselectricstuff on March 06, 2016, 12:40:15 amThank for the ideas. I have order some parts to assess what exactly I need brightness wise and will report back!

author: packetbob
author_rank: Contributor
timestamp: March 18, 2016, 01:31:26 pm
content: Check the DIY Xmas Lighting sites. In the forums onhttp://doityourselfchristmas.com/I know I have seen a WS2811 based driver board for 10W RGB leds. You may find other solutions.