Building a very low resolution LED display

Discussion in 'The Projects Forum' started by D33G33, Oct 17, 2011.

  1. D33G33

    Thread Starter New Member

    Oct 11, 2011
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    Hi everyone,

    I'm sorry for posting right in here, all my keywords are creating such a mass of hits its making it near possible to filter out what i'm trying to achieve.

    its quite a monstrous task and I want to do as much research I can myself but if I could get some directions or link from the witty people on this forum id be every thankful.

    I am trying to basically 'build' a very low resolution LED display (TV if you will) about 50cm x 50cm. I'm hoping to be ambitious and get 1000 led's (250 x RBGY) in this area.

    So there are lots of questions around this

    How to manufacture the SMD/LEDs, PCB's and Micro Controllers (and which ones to use)

    How to project the image from a source through (???) to the LED's.

    I've seen images of it being done, I'm just not sure where to start.

    I have some basic electronic experience studying at TAFE but that was many years ago. Also once upon a time I was a jeweler and have picked up quite the steady hand and an eye for detail, not to mention patience.

    I am aware this will
    1) be expensive
    2) take a very long time and
    3) both of the above

    The panel will need to be manufacture/fabricated because the result i'm after will not be flat.

    If anyone can advise my or point me to some information regarding any of my queries I will be forever thankful.

    Many thanks in advance,
    Dayle
     
    Last edited by a moderator: Oct 17, 2011
  2. iONic

    AAC Fanatic!

    Nov 16, 2007
    1,420
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    Hello and welcome to AAC (AllAboutCircuits).

    A note on how to get the largest responses to your threads.
    Use a descriptive topic so that those who have knowledge in this area will respond to it. You Title could have been "Building a very low resolution LED display"

    Good luck with your project!
     
  3. D33G33

    Thread Starter New Member

    Oct 11, 2011
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    Thanks iONic,

    is it possible to edit my thread title?
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    It is done.
     
  5. wayneh

    Expert

    Sep 9, 2010
    12,126
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    I think one place to start is choosing the LEDs and how to arrange them. For instance, you said 50 X 50 but standard TV is 4:3. I really don't know, but your choice of aspect ratio may matter. Just something to have in mind.

    If you're planning for ~250 pixels in that area, that's only about 18 X 12 or 16 X 16 resolution. Sixteen pixels in 50cm is almost 4 cm per pixel, so unless your LEDs are huge, there will be a large empty area between them.

    Once you have your LEDs identified, you'll need to power them and you have to design on the worst case - all LEDs full on. That total power might be fairly large and will influence your power supply and the required driving circuits.
     
  6. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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  7. D33G33

    Thread Starter New Member

    Oct 11, 2011
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    This is fantastic! almost exactly what im after!

    It just needs to be slightly bigger and I need to find a way to maybe refrabricate it so that it isnt flat. (I've thought of a way i can do this buy having the flat board but extending wires from the LED mounts leading teh the LED's in any configuration I like, awesome!)

    However, this is 640 LED's. I would like to double this if I could, hopefully I can change the aspec ratio of the LED's

    Keep these coming!

    Many thanks,
    Dayle
     
    Last edited: Oct 17, 2011
  8. Adjuster

    Well-Known Member

    Dec 26, 2010
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    300
    If the OP is really planning to put ~ 1000 LEDs in a 50cm * 50cm area, that would amount to about 60W dissipation with standard 20mA LEDs, depending on colour, perhaps more if these are RGB devices and all three chips are able to be on full power.

    That could add up to a serious cooling problem, as well as an optical output sufficient to light a room if the LEDs were efficient types. The equivalent tungsten lamp power could be into the hundreds of watts. This might be too bright in fact for comfortable or even safe viewing. With some LED types diffusion is a must, or safe brightness levels may be exceeded.

    It may be more realistic to operate at relatively low current per LED, subject to the use of suitable devices, and the brightness required.
     
  9. D33G33

    Thread Starter New Member

    Oct 11, 2011
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    0

    Diffused LED's will certainly be the choice, and very unlikely that all LED's will be on at 1 time.

    It wont be used to light a room, or protect out much. It will only need to be able to be viewed in low light situations. For powering I will be exploring RC car battery packs, this is my first thought anyway.

    Thanks for the input so far everyone, this project is really exciting me.

    Dayle.
     
  10. D33G33

    Thread Starter New Member

    Oct 11, 2011
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    0
    sorry when I meant 250 x RBGY i meant
    250 x Red
    250 x Blue
    250 x Green
    250 x yellow (white)
     
  11. D33G33

    Thread Starter New Member

    Oct 11, 2011
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    After looking on all sorts of forums I found images of this project that someone has done.

    Very impressive I think!

    Does can anyone tell how they have done it from these pictures?
     
  12. BMorse

    Senior Member

    Sep 26, 2009
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    Basically they have multiple RGB LEDs strung around the "globe", each "LED" has 3 colors built into them which can produce atleast 7 different colors, so for your display, I would do the same thing, so basically 1000 RGB LED's..... That is definitely gonna be expensive... most of these displays depend on the "slowness" of the human eye also referred to Persistence Of Vision (POV), so not all LED's are actually lit at once, but the display is "refreshed" so many times per second that they appear to have multiple ones that are on at a time..... what I would do is build the "panel" in multiple segments, to make prototyping easier, make it to where multiple columns can be interconnected with each other and use some type of multiplexing scheme to drive them, you can usually store your "graphics" in SRAM, and have a controller refresh the display every so often............ but you are right, this is gonna be a lot of work, maybe you should check into LED display driver IC's to minimize the circuitry to drive that many LED's, MAXIM IC has a lot of display drivers that can be either 4 wire serial, or SPI interfaced.... >>> http://para.maxim-ic.com/en/search.mvp?fam=disp_driv&397=LED&hs=1

    I have used their MAX6952 to create a small LED matrix display >> http://www.morse-code.com/id120.htm
     
  13. Markd77

    Senior Member

    Sep 7, 2009
    2,803
    594
    It looks like there is an IC for each RGB LED, so possibly they are microcontrollers each with it's own address, controlled by a main microcontroller over serial.
    That way they don't need to be multiplexed.
    Hard to say if that's exactly what's going on from the picture.
    Impressive project and video here:
    http://uiproductions.blogspot.com/2011/07/deadmau5-led-head-replica-at-comic-con.html
    Note the build time was 10 months! Not surprising really.
     
    Last edited: Oct 18, 2011
  14. Wendy

    Moderator

    Mar 24, 2008
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    BMorse, that is pretty nifty. Ever replace the bad display? I've seen a lot of those at Tanner's.
     
  15. BMorse

    Senior Member

    Sep 26, 2009
    2,675
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    Yes, I did end up replacing the matrix with a dead "pixel"...... I guess that's what you get when ordering samples :), good thing they sent me quite a few!:D
     
  16. nickelflipper

    Active Member

    Jun 2, 2010
    280
    35
    Those displays use a serial rgb chip, commonly seen in chinese led signage strings. There are lots of different variations including an Allegro chip. Look up the Xmas forums for all kinds of information relating to driving rgb leds.
     
  17. D33G33

    Thread Starter New Member

    Oct 11, 2011
    8
    0

    This is fantastic info! those string lights look exactly what the person has used in the helmet, just rewired and mounted.

    I cant thank everyone on thos forum enough already. I have some really solid info to get going on, keep it coming.

    the build will ow most likely take place soon rather than later! After Christmas is out fo teh way I think this will be full steam ahead.

    Thanks,
    Dayle
     
  18. D33G33

    Thread Starter New Member

    Oct 11, 2011
    8
    0
    With the LED's and chips identified does anyone know what the interface is? it will ahve to be something with Arduino by teh look of it. I attached a screen capture from youtube where you can clearly see the interface on the laptop is controlling the table.
     
  19. nickelflipper

    Active Member

    Jun 2, 2010
    280
    35
    Any microcontroller will operate the serial rgb chips, but if the Arduino looks attractive, then go for it. I don't think any of those chips are going to fit under an I2C, SPI, or RS242 serial protocol. Here is the Sparkfun Arduino code to control the WS2801 chips.

    The PC interface would be using the pc's COM port, and the USB to Uart function of the FTD232R chip of the Arduino. The application software could be doing a bitmap to array transformations, then sending that data to be received into the microcontrollers data buffer. Up to a point, a lot of the work can be stored by the micro in large data tables, without the need of the pc.
     
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