Shop OBEX P1 Docs P2 Docs Learn Events
Led matrix — Parallax Forums

Led matrix

gt401967gt401967 Posts: 2
edited 2005-08-23 21:12 in BASIC Stamp
I’m new to Basic Stamps. Is it possible toto control a matrix of LED’s that is say 32 X 32 using pulse width modulation? I am trying to make an array of RGB Luxeon LED’s that will allow me to control the intensity of each LED independently. Any suggestions/input helps.
Thanks

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-08-18 01:10
    Hello,

    ·· Here are a couple of threads you could check out...

    http://forums.parallax.com/showthread.php?p=545620

    http://forums.parallax.com/showthread.php?p=539830

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • Paul BakerPaul Baker Posts: 6,351
    edited 2005-08-18 03:41
    I dont think you'll be happy with the results trying to do most/all of it on a stamp, thats over 3K elements to control, with the stamp doing only a few thousand commands per second, youll see only a black screen because the brightest a pixel can be is 1/3000th its maximum intensity. This would require a much faster external circuit/processor.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    ·1+1=10
  • knightofoldcodeknightofoldcode Posts: 233
    edited 2005-08-18 04:07
    Paul Baker said...
    I dont think you'll be happy with the results trying to do most/all of it on a stamp, thats over 3K elements to control, with the stamp doing only a few thousand commands per second, youll see only a black screen because the brightest a pixel can be is 1/3000th its maximum intensity. This would require a much faster external circuit/processor.

    Paul,

    At first glance, 3K seemed way too high, after the math, I was amazed to see that it was that high. I think gt401967 might not have realized this huge task. Especially for the slow BS2's.

    Knight.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-08-18 14:12
    Paul,

    ·· Nice catch.· I didn't even do the math!· idea.gif

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • Paul BakerPaul Baker Posts: 6,351
    edited 2005-08-18 15:27
    Now you could do a direct drive by employing 128 darlington arrays and 128 registers (pretty scary huh?) but you still wouldn't have brightness control beyond off/on. Now if you replaced the registers with shift registers and used a SX (probably need more than one) to drive the data going into the shift registers, you can get the full brightness control you are seeking.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    ·1+1=10
  • BeanBean Posts: 8,129
    edited 2005-08-18 17:06
    I would be happy if I could drive an 8x8 RGB matrix with 16 levels with a single SX48 chip.
    And by-God, I'm going to try it as soon as I get a chance.
    Bean.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    "SX-Video·Module" Now available from Parallax for only $28.95

    http://www.parallax.com/detail.asp?product_id=30012

    Product web site: www.sxvm.com

    "One experiment is worth a thousand theories"
    ·
  • Peter VerkaikPeter Verkaik Posts: 3,956
    edited 2005-08-18 22:09
    Bean,

    Some quick calculations on a 8x8 RGB led module with a SX48 or SX52.

    Assuming a RGB led has four connections, connect the leds in a matrix like

    a matrix keypad, but with 3 levels. Requires 4x8 = 32 pins. Instead of using PWM,

    use a timed switch (one led on at a time) like scanning a matrix keypad. Take 3 rambytes

    per RGB led, total is 64x3 = 192 bytes. Plenty of ram left to implement the switching.

    (the leds are illuminated like a TV screen, one dot at a time).

    The SX48/52 protoboard is ideal, the 32 pins for led control can be wired to a 2x17 pinheader in

    the pad area. Mount the 64 leds on a pcb with 2x17 header. Connect both headers with

    34pin flatcable. Combine multiple of those modules to create a larger·led array.

    I would go for the SX52. Then you have 8 pins left for module selection, I2C I/O or serial I/O.

    regards peter
  • SteelSteel Posts: 313
    edited 2005-08-18 22:24
    I am working on the same thing with a mere Red LED matrix of 14x10. Even with that number of LEDs, I am finding intensity issues.

    I did have the BS2 hooked up to 3 74595 Serial/Parallel registers.

    With the matrix being multiplexed, you can only run 1 row of LEDs at a time. This would take the PWM already down to 1/10. (10 rows).

    I am still working on a solution that will send frames fast enough that the PWM is not visible.
  • BeanBean Posts: 8,129
    edited 2005-08-19 00:14
    Actually I was going to attempt 24 PWM outputs and scan each column. for 1/8 duty cycle.
    Bean.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    "SX-Video·Module" Now available from Parallax for only $28.95

    http://www.parallax.com/detail.asp?product_id=30012

    Product web site: www.sxvm.com

    "One experiment is worth a thousand theories"
    ·
  • gt401967gt401967 Posts: 2
    edited 2005-08-23 21:12
    So it would appear that a basic stamp would not be well suited for a large arrary of LED's. Does anyone have any suggestions on where else I might look?
    Thanks
Sign In or Register to comment.