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gt401967
08-18-2005, 08:42 AM
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

Chris Savage
08-18-2005, 09:10 AM
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

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Chris Savage
Parallax Tech Support
csavage@parallax.com (mailto:csavage@parallax.com)

Paul Baker
08-18-2005, 11:41 AM
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.

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·1+1=10

knightofoldcode
08-18-2005, 12:07 PM
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 Savage
08-18-2005, 10:12 PM
Paul,

·· Nice catch.· I didn't even do the math!· http://forums.parallax.com/images/smilies/idea.gif

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Chris Savage
Parallax Tech Support
csavage@parallax.com (mailto:csavage@parallax.com)

Paul Baker
08-18-2005, 11:27 PM
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.

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·1+1=10

Bean
08-19-2005, 01:06 AM
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.

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"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 (http://www.sxvm.com)

"One experiment is worth a thousand theories"
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Peter Verkaik
08-19-2005, 06:09 AM
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

Steel
08-19-2005, 06:24 AM
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.

Bean
08-19-2005, 08:14 AM
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 (http://www.sxvm.com)

"One experiment is worth a thousand theories"
·

gt401967
08-24-2005, 05:12 AM
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