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LPD8806 Clock rate
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LPD8806 Clock rate

by timistof on Mon Sep 12, 2011 5:17 am

Hi Everyone,

Has somebody tried to boost the clock frequency of a LPD8806-controlled led strip? I'm planning on doing a project where I need to control a lot of these strips (for about 3000 leds worth), and would like to have a decent "refresh-rate". On a standard Arduino-Uno the clock rate seems to be about 65 khz. I'd like to make this as fast as possible, using an STM32 with fast GPIO / SPI ports.
Also, does anyone know how much of these strips you can daisy-chain together? I can imagine that the current can get quite high on longer runs.
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Re: LPD8806 Clock rate

by kch on Mon Sep 12, 2011 7:15 am

I did some work on the WS2801 library and used the hardware SPI to get the per-pixel time down to 27.5uS. The LPD8806 looks quite similar in the way it works from my quick look at the code.

If you can incorporate my code into the LPD8806 library, you may be able to get a reasonable frame rate.

My post is in the forum here (WS2801 Speed Improvement & Code Additions). Look at the "show()" function and the SPI library stuff.

Sorry I can't help more, but I don't have these pixels to test with.
ph1x3r
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Re: LPD8806 Clock rate

by timistof on Mon Sep 12, 2011 11:12 am

Thanks! That looks promising. Indeed these controllers look alike, I just hope the chinese have done a very thorough job imitating this chip :)
I'll be using the 2 spi ports of the STM32 / Maple, which is able to run spi up to 18 mhz.
I think I'm just have to going to order a strip to see how fast I can push it.
I'll post something as soon I have some results..
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Re: LPD8806 Clock rate

by kch on Mon Sep 12, 2011 10:52 pm

If you *really* want to push the limits of the device, then take a look at the FPGA dev board that was just announced. These are the devices that are normally used to drive very large LED arrays as they can do lots of things in parallel.
ph1x3r
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Re: LPD8806 Clock rate

by cjbaar on Sat Sep 17, 2011 12:53 pm

FYI... I just posted a modified version of the LPD8806 library that uses native SPI. It takes advantage of some of the modifications to the WS2801 library made above by ph1x3r. It isn't quite as fast as the 27.5us-per-pixel refresh, but it comes close. Depending on the number of pixels being changed, I have gotten down to 37.4us-per-pixel on a 160-LED strip, using an Arduino Uno at 16MHz.
http://forums.adafruit.com/viewtopic.php?f=47&t=22982

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