Help with RGB LED Pixels (LPD6803)

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dcarmean
 
Posts: 5
Joined: Mon Jan 04, 2010 1:13 am

Help with RGB LED Pixels (LPD6803)

Post by dcarmean »

I'm trying to get the digital RGB LED Pixels (LPD6803) to work and I'm doing something stupid that is escaping me. Please help.

These are the LED strands that I'm trying to get working:

http://www.adafruit.com/index.php?main_ ... cts_id=307

So, I wired up a strand, connected it to an Arduino and loaded up the strandtest sketch that came with the LPD6803 library. When I power everything up, the pixels come on in a random state, but never change as the sketch executes. They are in a static, random state (some off, some yellow, some red, etc). If I power cycle the setup, the colors will change on power up, but do not cycle as the sketch is executing.

Since I'm sure it is something stupid, I wired up a second strand on a completely different Arduino in an attempt to make sure I don't have something bad in the first setup. The second setup (completely different LED strand, completely different Arduino) behaves exactly the same way - static LEDs in a random state.

I hooked up a logic analyzer to the data and clock pins, and it appears that the clock/data pins are at least wiggling as I would expect. The clock is running at 25kHz, with a 12.5% duty cycle, which seems in the ballpark. I've attached a screen capture of one of the logic analyzer runs.

I've tried powering the LED strand off of a separate supply (properly grounded) and off of the Arduino supply with exactly the same results.

It must be something stupid, but I'm at a loss. Any thoughts?
Attachments
logic.png
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jgotthardt
 
Posts: 33
Joined: Mon Dec 03, 2007 11:58 am

Re: Help with RGB LED Pixels (LPD6803)

Post by jgotthardt »

Try connecting the clock and data signals at the other end of the string.

adafruit
 
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Joined: Thu Apr 06, 2006 4:21 pm

Re: Help with RGB LED Pixels (LPD6803)

Post by adafruit »

we have a tutorial coming soon! but yeah, there is a 'direction' look at the arrows on the LEDs :)

thedeepfriedboot
 
Posts: 24
Joined: Wed Dec 02, 2009 1:02 am

Re: Help with RGB LED Pixels (LPD6803)

Post by thedeepfriedboot »

If you are still having a problem with the LEDs, the solution might be simpler than you think. Connect the ground of the power supply powering the LED strand to the microcontrollers ground connection. Serial connections need a common ground in order to get a clean signal through. Just make sure you have the common ground set up and see if that works. I had this exact same issue with my LEDs and this fixed it right away.

dcarmean
 
Posts: 5
Joined: Mon Jan 04, 2010 1:13 am

Re: Help with RGB LED Pixels (LPD6803)

Post by dcarmean »

My problem was with the arrows on the LEDs (wow). The arrows are pretty subtle. It would be a good to emphasize the directionality of the strands in the tutorial.

I'm surprised that I wired both strands from the wrong end. I guess there is a 25% probability of doing getting both strands wrong, and I did it.

Anyway, thanks for the help - I'm up and running now.

adafruit
 
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Joined: Thu Apr 06, 2006 4:21 pm

Re: Help with RGB LED Pixels (LPD6803)

Post by adafruit »

we will! good to see you got it working :)

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