LPD8806 LED RGB strips in parallel

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happyinmotion
 
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LPD8806 LED RGB strips in parallel

Post by happyinmotion »

Hi All,

I'm wanting to run two LPD8806 strips that display exactly the same output. I'm also wanting to do this as fast as I can and in the minimum space possible. Can I just connect my Arduino to both strips in parallel so both respond in the same way to commands from the microcontroller?

Ideally, I'd like to avoid having to send the data separately to the two strips. Alternatively, if I daisy-chain the strips so that they appear to the microcontroller as one strip of twice the length, what will be the fastest way to copy the data in the first half of the strip to the second half? How much is it going to slow down each refresh?

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pburgess
 
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Re: LPD8806 LED RGB strips in parallel

Post by pburgess »

Yep, feeding the same clock/data to multiple strips works just fine.

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happyinmotion
 
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Re: LPD8806 LED RGB strips in parallel

Post by happyinmotion »

That's excellent news.

There are two strips in the post to me right now, I'll be able to confirm that this works next week or so.

jrt
 
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Re: LPD8806 LED RGB strips in parallel

Post by jrt »

I found this thread as I am trying to better understand the Arduino/LPD8806 before I try it.
I am having trouble understanding how LED 'addressing' is handled.

First, if I desire to have a number (ex. 5) of independently controlled (ex. short 5") strips, would I be better off using multiple Arduino output pins or would I be better off to daisy chain wire them in series?

Secondly, how does any single segment know what 'address' a particular LED is? That is, if I have two separate strips, it seems like the first LED on each would be #1.
Does #2 know it's #2 by virtue of some counter that is decremented as the signal passes through each segment?

thanks for any insight..

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adafruit_support_bill
 
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Re: LPD8806 LED RGB strips in parallel

Post by adafruit_support_bill »

The leds on a strip are daisy chained. The first led in the chain is always #0.

If you chain two strips end-to-end, the addressing for the second strip continues from the first.
If you connect two strips in parallel, both start at #0.

jrt
 
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Re: LPD8806 LED RGB strips in parallel

Post by jrt »

Thanks for the quick response!

I am an Arduino newbie, but wondering if you might you have thoughts on using LPD8806 strips along with a touch screen/shield for control?
I thinking one could be used to select a particular segment , choose it's color from a palate, and set the brightness.

In a non-daisy chained setup, do you think I could I include such a device along with using say 5 independent segments? (using 10 output pins).
I'm thinking the daisy chained path may be easier from a control perspective (2 pins) (and more responsive?) with physical wiring/troubleshooting being the trade-offs.

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adafruit_support_bill
 
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Re: LPD8806 LED RGB strips in parallel

Post by adafruit_support_bill »

Sounds like a fun project!

Either implementation would work. Individual strip updates would be slightly quicker with a parallel arrangement. Multi-strip updates might be slightly quicker wired in series. However, unless you are talking about some very long strips I don't think you would notice any difference between the two.

jrt
 
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Re: LPD8806 LED RGB strips in parallel

Post by jrt »

Ok, thanks.

I was just reading about this product - http://www.adafruit.com/products/376.
The tutorial mentions : 'Uses digital pins 5-13 and analog 0-3. That means you can use digital pins 2, 3 and analog 4 and 5. Pin 12 is available if not using the microSD'

Which I think gives me my answer in that I'd have to do so in a daisy chained method, as only pins 2,3 would be available.

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adafruit_support_bill
 
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Re: LPD8806 LED RGB strips in parallel

Post by adafruit_support_bill »

You can use analog pins as digital pins, but that still only gives you enough for 2 strips. Looks like daisy-chained is the way to go.

sparr
 
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Re: LPD8806 LED RGB strips in parallel

Post by sparr »

You could use a demultiplexer to only send serial data to one of the strips at a time. This would use only one pair of pins for the serial output from the uC, and more pins to pick the target.

jrt
 
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Re: LPD8806 LED RGB strips in parallel

Post by jrt »

The demultiplexer is an interesting thought, giving me 8 independent channels.
I read a bit about using a CD4051 chip as a demultiplexer.
It seems that I would and additional 3 pins for the 4051.

Would I be able to use digital pins 0,1,4 to do this?
Digital pins:
0,1 -> 4051 S0,S1
2,3 -> Serial data (to LPD8806s)
4 -> 4051 S3
5-13-> touch screen

IceDog
 
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Re: LPD8806 LED RGB strips in parallel

Post by IceDog »

jrt wrote:Thanks for the quick response!

I am an Arduino newbie, but wondering if you might you have thoughts on using LPD8806 strips along with a touch screen/shield for control?
I thinking one could be used to select a particular segment , choose it's color from a palate, and set the brightness.

In a non-daisy chained setup, do you think I could I include such a device along with using say 5 independent segments? (using 10 output pins).
I'm thinking the daisy chained path may be easier from a control perspective (2 pins) (and more responsive?) with physical wiring/troubleshooting being the trade-offs.
I'm working on the same project, but using an Android tablet. I haven't implemented multiple strips yet, just doing the project on one first. But when I do, I plan on using a demultiplexer.

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