Daisy chaining pixel strips problem

[ab]

HI,
I have a number of 12v pixel strips that I wanted to daisy chain this year, in order to save on controller (advatek pixlite 4) outputs. Some strips are up to 7 meters apart and I am providing direct 12v power injection at the beginning of each strip.
Unfortunately the strip on the farthest end of the chain is not working (apart from a few LEDs flickering). As I am providing dedicated power injection I am currently thinking this is something to do with the Data signal not being transmitted correctly to the farthest strip.
Is it necessary to use dumb pixels between strips that are 7m apart in order to ensure that the data signal is generated correctly? I tried to test by creating a single pixel strip and connected between the existing larger strips but it did not seem to make any difference.
At the moment I have had to temporarily use a separate dedicated controller output to get my farthest strip working but this is not ideal.
Any advice on what I might be missing?
Thanks.

 

[buzzdude]

I would say you need a null pixel or two. I have similar long runs from a e682 and have two null pixels for the strip to work correctly,

 

[i13]

Assuming these are WS2811 strips then yes, I agree that you need a null pixel. One should be enough. It doesn't really matter how you power the null because a single pixel doesn't draw much current and therefore voltage drop won't be a problem. What concerns me is that you've tried this and it didn't make a difference.

Are you using multiple power supplies? If so then remember not to connect the positive outputs of the supplies together through the lights. You will, however, need to connect the negatives together.

 

[ab]

The null pixel fixed it thanks to you both
The mistake I made the first time was I put the null pixel at the end of the 7m cable. After your advice I cut the cable in half and made two 3.5m cables and put the null pixel in the middle - worked like a charm.
Yes I have separated the positive outputs in my power injection cables.
Thanks again and have a Merry Christmas!

 

[i13]

Glad to know that it is working. Thanks for explaining the solution.

 

[marmalade]

...wish I had bought/made some spi repeaters/buffers this year as I've found the data output of some strips to be very problematic, often not being able to traverse more than 2m. Some 2812 leds will not go more than 1m without signal integrity probs.

As a comparison, the output of the cheap pixel testers from china seem to be able to go up to 10m with the right cable, and these are just simple avr's driving a pin with no buffers.

 

[David_AVD]

I wonder if adding a small resistor (say 47 - 100 Ohms) in series at the output of the pixel (before the cable) could help?

Maybe drive current is not the issue, but ringing caused by improper source impedance?