Wonky colours

[cdnbob]

I have 2 sets of strings where one works fine on test pattern, and one give me wonky colours. The wonky one starts out fine but as it runs the pixels seem to start getting random colours and then gradually all shift to white as the test pattern cycles. Only the very first pixel works, and sometimes even it gets a funny colour.

I think this is a voltage problem but would appreciate any suggestions.

The setup is:
Set #1:
2 strings, lengths 68 and 52. Each string has power applied from its own DC-DC converter, power input at both the start and the end. The 2 converters are on the same PS - same +V and G. Data from the end of string 1 is fed to the start of string 2.

Set #2:
Similar: 3 strings of 50 each, again each with its own DC-DC feeding the start and end of each string. Common +V and G for each converter.

All strings are 5V strings - same make and model.

I'm thinking the 68 long string is too long for the 5V feed. But I don't understand the mechanics of what I'm seeing. Why would the problem start at pixel 2? Wouldn't there be enough voltage to get a few pixels working up front? And why start fine and then get erratic and then go to all white?

I'm going to try putting another DC-DC converter about 18 pixels into the first string. This would be a +5 injection here, or I could split into 3 strings like set #2.

Do I need to connect 5V and G between the strings?

Any thoughts and comments are appreciated.

Bob

 

[Beacy]

Need a bit more info... what sort of strings, what are you testing it with and what sort of controllers are you using.


Are the strings in each set running parallel or in series?


Have you tried to interchange the strings to see if it may actually be a faulty pixel?


All my strings are 100 pixels long powered both ends & the middle, normally when there is an issue it is a software one. BUT that depends on the pixels I only use 2801's

 

[cdnbob]

The strings are all WS2811. In each set they are in series, but the two sets are parallel. Or will be - at present I'm testing and only connect one set at a time.

The controller is an nECG-DP2 with an nPWR-DP2 for higher voltage fused outputs. I'm running 24v out to a PPR-B, configured to use the differential driver. This is how I want ot to run once put out, so I'm testing it that way indoors. I connect the PPR-B to either set and the voltage out of the PPR-B is 24.3 volts and out of the first DC-DC converter it's 5.2 volts.

I've tried both outputs from the DP2 one each set, and it's the same each time - wonky colours on set 1 and just fine on set 2.

Swapping strings isn't an easy option - the strings are mounted in a display element and difficult to remove or to cross-connect. Each string was tested stand-alone with my main controller (ECG-P12S/P12D) before it was mounted in the display, so I'm confident the individual strings had no obvious flaws on delivery.

I'm also wondering about the speed setting -I don't know if that would have a bearing here. Presently it's set to 400. I've also tried 500 (Ed's suggested value).

Bob

 

[cdnbob]

And the solution is: Speed Setting!

Once I set the speed up to 600, everything worked like a charm. It must be a combination of speed and something in the pixels, because the same output/speed worked on the 3-string set. It also worked on the 2-string set when I started after the first 18 (which were part of a 3rd string I didn't need all of). When I tried just that first 18 on its own, they wouldn't work until I upped the speed.

A very simple solution. We just won't talk about how much time was spent injecting additional power and (when that was fruitless) chasing the problem before coming up with that. :

I'm still curious about the mechanics of this. I guess it must be something to do with the IC in the pixels heating up with use, but what's happening, or not happening at the slower speed?

Anyone know what the translation is between the speed settings in the P12S and the nECG-DP2? I know the DP2 is using kbps, but I don't know what the P12S uses.

Bob