Issues with pigtails

[benhall78]

Has anyone else had issues driving strings of ws2812 LEDs from raspberry pi GPIO ports via a CD5050 chip for level conversion to +5v?
Setup
Power injection is done at the start of each string. Wire is 4 core alarm for data, 6 core (3 cores +ve, 3 cores -ve) for power. 3 strings of 150 LEDs are connected end to end. 70A 5v PSU

On the table with all the wires twisted together there were no issues providing I used the 5V from the LED power supply on the CD5050 chip. This was even with the power supply grounds (-ve) connected together. Strange but I can get over it.

Thought I had better tidy the installation up and ordered some 4 core (22awg) pigtails from eBay and connected up the data wire only. Now my issue is the signal looks like crap (noise, distortion, slow rise times) on a scope, no LED control / massive flickering / incorrect colors. To get one string working I have paired up three of the six CD5050 buffers to drive one string. Second and third strings remain uncontrollable.

The data signal degrades (on the scope) as soon as the patch cable is connected without the LEDs. The data signal gets worse as more LED strings are connected.

Any thoughts???????

 

[AAH]

The CD4050 (not CD5050) isn't a great choice as a voltage level converter as standard 4000 Cmos IC's are pretty slow and have low output current. The use of a 74HC245 or even better a 74AC245 is what I would use personally. The AC series have higher output current which is what is desired when driving into the capacitance of cable. As a simple fix a null pixel right at the Pi should do the level conversion (just) to get you from 3.3V to 5V.
Depending on the length of the cable run the 8.25A that the 150 pixels will draw at full white may be beyond what the security cable can supply. Chuck a meter on the end of the cable. A voltage drop of 10% is where you start getting issues.

 

[benhall78]

I have removed the pigtails and soldered the data wires in. No problems now. I will look for better pigtails / connectors in the new year. I will use these ones for dc switching.
It looks like i will need to add a null pixel as the run was slightly longer outside.
No problems with voltage drop.