Flickering Toward End of Chain of LED Strips

[dng]

Hello Forum. I am having trouble with erratic flickering behavior of pixels toward the end of a chain of four 150px DotStar strips. The diagram shows how they are connected. I am using the Arduino Adafruit_Dotstar library with a Huzzah32 (ESP32) controller, and a buffer chip, such that the clock and data lines are driven to 5V. (Things work fine using only two strips.)

More specifically, the flickering happens toward the end of the third strip and along most of the fourth. The flickering is always in red. Also, the last LED on each of the third and fourth strips is always on. I have swapped various power supplies and strips all along the chain, and the noise on the third and fourth strips is the same.

Here are two links to videos to illustrate.
http://projectworkshop.com/misc/MiscVid ... ndtest.mp4
http://projectworkshop.com/misc/MiscVid ... p4_5Hz.mp4

One shows the “strandtest” example that comes with the library, where I have only changed the soft SPI pin numbers, and increased the length to 600 pixels. The other shows the results of setting every fourth pixel to blue, and updating with show() at only 5Hz.

I have read that the DotStar devices have some kind of tendency to clock shift, or something, which means there is something to account for in the driving code. I am not sure about that at all, but I would appreciate any suggestions to help fix this problem.

[dng]

LedStrips.png (54.44 KiB) Viewed 121 times

Just to put a finish on this, I edited the Adafruit DotStar library file to add a little bit of delay (NOPs) related to clock and data signals, based on what I thought I saw on my scope and hints I read on-line, and things cleared right up. I completed and installed my entire system of 5 strips (750px) on the house, and it works great. BTW, if I take the delays out now, the flickering comes back. Attached is a diagram of the system now on the house. (Still have a weird pixel at the end of the string that likes to remain on (greenish) but dim, when it is not set to something bright.)