Super beginner request for help! I want to achieve 2X LED density in a

Bill_Davison · April 8, 2018, 11:04am

Super beginner request for help! I want to achieve 2X LED density in a POV project I’m building for my son. I sized everything out and two 2020 LED strips adjacent to one another, offset by one LED-width fit perfectly with no overlap. It’s doable!

I have successfully built one POV baton using Mortonkopf’s build log and code (code linked below), but my just-starting-out programming skills have no hope of modifying the POV function to address the image array data to two separate, offset, alternating-as-you-ascend LED strips.

If this is the kind of thing that can be reasonably accomplished with some elegant (or hack-ish) code, I would really appreciate the help!

My starting point code-wise is here.

Thank you.
https://pastebin.com/SeYY4MCx

marmil · April 8, 2018, 2:37pm

If I understand correctly, you have two strips arranged side by side like this:
0_1_2_3_4…
_0_1_2_3_4…

And you want the data sent to them like this:
0_2_4_6_8…
_1_3_5_7_9…

If you code as if you had a single strip of double length, NUM_LEDS x 2, then you can call a subroutine right before calling FastLED.show() that copies and shuffles the pixels into the correct final display ordering.

Bill_Davison · April 9, 2018, 8:33am

Correct - that’s a much simpler way of putting the problem!

When you refer to NUM_LEDS x 2 are you saying to use the sum of the LEDs on both strips as my NUM_LEDS figure? (That makes sense.)

Can you point me to an example or two I can draw from regarding the subroutine that copies and shuffles the pixels into the correct final display ordering? I’m not quite sure where to begin on that. (I was just reading about CRGBArray and CRGBSet. Will those be applicable here?)

Thank you!

marmil · April 9, 2018, 7:38pm

Here’s a shuffle function you can try out:

gist.github.com

https://gist.github.com/marmilicious/fe0bbb5a381930a77188dfa5e0b244a5

shuffle_function.txt

For Bill from this post:
https://plus.google.com/u/0/109149766109138486006/posts/J9Xnqthpgsh
//---------------------------------------------------------------


Somewhere at the top of the program:

#define NUM_LEDS 32  //length of one strip
#define DBL_LEDS NUM_LEDS*2  //double the length of one strip
CRGB ledsA[NUM_LEDS];  //strip A (gets displayed)

This file has been truncated. show original

Bill_Davison · April 12, 2018, 3:44am

Thank you, Marc! I’m going to give this a shot tonight!

Bill_Davison · April 13, 2018, 9:32am

Good news and bad news!

The good news: I built a small test setup, with offset adjacent rows of 8 LEDs each. I incorporated your code into the POV sketch I had been using and it worked!

The bad news: I tried scaling it up to 300 image “slices” and two adjacent rows of 98 LEDs each. Result: Arduino IDE wouldn’t compile my sketch, returning “out of scope” errors for the PoiSonic and ShufflePixels functions. I do have a pretty neat setup, though, of 198 APA102 2020 LEDs crammed into ~20".

Any idea what’s going on with the compile errors? I tried loading the sketch on a Teensy 3.2, and I have plenty of other boards available.

Code: https://gist.github.com/bdavisonhelo/da4527406d7109e51a55e5776a6d2189

Thanks again!

marmil · April 13, 2018, 4:51pm

Oh wow that’s a long line, haha.
I didn’t get the error you got, but rather a “not declared in this scope” error. So I reordered a few things and then it compiled for me on a Teensy 3.2 After line 31, I first put the ShufflePixels function, then the PoiSonic function, and then put the main void loop at the very bottom.