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I have this sample code:

#include <MD_Parola.h>
#include <MD_MAX72xx.h>
#include <SPI.h>


#define MAX_DEVICES 4
#define CLK_PIN   11
#define DATA_PIN  12
#define CS_PIN    10

MD_Parola P = MD_Parola(DATA_PIN, CLK_PIN, CS_PIN, MAX_DEVICES);

void setup(void) {
  P.begin();
  P.print("PPPPPPPP");
}

void loop(void) {
}

And this is how it lights up the display:

enter image description here

I presume that the code displays text incorrectly, because the display manufacturer has connected individual 8x8 displays "differently than any library expects" (i.e. in red I have annotated the column addresses for my display, while with green I have annotated what they would have to be for this library to show text correctly).

I have two questions:

  1. Is there any good Arduino graphics library that would allow me to fix from software the addressing issue specific to my display?
  2. Since in the future I plan to make a 16x64 display out of 4 of these, then is there a library capable of doing that as well (i.e. have vertical font size of 12-16 pixels)?
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3
  • No software will work properly when hardware doesn't.
    – Ignacio Vazquez-Abrams
    Dec 3, 2017 at 20:26
  • @IgnacioVazquez-Abrams I imagine that if there was graphics library that would allow me to render pixels in memory buffer instead of hardware directly, then I could compensate this hardware bug by using LedControl library and calling something like setColumn((7-addr&0x7)+addr&252,value). So is there a library that allows to render pixlels in memory buffer?
    – user2138912
    Dec 3, 2017 at 20:35
  • This may help. It's hard to say if you have bad hardware or a bad library.
    – Nick Gammon ♦
    Jan 3, 2018 at 6:11

1 Answer 1

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1

The issue is minor. It looks like the library was designed for a slightly different matrix display / wiring.

Take a look at the library and it likely maps the input buffer to segment / dot-matrix information. Play with that.

The author did 99% of the work for you. You just need to finish the last 1%.

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2
  • You mean to change the code in library itself? This somewhat puts maintenance burden on me to share a fork of patched Parola library with my code until I get these Parola changes upstreamed and downstream (ie. Arduino Web IDE) picks them up. So I would prefer to use a library that can deal with this issue out of the box, if there is one.
    – user2138912
    Dec 3, 2017 at 21:01
  • 2
    the solution is really simple: swap bit orders. so you just need to write a function that swaps bit 7 <-> bit 0, bit 6 <-> bit 1, bit 5 <-> bit 2, bit 4 <-> bit 3. very easy to do.
    – dannyf
    Dec 4, 2017 at 1:55

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