I see in the documentation you can not "daisy chain" MAX7219 LED displays. From what I understand, if I want to use 2 or more, I need to assign a pin (CLK) for each display. If that is true:

Pin #27 "L" is shared between the 2 MAX7219s

Pin #28 "D" is shared between the 2 MAX7219s

Pin #30 (CLK) for 1 MAX7219

PIN #31 (CLK) for 2nd MAX7219

My Config:

N30 D=0 B=1,10 b=0
N31 D=0 B=1,10 b=0
N31    Nav1_Active       o=2
N30    Nav1_Standby    o=2

When x-plane loads, I see they display correctly:

Once I change the stand-by freq, the second MAX7219 gets screwed up:

My question is, do I need a 74HC4051 8-Channel Multiplexer board or am I doing this incorrectly?

** EDIT **

I was able to get this working by double checking my connections. I also noticed you can't turn the encoder too fast or its screws up the display. Nevertheless, pretty cool how it all works with relative ease. 

closed with the note: Issue was wiring
Sep 18, 2019 in 7-Segment Displays by

1 Answer

Best answer
Eventually, all such problems for most cases was in wiring and power source quality. The encoder should NOT influence the display.
Sep 21, 2019 by
Thanks - you are 100% correct.