I cannot believe how great your system is. I have no electronic experience, and this is awesome. But...
I have 5 7219's, and 2 1637's on a MUX board. The 1637's work flawlessly, but all the 7219's have the same problem. They all go wonky when data comes their way. For example, if I turn the speed encoder 1 click at a time, i will get 2 or 3 knots increase, then extra segments begin to light up, then all the segments and decimals light up. Or it blanks out. If I do it quickly, the problem is instant. Does not matter if I use my hardware encoder, or the one on the virtual panel (zibo 737). I have tried pulldown resistors from 470ohm to 6.6k. I have tried onboard 5v from mega, external power supply...no difference. All my grounds are bussed together. Ive changed 7219's, rerouted wiring, unplugged all but one, tried different 4067, no improvement. If i don't change anything, it will display properly for hours. The effect only happens when i change the affected value (hdg change wont mess altitude display) so it doesn't seem like noise. Resetting config on the status popup resets them properly, til I turn the knob again.
As i said, the 1637's dont have this problem. Should I put pulldowns on unused MUX output pins?
Keep up the great work.