Hello
Question. I have a MAX 7219 driving several LEDs. I have two LEDs in parallel with each other on the breadboard. They both work as design both flashing in unison. When I move them apart from each other but still the in parallel to each other one flashes the other stays on. The distance is about 20 feet. I have double check my wiring. I have noticed that the one away from the breadboard does dim when the one on the board is on.
There are limits to cable length.
Are you use SPI.
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I have two LEDs in parallel with each other on the breadboard.
Having LEDs in parallel without any external resistors is a bad idea, they will not share current equally. Added to that you are running one on the end of a long wire. The rapid changing in signals that is the multiplexing will tend to get "smudged" over a long wire. Basically don't do it, or do it properly with line drivers at both ends, which will be more trouble than it is worth.
Thank you both. After I posted I thought about that. Will let you know.
I'm sorry. I'd said I'll let you know and I never got back to you. Yes it was too long. I shorten to 1 foot and it worked much better. Thanks