Since I got the code working, next I needed is to wire up individual LEDs in a matrix so it'd be possible to add them to a Christmas canvas painting. The challenge is that not all LED are equal. Red, yellow, and green typically works below 2v while orange, blue, purple, and pink is a bit higher.
Can I cheat a little and use series resistor with lower spec'd LED? All the same color will be on the same row (ie row 1 is red, row 2 is orange, etc) so I can use resistor on the 3 lower spec'd LEDs to lower the current draw on red, green, and yellow? Or would arranging color by column and using resistor in column be better?
With Max7219, one resistor sets the current for all LEDs. The chip attempts to adjust the current flowing through each led to match the current determined (indirectly) by that one resistor. If you add extra resistors into the matrix, the chip will just try to compensate for that, if it can, and you finish up with the same current again.
I would select your single resistor based on the LEDs with the lowest forward voltage and see if you are happy with the resulting brightness of all the other colours.
Point is, have you actually built the thing, or are you musing on theoretical points?
I haven't built it yet, only one MAX chip on hand and I don't want to fry it before I get a few extras on hand.
only one MAX chip on hand and I don’t want to fry it before I get a few extras on hand.
That makes no logical sense. Don’t waste time, spend that time learning using the chip you have now. Having other chips on hand won’t prevent you from frying a chip.
Yes, wire up your array and the MAX7219, if you have complaints about the brightness (which I suspect you will not), then we may have something to discuss.
"Frying" the chip is in no way related to this.
I always advise buying two or three of these kits:
Or these ones
which used to be more expensive but are now actually cheaper and more useful if you wish to stack matrix arrays.
The point is that you do not install the matrix arrays from the kits themselves - or their socket pins, but just solder to the positions on the PCB and you have a durable and reliable assembly to drive your own matrix arrays.
Why did I say two or three? Well, you can fully assemble the first one as the matrix with which it comes and practice programming it. Then the second one for your current project and the third one - for the next!
Considering the cost, it makes no sense to just buy one!