I'm trying to design a 10 column x 20 row monochrome LED matrix for use as a spectrum analyzer, and after some research have settled on using multiplexing via the MAX7219 IC. I think I need 4 of them, since ceil(200 / 64) = 4.
Usually these are used to drive 8 x 8 matrices or segmented displays, and I'm trying to figure out if I need to change how I wire my matrix, or if I can just connect all the cathodes / anodes in rows and columns as usual, and use software to alter the display parameters.
I'm thinking the latter should be possible if I do the following:
Column 1: Digit 1 on IC1 Column 2: Digit 2 on IC1 etc. Column 9: Digit 1 on IC2 Column 10: Digit 2 on IC2
Row 1: Segment 1 on IC1 Row 2: Segment 2 on IC1 etc. Row 9-16: Segment 1-8 on IC2 Row 17-20: Segment 1-4 on IC3
The bottom left 64 LEDs should be easy to do, as they correspond with the digits and segments in the first chip. However, if I wanted to light the LED in the (10,20) position, I would have to send a signal equivalent to digit 2 on IC2 and segment 4 on IC3.
Now that I think about it, since there's only 30 channels (rows + columns), could I theoretically use only 2 chips (16 outputs each) to drive the whole matrix? Or will it be dim if it's multiplexed that way?
Basically, I'm wondering if I'll run into difficulties if the display isn't wired up in 8 x 8 chunks.
Thanks for your time!
edit: ok with a bit more research, I found that the digit drive lines sink current and the segment drive lines source current, so it looks like I'll need 3 ICs at least, if I can mix signals... if not, I'd love some suggestions on how to break up 200 LEDs into 4 x 50 mini matrices.