I need to drive 80 RGB leds (so 240 individual leds), physically and conceptually aligned as an 8x8 matrix + an additional vertical line and an additional horizontal line.
I'd like to drive the matrix using 595 shift registers, so that I only need 3 microcontroller lines to drive all the leds, multiplexing the leds. The RGB leds I'm using are common anode. I'd like to have at least 3 levels of brightness for each color (full off, half on, full on).
I found many examples of driving an 8x8 RGB matrix with shift registers, but I'm trying to understand what's the best way (code-wise, mainly) to add the additional 16 RGB leds.
Option 1: a 9x9 matrix. If so, the additional column pin and additional row pin would come directly from the microcontroller and not from and additional shift register, since a shift register for only 2 pins would be wasted.
Option 2: a sub matrix in series with the first, that shares the anodes with the main matrix, but uses only an additional shift register to drive the additional cathodes. Other options?
thank you and sorry for my bad english.