Hi,
I'm designing an 8x8 LED matrix controller, however I'm not sure on the best/most efficient way to drive the LEDs.
They are common cathode matrix arranged LEDs in 8 columns and 8 rows. I want to use a load of "ULN2804A" transistor arrays I have which are darlington NPNs I think.
I want to scan the columns across from left to right, using a 4017 counter to 'select' a column, and then the transistor array to turn on the row circuit as needed for each column. I also want to be able to 'select' a display, as I will be hoping to easily expand the 8x8 to be many units wide. Thats why I'm thinking of maybe a counter that I can expand so it can scan columns from 1 to say 32, just by getting a clock pulse.
Whats the best setup of transistors and LEDs to use, I'm thinking a resistor on each row just after the transistors to limit the current and make an even light across each LED regardless of how many are lit at a time. Obviously persistance of vision and refresh speeds comes into play here, but I'm not worrying about that for now, just the basic drive hardware.
Thanks