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
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