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

 

ok I don't think I explained myself very well there:

I have a load of ULN2804A transistor arrays. I want to drive a grid of 8x8 LEDs, what is the connections I should use and should I have resistors (and what values) on the control pin of the transistors so I can drive them from other logic circuits? I need to be able to control rows and columns seperately for each row/column so I will need transistors on the rows and columns right? The LEDs are just standard red LEDs arranged in a usual matrix.

Thanks

 

some articles are posted here regarding muliplexed displays . a search would be better .

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