LED Matrix Question

[T.Jackson]

Those LEDs in the matrix arrays are very efficient. You'll get "satisfactory" light output from only 2-3mA for ea LED. The 74LS138, if you sink current from it, it might be adequate enough.

[Dave]

mekohler, Like I said in my earlier post, What are you going to use to source the current to the paralleled led strings?

Dave Purola,
N8NTA

[mekohler]

mekohler, Like I said in my earlier post, What are you going to use to source the current to the paralleled led strings?

Dave Purola,
N8NTA

I'm new to all of this. I thought thats what the ULN did. Pretty much what you see in my last post with the 2 pictures is all I have. I wouldn't know what else to add and in what config.

[T.Jackson]

There is no need to buffer the rows (the PIC end) - this isn't the weak entity. It's the columns that may need the boost.

[mekohler]

There is no need to buffer the rows (the PIC end) - this isn't the weak entity. It's the columns that may need the boost.

agreed. would adding another ULN to the column make a difference

[T.Jackson]

Personally, I think the diagram that Sayzer posted might be right down your alley for what you need. (it looks quite correct) Bout the only thing I'd add to it is - some current boosting for the columns (if I wanted the display really nice & bright) Handful of BJT's or couple of UNL2003 would do nicely.

[mekohler]

Personally, I think the diagram that Sayzer posted might be right down your alley for what you need. (it looks quite correct) Bout the only thing I'd add to it is - some current boosting for the columns (if I wanted the display really nice & bright) Handful of BJT's or couple of UNL2003 would do nicely.

The only thing he does differently is use a 4 to 16 decoder though (?).