Controlling multiple Darlington arrays with the same output pin?

Hi guys, this is a pretty basic question, but I'm just picking up the hobby again after a bit of a hiatus.

I'm working on a project whereby I'm trying to control 48 5x7 dot matrix displays. I'm relatively certain I have the shift register/Darlington array basic concept understood, but I want to double check I've approaching this right with controlling the the 8 Darlington arrays. With my setup, I'm looking to scan 7 rows across all 48 displays simultaneously. If I attempted to individually connect each input pin on the Darlington to an Arduino output, that would take 56 pins alone. Instead, I should be able to wire the appropriate INPUT1's (and 2's, and 3's, etc.) from each array together at a common node to be driven by a single output pin, correct? Is there something I've overlooking or is it really just that easy?


Without a schematic it is hard to be definitive but it sounds like you are on the right track.

I probably should have just included a diagram the first time around. :roll_eyes:

But essentially this. I'm thinking I can use a single digital output pin from my arduino to get get multiple Darlington arrays to sink at the same time, right?

Looks good to me. How many inputs are you going to connect to the one output on the arduino is it 48? You might like to check out what is known as fan out. Look at the data sheet for the darlingtons and see what input current they take. Then multiply this by 48 and see if the arduino pin can put out that much. Remember 40mA is when damage starts to occours.

Also check out in section 28 of the 328's data sheet each port's total limit.

Thanks for the help, Mike! Glad to know there's the term "fan out" associated with this sort of thing.

I'm controlling 48 5x7 displays, but each Darlington is able to sink 6 displays, so I'm only attempting to simultaneously signal 8 Darlingtons. As it turns out, the input current for the ULN2003A at 5V is only 0.5 mA, so I'm well within the acceptable limits.

Thanks again for the reassurance and imparting a bit of knowledge on me!

Here is a good tutorial on fan out