help needed to run a 5x7 led display from a mcu

How about a part number? This sounds suspiciously like the dinosaur-old HDSP displays from the 70s. They suck an enormous amount of current and require constant baby-sitting from the MCU.

Do they look like that?

Again, we need a part number. At worst, you need to write your own character generator, shift in as many bits as required, keep scanning the columns, etc. At best, you just write the ASCII characters and let the display handle itself like a grownup. But LED and 5x7 raises alarm bells, that's for sure.

You sure you wouldn't like a nice VFD display with a serial port instead?

This should be in sci.electronics.basics or else comp.arch.embedded. But I won't move the follow-ups. Just letting you know, that's all.

It does work. But I don't understand why you imagine a problem on the last row and not the others, if you imagine a problem only there. Because if you see a problem on the last row (which I don't) then I would guess you'd imagine problems elsewhere, too. But you don't seem to. So that confuses me in trying to understand your confusion.

In looking for a simple explanation I found this:

It's good enough, so I stopped looking further. Take a look starting on the 6th page of that document and work forward. It covers a fair amount of detail and I think you will understand things, after that.

Jon

The product im trying to make is scrolling marquee as part of my college course this is the LED display im wanting to use

Im just struggling to get my head around the strobing, my confusion comes from. Lets say i want the top right led lit up. I put a 1 at the last column and the rows will strobe through, whats stopping this strobing effect lighting up the rest of the LEDs below that top right one.

That is a brilliant link don't know how i didn't come across it, i'll print it out and have a good read.

You have to strobe both row and column ! A particular LED will only illuminate when both strobes coincide for that LED. Think of it like a crosspoint matrix ! Current will only flow through the two lines of a particular point !

Lots of current will be sucked by these things. Don't fool yourself. Choose the right transistors early! And lots of capacitance too.

You are. You have to continuously update the information. All you have here is a raw bunch of LEDs in a piece of plastic. You present the information you want for column 0, enable column 0. Blank the display. Present the information for the next column, enable it, blank it, rinse, lather repeat.

You light up 7 LEDs at a time, one bunch after another, continuously. What's stopping all the other LEDs from turning on is the common anode connection. You are in control of these as well. You only enable one of these at a time.

If you are talking about the light spilling over from one LED to the next, that's unavoidable, that's why there's always a contrast enhacing filter over these things. Get a piece of color gel at a art supply store, it's cheap.

Something just occurred to me. In data sheet schematic for the array, any lines that cross are not connected. Only places where a line ends at another line represents a connection. If you didn't realize that, the whole thing would look like a massive short circuit.

Why are you doing someone else's homework assignment. The whole object is for the student to learn by working it out and trying things until they undestand.

Actually, I didn't do anything of the sort. I did a simple google and pointed this college student to a very nice example case that might actually help understand the situation and was available for anyone. You might go blame the apnote writer, I suppose. In any case, if a student goes out and accesses nice teaching materials and actually learns from them, what's the problem? The point is to learn, after all. And to use what that paper says, this college student *will* have to do some important learning along the way. I'm cool with that.

So what's going on with you? One can't even point a student to educational PDFs anymore? I know, at least, that I'm not that seriously much of a straight-lace.

Jon

P.S. By the way, I've taught at universities as a professor. I am sensitive to the issue of "doing someone's homework."