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

Hello,

I am looking for some advice, im trying to display text on a LED display and i am having some trouble trying to understand how to write a single character to one 5x7 led array. mu understanding is that i need to scan the columns at 1/n of the duty cycle. (n being the number columns). So for each duty cycle i change the data that is being supplied to rows. Im having trouble trying to understand that how could i illuminate the last row without illuminating all the leds when the columns are being scanned to quickly.

Am i right on this or completely off the ball, any tips or maybe an explanation on how the display works or how to display some sort of character would be great.

thanks in advance

Reply to
hybrid_snyper
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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.

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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?

Reply to
a7yvm109gf5d1

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:

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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

Reply to
Jonathan Kirwan

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

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obviously more than one will be connected, but one step at a time.

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.

Reply to
hybrid_snyper

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.

Reply to
hybrid_snyper

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 !

--
Baron:
Reply to
Baron

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.

Reply to
a7yvm109gf5d1

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.

Reply to
John Popelish

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.

--
 JosephKK
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Reply to
joseph2k

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."

Reply to
Jonathan Kirwan

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