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

[hybrid_snyper]

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

 

[[email protected]]

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.

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.

http://www.dfpresource.org/hdsp2000_133.jpg

Do they look like that?

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.

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?

 

[Jonathan Kirwan]

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.

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.

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.

In looking for a simple explanation I found this:

http://www.zilog.com/docs/z8encore/appnotes/an0144.pdf

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

 

[hybrid_snyper]

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.

http://www.dfpresource.org/hdsp2000_133.jpg

Do they look like that?

The product im trying to make is scrolling marquee as part of my
college course this is the LED display im wanting to use
https://www.lc-led.com/View/itemNumber/183. 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.

 

[hybrid_snyper]

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:

http://www.zilog.com/docs/z8encore/appnotes/an0144.pdf

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

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.

 

[Baron]

The product im trying to make is scrolling marquee as part of my
college course this is the LED display im wanting to use
https://www.lc-led.com/View/itemNumber/183. 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.

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 !

 

[[email protected]]

The product im trying to make is scrolling marquee as part of my
college course this is the LED display im wanting to use
https://www.lc-led.com/View/itemNumber/183. obviously more than one
will be connected, but one step at a time.

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

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.

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.

 

[Eeyore]

The product im trying to make is scrolling marquee as part of my
college course this is the LED display im wanting to use
https://www.lc-led.com/View/itemNumber/183. 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.

I don't understand what you mean. *you* have to 'strobe' it yourself in
software.

You address the display as a 5x7 matrix. Select column 1 and turn on whichever
of 7 leds is needed for the character in question, then select column 2 with the
requisite leds required for that column then column 3, 4, 5, 1, 2 and so on.

Graham

 

[hybrid_snyper]

got it, from the websites ive been looking at they start of rows
scanning through on some sort of a ring counter and sending the data to
the cathode.

http://www.acm.uiuc.edu/sigarch/tutorials/ledarray/

Im aware that the coding will control which led is lit, and the mcu
will control the strobing, ive ordered some kit to run some tests on a
single 5x7 unit. If i have anymore problems i will be sure to place my
queries in the basics group next time.

 

[John Popelish]

The product im trying to make is scrolling marquee as part of my
college course this is the LED display im wanting to use
https://www.lc-led.com/View/itemNumber/183. 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.

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.

 

[joseph2k]

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:

http://www.zilog.com/docs/z8encore/appnotes/an0144.pdf

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

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.

 

[Jonathan Kirwan]

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."