LED Marquee Concepts

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Hi Folks,

I'm playing around with a few project ideas and I think I'd like to build an LED marquee sign. Probably 8 rows by a large number of columns (80 columns perhaps).

Searching through google and these forums I've received a few insights. This webpage has been of help as well:
http://www.microsyl.com/

So, here's how I understand it:

* 1 8bit port of the microcontroller will control the 8 rows of the display. These will probably be buffered with mosfets or an led-driver.

* Each column will be controlled by one pin of a register shifter (probably hc595).

So to make this work, only one column will be lit at any given time. Does this sound right or am I missing a key part of this concept?

Thanks!

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That all depends on the type of marquee you are looking to design.

Is it a simple one color scrolls left, or a full featured picture system?

One thing I have always seen in the marquee style is an FPGA or cpld to lower the chip count as well as wiring. Either device can hold many of the 595's with room to spare. And there is no interconnectivity to deal with.

Sounds like a fun project.

Jim

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Only one row is lit at any time. Usually they are scanned from lower to higher rows, so that the characters are slanted to the right.

I made a small one with 64 columns or so.

I also have a big commercial LED message sign which is controlled by a 8039 :) (which is kaput btw) and just plain 74LSxxx ICs.

I don't see the advantage of a FPGA, you end up with connections from everywhere concentrating at one point; while with a string of HC595s you can keep everything local, only 4 wires that go from '595 to '595.

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jayjay1974 wrote:
Only one row is lit at any time.

Interesting. If you drive the LEDs at 15ma and have a sign with 64 columns then there is a possibility of needing 0.96A of current at any given time. Is that right? What would be a good power source for providing that kind of current potential?

This does make a lot more sense, I had it in my head that the columns would be scanned one at a time.... that would take much too long for the display to appear stationary.

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The 0.96 A current is correct. The power is at tht upper limit of the wall plug powersuplies.
15 mA per LED is not realy much für the LEDs. Because the are on only 1/8 of time they will be as bright as at about 2 mA, so you probably want to look for high eficiency LEDs, not the very cheap ones. On the other side 15 mA per Pin is slightly above the rated total current for a HC595. It will probably work, but do not use it for a commercial product, or if you need high relibility / durability.