AT90S8515 interface to 8X8 LED display

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I am looking for suggestions on interfacing a ATMega8515L or theAT90S8515 device to a 8X8 LED display.
I have one of LED display's laying around and would like to make a scrolling clock display.

Searching the Internet, I found many projects that use the Max 7219 device. I did not want to use that chip. However, I am thinking that I can use a ULN2003 to control the cathode side as a row driver and then send the 8 bits per row from a selected
8 bit port. This means that each full character must have 8 each 8 bit patterns associated with the character.
I don’t see any advantage in using a X/Y coordinate approach but I am not sure, is that even a way to consider?

Looking for suggestions…..
Thanks Freaks.

I'll believe corporations
are people when Texas executes one.

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If you're running multiplexing, then current sourcing/sinking becomes a problem. That's why the 7219 is used - it does all the work. Using a uln2003 (or uln2803-8bits) is fine for the current sink, but you'll need transistors/mosfets or a source driver ic like a udn2981. Reson is that say you're running a 1:8 multiplex - a given led is only on for 1/8 of the time and not as bright, so you have to pulse more current to regain the brighntess. so, instead of 20mA, we're talking 8 times that - 160mA which the AVR port pins are not going to source.

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Concerning the current, If I use a ULN2003 to sink current for a common cathode, then use current limiting resistors for the anode segments, I am thinking that the '2003 can sink the current. Couldn't the uP handle the 20 mA per segment?

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tubecut wrote:
Couldn't the uP handle the 20 mA per segment?

What does its datasheet say?

Markus

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Kartman: I looked at the UDN2981 data sheet but I am not sure if I am interpreting the data sheet. If it is what I see it as, then pin 9 is the input for the 'high voltage' such as +12 VDC for the LED's. Then a logic one at the input pins turns on that particular output?
Thanks for the tip on using the ULN2803 , 8 bits, takes care of not adding another '2003!
Once again, thanks for the assist.

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Quote:
such as +12 VDC for the LED's.Then a logic one at the input pins turns on that particular output?
Correct, or whatever voltage you may put there 6V,7V. Remember that some displays have a few leds in series and therefore you will need more than 5V feeding the led strings.

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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OK, yes, I think this one (8X8) may have two in series.
I think I will need separate power for the LED's as I will use the Olimex PCBA which only has a 7805 regulator.
Thanks for the help.

I'll believe corporations
are people when Texas executes one.