More LED Matrix help

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Jon
Posts: 42
Joined: Thu Jul 06, 2006 12:43 pm
Location: downUNDER

More LED Matrix help

Post by Jon »

In the document AN1, 'Using IO Warrior with LED Matrix', there is mention of using the ULN2803 in conjuction with the 74xx595 for the Row drivers. Would someone be able to supply a sample circuit of the output side of the 595, showing how to connect the ULN2803 to the matrix.
From what I can see, a signal on a pin of the 2803, will pull the corresponding pin to ground, but dont we require that pin to supply current to the matrix?

Regards Jon
Jon
Posts: 42
Joined: Thu Jul 06, 2006 12:43 pm
Location: downUNDER

Post by Jon »

Anyone?
wayoda
Posts: 362
Joined: Fri Dec 19, 2003 12:00 pm
Location: Wuppertal/Germany

Post by wayoda »

Hello Jon,
I'm really not an expert in electronics, but I had a look at the datasheet of the ULN2803.
This looks like an error in the Application Note.

I think it could be used as replacement for the 5821 column driver but not for the 5891 row driver as suggested.

Eberhard


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wayoda
Posts: 362
Joined: Fri Dec 19, 2003 12:00 pm
Location: Wuppertal/Germany

Post by wayoda »

Hello Jon,

I found the UDN2585 from Allegro which could probably(???) be used as a replacement for the ULN2803 in a row driver.

But at least in Germany it's almost the same price as the 5891 integrated version.

Do you have problems getting the 5891/5821 or are you looking for a cheaper alternative.

Eberhard
Jon
Posts: 42
Joined: Thu Jul 06, 2006 12:43 pm
Location: downUNDER

Post by Jon »

Thanks for the reply.
I have decided on using transistors as I want to start production of the board. (Ive designed a double sided PCB which incorporates the chips to run a 8 x 32 LED Matrix)
Had no trouble getting the 5821's , I ordered them from Segor along with the IOW 40. Took only 1 week to arrive, I was very happy. In Australia I found the 5821 for AUD 18.00 , much more expensive than Segors. The reason for attempting the ULN2803 was for the power requirements needed by the matrix.
But I will look into the UDN2895

Thanks
wayoda
Posts: 362
Joined: Fri Dec 19, 2003 12:00 pm
Location: Wuppertal/Germany

Post by wayoda »

Hello Jon,

I really don't want to discourage you, but I stumbled upon an interesting alternative to the IOWarrior40's LedMatrix mode:

It's the MAX7221 produced by Maxim.
The chip is capable of driving 8 7-Segment Led-Displays (common cathode) and can controled via SPI-Mode of the IOWarrior24. (Which might be bad news for you
because IOWarrior40 doesn't have the SPI-Mode)

The maxim-website has a datasheet and application notes
http://www.maxim-ic.com/

This is all theoretical but the advantages for this solution could be:
Smaller PCB; only 1 MAX7221 and 1 resistor is needed for an 8 digit-module
It should be possible to daisy-chain 3 modules. (which makes it a 8x24 matrix)
In germany the cheapest price for an MAX7221 in DIP-Package is 8.80 EURO (something like AUD 15.00). This is silghty more than the 5891/5821 solution but with the smaller PCB you might end up with the same production costs.

Eberhard
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