Arduino and 24 LEDs
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Arduino and 24 LEDs

by Dirkus on Tue Dec 18, 2007 6:11 pm

The Arduino looks like a fun system to play with. It has caused me to think of some things that I would like to make.

One project that has come to mind would require 24 LEDs. Is there any way to get the Arduino to handle that many LEDs? If not, is there some other programmable controller I should look at?

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Joined: Tue Dec 18, 2007 6:02 pm

Answering my own question

by Dirkus on Wed Dec 19, 2007 11:45 am

Looks like I get to answer my own question. It looks like I will need to use the Maxim MAX7219/MAX7221 matrix controller (http://www.arduino.cc/playground/Main/LEDMatrix) and the Wiring matrix library (http://www.wiring.org.co/reference/libr ... index.html)

Now to get parts and pieces and start the prototype process.
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by frank26080115 on Wed Dec 19, 2007 11:21 pm

Something else to consider, Charlieplexing

http://www.instructables.com/id/Charlie ... /?ALLSTEPS

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Joined: Fri Jun 15, 2007 1:04 am

by A. Square on Sun Dec 23, 2007 1:57 am

You might also want to try a 595 bitshift chip:


Chaining three 595s together to drive 24 LEDs is still less than half the price of one MAX7219/MAX7221 chip.
A. Square
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Joined: Mon Dec 17, 2007 12:51 pm

This should be adaptable to the 595

by mrmeval on Mon Dec 24, 2007 5:09 pm

Hi, New User here:

My LED circuit using a similar chip the HEF4794 by NXP

http://forum.sparkfun.com/viewtopic.php ... af9732fb70

Shiftout only does 8 bits, the HEF4794 will daisy chain the bits with two shift outs in a row without the command to transfer the bits to the outputs. The 595 has all that the HEF does except the LED driver though the datasheets on both are vague on current draw per pin.

My code is vile and will only do 16 currently, each additional chip adds 8 and will need another shiftout prior to the transfer to the output. It should be trivial to add more chips up to the limit of the digital outputs then you use an ic to boost the signal. Also not my code was for testing. It needs rewritten for what ever you'd want to do with it.

I have the 595 I've just not had a chance to modify the code and circuit.

I've seen where a 595 has been used as an interface to a parallel input LCD using three wires. I think the HEF4794 can do that as well.

My only gripe with the HEF4794 is that it's erratic till the arduino can kill the outputs. Not good if I want to control something other than LEDs.

I have hooked one of the outputs to a solid state relay and run a lamp, don't use CCFLs they commit suicide. I'd not want to do this until I find or make a reset circuit to force the chips off until the arduino comes up and takes over.

There were several DIP package chips with more than 8 outputs the two I know of are now obsolete.

The benefit of these types of devices is that any one output is fully on or off, there is no scanning needed. The MPU doesn't do a thing unless it needs to change the display.
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Please be positive and constructive with your questions and comments.