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Author Topic: Multiple LED drivers power problem  (Read 488 times)
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I'm pretty new to the Arduino and designing circuits.  I'm hoping someone can help me out with a project I'm working on.
I have a Duemilanove board and I am using 3 daisy chained 4794 LED drivers for 24 LEDs.  I have the circuit set up and the code working as it should, everything lights up and does exactly what I want.  
My problem is that the 8 LEDs on the first 4794 are brighter than the LEDs on the other 2 drivers.  I have the same resistors on each LED.  I'm pretty sure there's not enough current on the Arduino to power all of these LEDs, but why are the first 8 bright and the remaining 16 not?  I would think that they would all be dim.  I have the Arduino powered with a 9V .66A adapter and have tried using the Vin pin to provide power for the LEDs, but it didn't change anything.
I would appreciate any advice for brightening the remaining LEDs.  It would be great if I could power both the Arduino and the LEDs with one power source.  Thanks!  

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Just a starting point, but make sure all the 4794s have good power and ground.  Chips #2 and #3 might be getting power or ground from the daisy chain, not from the board.  If the board wasnt providing enough current, then should all be dim.
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Thanks for the reply, I was thinking it had something to do with daisy chaining power, but I have power and ground on each chip coming from the +5V and ground rails of the breadboard.  I also have the LED anodes going to the +5V rail.
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Try some decoupling, there might be some oscillation of the other chips making the LEDs look dim. Foe an introduction to decoupling see this:-
http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html
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