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Topic: Multiple LED drivers power problem (Read 530 times) previous topic - next topic

Moeman

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!  


drspectro

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.

Moeman

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.

Grumpy_Mike

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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