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First, I'm an Arduino noob although I am getting comfortable with many concepts.  I have excellent C programming skills but minimal electronics skills.  I need some help assessing a project.  My project is a lighting a small scale fake tree (24 inches tall) with between 25 and 30 LEDs that will be animated in a number of patterns (twinkling, chases, etc.) so independently controlling the LEDs is a must.

I would like to use RGB LEDs.  However, I could get by with bi-color LEDs.  I would prefer PWM the LEDs for fading effects if feasible. 

I guess one question is whether there are ways to independently control RGB LEDs with less than 3 pins per LED.  Such as pulsing the color information on three pins to multiple LEDs and control the cathode to light the correct LED (I'm thinking like how an interlaced computer display draws every other line).

Is there a shield that would allow me to control 25-30 RGB LEDs independently?

Any ideas would be helpful.   

Thanks!
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Standard 3-color LED has 4 pins, anode/3 cathode, or cathode/3 anode.
If you use a part like TLC5940, can have uC controlled PWM to 16 current sink LEDs simultaneoulsy, so anode/3cathode is preferred to keep parts count down.
25-30 LEDs = 75-90 outputs to control. /16 = 5 or 6 [edit ->] TLC5940s.

However, you say 'RGB LEDs with less than 3 pins per LED" - do you have a link to the part you have in mind?
« Last Edit: July 13, 2011, 12:12:07 pm by CrossRoads » Logged

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Crossroads, I think the OP is asking if there is a way to control them using less than 3 pins for each LED. My recommendation would be as many TLC5940s as needed, daisychained together.
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Correct Bilbo - I was hoping for way to be more efficient with less pins (via code) but it sounds like "as many TLC5940s as needed" is the best approach.  Or I was hoping for a pre-existing shield with that many PWM outputs.

Thanks for the input.
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If you're after a shield rather than soldering practice, there are lots of options for you.  iTead has an 8x8 matrix color shield that is reasonably priced that should be more than capable of driving your project (http://iteadstudio.com/store/index.php?main_page=product_info&cPath=18&products_id=312&zenid=g9r1efj1n3iqt5pct82qam11k0).  This shield will give you independent control for up to 64 individual RGB LEDs with PWM control.
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You might be interested to know you can now get RGB LEDs in strip form complete with driver chips that allow individual control via some sort of serial interface to every LED - not cheap, but then 32 RGB leds aren't that cheap anyway - looks interesting and might be
useful for this project:

http://www.sparkfun.com/products/10312
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You might be interested to know you can now get RGB LEDs in strip form complete with driver chips that allow individual control via some sort of serial interface to every LED - not cheap, but then 32 RGB leds aren't that cheap anyway - looks interesting and might be
useful for this project:

http://www.sparkfun.com/products/10312

And as a bonus, Sparkfun has supplied a example code! I am already getting this for light painting.
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If you're after a shield rather than soldering practice, there are lots of options for you.  iTead has an 8x8 matrix color shield that is reasonably priced that should be more than capable of driving your project (http://iteadstudio.com/store/index.php?main_page=product_info&cPath=18&products_id=312&zenid=g9r1efj1n3iqt5pct82qam11k0).  This shield will give you independent control for up to 64 individual RGB LEDs with PWM control.

That shield looks great but can you really independently control 64 RGB LEDs?  There doesn't seem to be enough pins!  Or is this some sort of multiplexing scheme that share color information between neighboring LEDs?  Keep in mind that I am not building a matrix or a cube.  The design would be 25-30 LEDs that appear to be randomly placed in a model tree (kinda like independent RGB lights on a little Christmas tree). 


 
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I would go 5 RGBs each on 5 TLC5940's then, using 15 of 16 pins.
5 1/3 if  you can keep track of one LED being spread over 2 parts.
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Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

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