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Author Topic: More mA for RGB led disk  (Read 555 times)
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Hi all,

I've just started playing around with the Arduino Uno. One of the the items I purchased was a 7 LED RGB disk which can use up to 420 mA on 5V. For starters I hooked the 3 RGB pins to ports 9,10 and 11 and connected the GND and started to mix some colors. Sofar no problem.

The pins of the Arduino only can deliver 40mA tough (so 3 times so 120 mA total) and I wish to brighten the LED disk, but I still want to be able to manage the colors.


The example / explanation of the following pages/topics are clear to me but I'm unsure how to translate this to my situation.
http://rcarduino.blogspot.com/2012/04/servo-problems-with-arduino-part-1.html
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1207112415


Can anyone point me in a good direction explaining how I could realise more vA's for my current setup and future analog driven projects?

Regards,

Henk
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Hi,

Nice to see you found my link. To pass more current to your LEDs, you can use individual transistors or a chip which provides six or eight transistors in a single package.

The way this approach works is that the transistor is connected in the current path of each led on the separate power circuit. an Arduino output pin is connected to the base of the transistor. When the arduino pin is low, the transistor will act like a switch in the off position. If the Arduino pin is high the transistor will act as if it is a switch in the on position. This switching between on and off works fast enough for the PWM/analogWrite that you are currently using for brightness and colour mixing.

If you search for 'transistor as a switch' you will find approaches using individual transistors, if you search for 'darlington driver' 'hex driver' or 'transistor array' you will find approaches using chips.

Duane B

rcarduino.blogspot.com
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Thanks for the explanation Duane. I will dig into it when I'm ready to build my LED lamp besides prototyping it.

I had a misunderstanding for digital/analog pins if I'm understanding correctly. As I understand now an analog pin is not much more than a pulsing digital pin. In my LED case with an analog pin I don't have to create the pulses which I should do with a digital one...
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Correct.  However, stop connecting that LED array directly, you will burn out the 328.  Those LEDs will draw as much as they can until their capacity, more than enough to destroy the UNO.

I am currently building an LED strobe, and have changed over to MOSFET transistors due to heavy current needs.. But with a max of 420ma draw, you can easily use ULN2003, which is a darlington array on a chip.. Seven digital switches essentially.  Hook directly to uno, and it can switch up to a total of 500ma.  They cost about twenty five cents.  It basically allows the arduino to switch a much heavier load than a pin can deliver.. In fact, it uses entirely different power source usually.  Most of my power LED arrays run at 12v, switched by a transistor controlled by the 5v at microamps required to operate a darlington switching pair. It all boils down to the same thing.. Using the arduino to do the thinking, not the heavy lifting...
« Last Edit: April 16, 2012, 04:28:46 pm by focalist » Logged

When the testing is complete there will be... cake.

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