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Author Topic: [Mini Arduino Pro] Driving 12 RGB LEDS Questions  (Read 1971 times)
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Hi,
Im make a simple project, but i not sure what way to take.

The goal is to make a simple RGB Lamp.

These are the components:
- 3.7v rechargeable battery (3000 mah)
- 12 RGB LEDS (common cathode)
- Mini arduino Pro (3.3v/8Mhz)

The lamp will have 4 sides and for each side there are 3 RGB LEDS.

I dont need to decide the color of each LED. But i need to decide the color of each side (3 RGB).

That's all.

Now my questions:
The Mini arduino Pro have 3 PWM outputs, and each LED needs 60mah (20mah for each color).

I should put the LEDs of each side (3 Leds) in Series? But in this case i must provide 12 volts each side right?. If yes How? (i have 3.7volt battery)
Or can i put every led in parallel ?

The Mini Pro can provide all the necessary current?

To do this project what additional components i need to drive the leds??
Or can i do this project with these components that i have?

Thank you very much in advance.
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and each LED needs 60mah
No it doesn't it might need 60mA but not mA Hours.
 

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I should put the LEDs of each side (3 Leds) in Series?
You can't put common adode (or cathode for that matter LEDs ) in series.

Quote
Or can i put every led in parallel ?
No choice, yes. But each one will need it's own resistor.

Quote
The Mini Pro can provide all the necessary current?
No.
You will need a transistor to drive each colour.
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personally I would avoid connecting the leds in series, I would go for a parallel arrangement.

now with only 3 pwm's to control you may not have the level of control that you would wish for. you may want to look at investing in another board with more pwm's.  

as for your current board i would hook up all twelve leds together so when you turned on say output "blue" all sides of your lamp would light blue. What is this project for exactly? With more information I might be able to provide you with the answers you need.


and Now for the math.
if you look at the leds current draw 20MA per color, in parallel the three leds per side would have a current draw of 60ma. The mini pro can supply up to 40ma per channel so i would suggest using a simple NPN transistor to keep from frying your output pins.

im sure that others here have even better ideas on how you could accomplish this.

Hope this helps
Nicholai
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You have common cathode rgb's?

which pin is shared?
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@cjdelph

Yeah, the negative of the RGB LEDs is in common.

So i have these pins on each LED:

-Red
-Green
-Blue
-GND

@Grumpy_Mike

You are right, i can put the leds only in parallel.

So you are suggesting me to use each (3) PWM output for one color and put a transistor on each color line to guarantee the needed current, right?
With this solution i will not have any problem, but all sides will have the same color. Right?

nicholai414

The project is for a Simple Lamp. Really.
I can make it "one color version" too. But deciding the color of each side will be pretty awesome for some cool effect.
So, in your opinion i need 12 PWM Outputs (3 PWM x 4 Sides) to make the multi-side-color version?

Thank you all guys

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wow... do you have a link? i have over 100 common anode's ... Even though i asked for common cathode and bought common cathode! 3 lots different supplies they ALL keep sending common bloody anode!





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So no one can say to me how done this?

@cjdelphi
you can chek on spark fun or ebay.

https://www.sparkfun.com/products/9264
http://www.ebay.it/itm/25x-LED-klar-g-Minus-5mm-RGB-4-Pin-rot-grun-blau-rood-groen-blauw-10000-mcd-R-/150760360526
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So you are suggesting me to use each (3) PWM output for one color and put a transistor on each color line to guarantee the needed current, right?
With this solution i will not have any problem, but all sides will have the same color. Right?
Yes all the sides will be the same colour but with only three PWM outputs you don't have a choice unless you use some other chip to generate the PWM signal for you.

Other options are to go for LED drivers, I like the PCA9685 chip, that is I2C controlled and gives 16 PWM outputs so you need just the one chip to do what you want with a different colour on each side. It will drive up to 25mA per output.
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Yes all the sides will be the same colour but with only three PWM outputs you don't have a choice unless you use some other chip to generate the PWM signal for you.

Other options are to go for LED drivers, I like the PCA9685 chip, that is I2C controlled and gives 16 PWM outputs so you need just the one chip to do what you want with a different colour on each side. It will drive up to 25mA per output.

Woah, seem perfect this little chip.

Fast questions:
With this chip i need a resistor on each LED too?
if i will use 3 outputs of this chip to drive each R-G-B line of 2-3 RGB leds in parallel, in this case i will need a Transistor, right?

Thank you very much for your precious suggestions.

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@OP-

I think if you use this chip: PCA9685 chip..  you would not need to use the transistor(s) anymore...no?  As the driver chip woudl supply each 'output pin' with 25mA for that 'led'...

going this route (as mentioned) gives you the flexibility to make each wall a color of your choice.. where are transistors is limiting you to the same color for ALL walls..


« Last Edit: January 14, 2013, 08:40:32 pm by xl97 » Logged


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With this chip i need a resistor on each LED too?
Yes.
Quote
if i will use 3 outputs of this chip to drive each R-G-B line of 2-3 RGB leds in parallel, in this case i will need a Transistor, right?
Yes.

Xl97 - he said he has common cathode LEDs so unfortunately that is not the right way to wire those.
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yikes!..

I'll remove the images right away as to not confuse!..

(but correct for common 'annode' (+) leds)??



images update..(both RGB types posted)

thanks.

update: corrected/both images added*
« Last Edit: January 15, 2013, 11:27:37 am by xl97 » Logged


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Yes that would be right.  smiley
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ok..how about these..lol

common cathode:




common anode:


each 'row' of 3 x RGB leds is your 'wall'..
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Yes very nice. You just need to say that for the common cathode type you will need PNP transistors and NPN for common anode.

The transistor common line is always the emitter with the collector going off to the LEDs.
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