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Author Topic: RGB strip and ULN2003  (Read 7338 times)
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This is what i have build, and all is working great.
You can control the ledstrips with the shiftpwm library to control brightness and colors with PWM


* ledstrip-2.pdf (39.38 KB - downloaded 49 times.)
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but what happens to PIN 9?
Nothing leave it disconnected.

This pin is designed to be used with motors that generate a back EMF, by connecting this to the +ve supply will put a reverse diode across the load. You do not have to connect it to anything.
I think I understand it now, just a quick check to make sure I'll be doing it right:


Now when I look at this scheme, I find it a bit useless indeed to use there transistors to controll one single channel. What is your advice, replacing them with 3 BD679?
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Well you still have pin 9 connected.
Yes a single power Darlington would be good, but a logic level FET would be better as you will loose less voltage across it. See what your local supplier has in terms of logic level FETs.
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I made some RGB+white LED eyes for the house for halloween.. I would recommend using discrete transistors rather than the ULN arrays because you are going to be able to sink a lot more current with discrete power transistors. I would suggest TIP120, they are Darlington NPN and can handle quite a lot of current.  For an LED project I am working on at the moment, I am using home made darlington pairs, using 2n2222 for the control transistor and TIP41c for the power transistor.  Only draws a couple milliamps for switching and can sink up to 6A.

Is there current limiting built into the strips you bought?
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When the testing is complete there will be... cake.

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Well you still have pin 9 connected.
I did solder it all up and it works perfectly fine to control the LED strip using Arduino, thanks!
What would I need to adjust the brightness of this strip?

Do things like a PWM powered resitor exist, or would another ULN2003 on the 12V do the job?
« Last Edit: April 19, 2012, 03:35:20 am by PaulE » Logged

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Do things like a PWM powered resitor exist,
No.
Just feed the ULN2003s with PWM outputs, in place of what you have and use analogWrite to set the brightness
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do I have to connect each of the 2-8 PINs on the ULN2003 to GND
Yes otherwise there is no path to ground for the current, nor common reference for the transistors.

That circuit will work, providing your strip works by grounding the R, G & B signals. But it is a bit of a waste using three arrays only to use one transistor per array.

And what if my strip has one ground pin and each color pin requires 12v signal?
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Then you can't use a ULN2003 to drive it.
Look for a high sided driver.
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So wich would be best to drive 5m strip (pretty much the same as op's)? Is UDN2981 what I'm looking for?
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So wich would be best to drive 5m strip (pretty much the same as op's)? Is UDN2981 what I'm looking for?
Yes that should do.
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