RGB strip and ULN2003

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.

Grumpy_Mike:

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.

Might be a waste, but if it works it works :wink: These transistors aren't that expensive so I'm all fine with that.

I updated the scheme, you say it should work using the following?

What would happen if I put an analogWrite of 60 on the GREEN-PIN and 160 on the BLUE-PIN, would this create nice blue-ish color a bright Aqua-blue color (Asuming that the transistor doesn't work as a resistor)

If you are going to do that then you might as well parallel those unused outputs to spread the load. That is wire pins 10 to 16 on each chip together. The data sheet says it is fine to do this.

would this create nice blue-ish color a bright Aqua-blue color

Yes.

Grumpy_Mike:
If you are going to do that then you might as well parallel those unused outputs to spread the load. That is wire pins 10 to 16 on each chip together. The data sheet says it is fine to do this.

would this create nice blue-ish color a bright Aqua-blue color

Yes.

I see I missed a word there, what I meant was: "would this create nice blue-ish color or a bright Aqua-blue color?" :wink:

And what do you mean by paralleling the unused outputs on each chip together, 16 is the output I'm using to PWM each color, right? Or do you mean 9-15?

No I mean on each chip connect 15 to 10 together, and also the inputs 1 to 7 together. This makes the current flow through all the transistors for each colour, and so puts less load on the chip.

would this create nice blue-ish color a bright Aqua-blue color
Hey I am a bloke, only girls use names like that for colours, I don't know what you would call it, try it and see. :wink:

Grumpy_Mike:
would this create nice blue-ish color a bright Aqua-blue color
Hey I am a bloke, only girls use names like that for colours, I don't know what you would call it, try it and see. :wink:

Haha, what I basicly meant is if I will be able to mix different levels of blue by using an analogWrite or if it will always be the same blue, no matter what value I put in there.

Grumpy_Mike:
No I mean on each chip connect 15 to 10 together, and also the inputs 1 to 7 together. This makes the current flow through all the transistors for each colour, and so puts less load on the chip.

Can you give me an example of that, because I got really confused now. Do you mean something like this?

will be able to mix different levels of blue by using an analogWrite

Yes the intensity of the colour will change with the PWM value you feed it. By mixing different values you will get different colours.
For an example of this see the last half of the video in my project:-
http://www.thebox.myzen.co.uk/Hardware/Hexome.html

Take that last circuit. Remove all the black wires that go to ground.
Connect pins 1 to 7 together. Do this for all three chips.
Connect pins 16 to 10 together. Do this for all three chips.

Then wire pin 8 of all chips to ground. Do not connect pin 7 to anything.

Grumpy_Mike:

will be able to mix different levels of blue by using an analogWrite

Yes the intensity of the colour will change with the PWM value you feed it. By mixing different values you will get different colours.
For an example of this see the last half of the video in my project:-
Hexome

Take that last circuit. Remove all the black wires that go to ground.
Connect pins 1 to 7 together. Do this for all three chips.
Connect pins 16 to 10 together. Do this for all three chips.

Then wire pin 8 of all chips to ground. Do not connect pin 7 to anything.

Ok, so 1-7 are all connected to the Arduino PIN, the 8th goes to GND, 10-16 to the RGB-PIN, but what happens to PIN 9?

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.

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 (39.4 KB)

Grumpy_Mike:

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?

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.

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?

Grumpy_Mike:
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?

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

Grumpy_Mike:

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?

Then you can't use a ULN2003 to drive it.
Look for a high sided driver.

So wich would be best to drive 5m strip (pretty much the same as op's)? Is UDN2981 what I'm looking for?

cooba89:
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.

Can someone link or attach circuit for standard connection with uln and 12v led strip. Which works. Thanks