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[Reply #15 on:]

Hi,

Up,

I would like to use this schema with my arduino. I may receive soon the dx strip and an ULN2003.

I wonder how I can use an alimentation I found 12v / 1.2 A.

Can I plug it to the arduino and take the +12V somewhere on the board or should I use it exclusively for the strip with resistors to drop the current from 1.2A to 500mA ?

But maybe In this montage, the ULN2003 should receive 5V and not 12V ?

[Reply #16 on:]

Hi Franxoois,
The short answer would be yes you can, but you shouldn't.

I asked the same question a while back and someone with alot more experience in electronics gave me a good explanation of the reason why I shouldn't do it that way.

Instead I connected my +12V power source with one plug to the arduino and another to the led strip. Just don't forget that the circuit must share ground, otherwise it just won't work.

                +--- LED Strip ----+
Power -----|                          |----- Ground
                +--- Arduino ------+


Also I think you might have it backwards a bit. A 12V / 1.2 A dc power source does not shoot out 1.2 Amps it's probably the maximum rating for the power source.
Don't take my word for this as my knowledge of electronics is quite limited.

Good luck!

[Reply #17 on:]

Thank you for your answer. So we shouldn't but it works

If I understood well, the Vin on the arduino is directly connected to the power plug. So I could connect my power source to the arduino and take the +12V of the LED on the Vin socket ?

[Reply #18 on:]

Yes you could, but you shouldn't. The problem is, if I recall correctly, that the Arduino might not be able to handle the current needed by the LED-strip.

However you can connect the arduino to the same power source as the LED-strip as I described previously.

[Reply #19 on:]

Everything is ok.

Now, I would like to add a 3W LED star from http://www.dealextreme.com/details.dx/sku.4530 on the other pin of the ULN2003.

That led handle 2.9V AND 3.2V and 350mA. How can I drop the 12V to 3V ? What can I use, only resistors ?

I tried to apply U=RI, I found for the resitor 12-2.9 / 0.35 = 27 Ohm that looks strangely low ...  

[Reply #20 on:]

I think I'll have leave that to someone else. I haven't really had the time to fiddle with electronics since the birth of my daughter in late december so I'm way to rusty to even start thinking about that.

Good luck!

[Reply #21 on:]

Hi you all,

I borrow this same thread so the info will stay in one common place.

I'm also gonna light up my dx strips with ULN2003. I was just wondering can I simply connect Arduinos pwm:s to ULN's pins 1...7?
I started to hesitate since I saw this schema
http://amblone.com/guide (scroll down a little bit)
In that example the transistors are feed thru 2200ohm resistors.

Are any resistors needed with the setting with Arduino, ULN2003 and dx LED strips?

And are those dx strips common anode or common cathode?

(I understood strips have internal current limiting resistors)