16LED (single color) strips with ULN2003A control

[richCarthew]

Hi All,

I'm planning an artwork that uses the Arduino (Duemilanove ATMega328) to control its LED lighting in six areas. I can do this easily with standard single LED's, however this one is going to need much more light ...

So I've been working through Google & the forum to see how I might control some LED strips perfect for the task (each +12v, ~250mA) from the Arduino PWM pins via the ULN2003A Array.

I have a reasonable idea of how the sketch will look and 90% of the concept & information etc wrt the Darlington Array.

Where I'm stuck is with the schematic - specifically how to connect these particular LED strips. Heres' the LEDs datasheet http://www.hebeiltd.com.cn/led.strip/STR2-16R-40.pdf The below schematic is similar & is from an earlier post by Makkan (thanks):



http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1236091181

It looks close, but the LED strips I have provide only a +ve and a -ve connection, so this is where my limited experience in circuits and electronics has left me hanging  

1. My final goal is to use the Arduino to control each fade routine independently on six of these LED strips at the same time.
2. Power supply: The strips can be daisy chained together to run off the same 12vdc transformer as long as the amperage
is sufficient, but my gut tells me maybe not in this case, due to wanting them to fade independently? If it were possible to safely power the Arduino and all six boards from one source, that would be a huge bonus!

Any help much appreciated and will be acknowledged  
Many thanks!

Rich.

[Grumpy_Mike]

It looks close, but the LED strips I have provide only a +ve and a -ve connection,

This is because they are only one colour and not RGB.
So go with that schematic and where it says R pin on RGB strip connect it to the -ve on your strip.
Do this for other strips for the G pin and the b pin on the schematic.

Just don't overload the 2003 as despite it having a current rating that is good it also has a power rating, so this limits what you can switchsee:-
http://www.thebox.myzen.co.uk/Tutorial/Power.html
and
http://
http://www.thebox.myzen.co.uk/Tutorial/Power_Examples.html

[richCarthew]

Hi Grumpy_Mike,

Many thanks for your prompt response  

I appreciated the link to your tutorials (nice reference to absolute zero!) - I have a much clearer understanding of the relationship of power vs current rating on this IC (& for future work too) - I fully recommend these toots to others who are new to this as well.

The LED strips typically draw ~ 250-300 mA each @12Vdc, so following your lead, I would use a max of two per 2003, leaving a safe margin of about 100 mA+

The below schematic is where I'm at now with one 2003, and requires completing.
I could try and connect (on the strips) the indicated points 1 -> 5 & 2 -> 6, but this would be a guess at best, and maybe burn something. [edit - I'm having trouble including the img sorry, could you check out the link-thanks]
http://richcarthew.com/images/uln2003_post.html

Hope I'm on the right track here as I know my circuit theory is rough. I can do the math fine, but my experience in circuits, well...

Thanks again for helping me along the way,

Rich.

[Ran Talbott]

Instead of using a ULN2003 for each pair of LEDs,  you might want to use "logic-level" FETs.  They'll be similar in cost and complexity of wiring,  with less heat to dissipate if you pick FETs with a low R_DS(on).

[richCarthew]

Hi there Ran,

Good idea with the FETs, thanks!
I had seen a reference to them in Grumpy_Mike's power tutorial too and plan to check out something like the IRL520 later, once I got this circuit working..  datasheet: http://www.hobbyengineering.com/specs/IR-irl520.pdf

Speaking of the

complexity of wiring

this is my problem, as I've yet to successfully run these LED strips

Any advice on my current (no pun intended!) schematic to get them glowing also welcome!
Link: http://richcarthew.com/images/uln2003_post.html

Many thanks,
Rich

[Grumpy_Mike]

Circuit looks OK, apart from the missing +12 connection to the second strip.

[richCarthew]

Excellent! they are working well, Thanks Grumpy_Mike & Ran!

The 2003 remained cool with two LED strips running for 60 mins (due in part to the duty cycle from the sketch keeping the average power low, I guess). I tried three linked to the 2003 also with moderate temp, well under 40degC to the touch.

Thanks Grumpy_Mike & Ran for persevering.
Next step is make the circuit and artwork.

This'll take about two months and involves 18th Century anatomic artwork. Will acknowledge your help and send you a link if interested?
Let me know.


Cheers,

Rich

[richCarthew]

Hi All,
For anyone who has been following this and is interested in the completed circuit using the ULN2003, check:

http://richcarthew.com/images/uln2003_post_final.html

The 12vdc supply I was using had a current rating of 100 mA [I don't think the transformer was regulated] and drove these two boards fine. After touch testing the temperature over 30 mins of operation, I added another LED strip into the circuit off the same power with no problems.
From what I understand in Grumpy_Mike's tutorials, if the LEDs were on constantly, the 2003 would probably get hotter when running three strips. Then go with the FETs as Ran suggests.
R

[Ran Talbott]

This'll take about two months involves 18th Century anatomic artwork

You definitely need to post pics and links in "Exhibition" when it's done.

[richCarthew]

Sure thing Ran!
Cheers,

Rich