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Multi-coloured LED strip?

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Hippogriff

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I was thinking whether I could create a poor man's multi-coloured LED strip by using several 10cm lengths of my RGB LED strip and then in-between each segment, wiring the colours wrongly, i.e. keeping 12v the same on all, of course, but at the end of the first 10cm segment, wiring R to G, G to R and B to B, then at the end of the second, wiring R to B, G to G and B to R, then at the end of the third 10cm segment, wiring R to R, G to B and B to G...

Then, if I told my micro-controller to send Red to the LED strip, would I get a Red 10cm segment, followed by a Green 10cm segment, then a Blue and then a Red, likewise, doing the same with the other colours - and getting some really interesting stuff when doing things like Orange etc.?

Would that work fine 'cos each LED has its own resistor in place, or would I still risk doing something bad to the pieces of RGB LED strip?

 

vne147

Member
I've worked with these LED strips a little before. Is that one from 3M? Each LED on the strip does have it's own current limiting resistor so you don't have to worry about frying the LEDs as long as you don't apply more than 12V to the '+' connection. If it's like the ones I've used in the past (and it looks like it is), they were common anode and you grounded the connection that corresponded to the color you wanted to turn on. For example, if you ground the 'G', green would come on, 'B' and it would be blue, etc. The different color combinations can be made by using your micro's PWM module if its got one. But, if you only light one color on a strip at a time, using PWM will only vary the intensity of that one color.

What your asking I think it can you use one output from your micro to turn on different colors on different segments and the answer is yes. Which ever connection you connect to your micro, that color will turn on. So it can be green on one segment, or blue on another, etc. The only kicker is that the segments can't be connected. They'll have to be cut.

Also, I'm not sure what you were planing but you should have the micro turn on a transistor to ground the segments. Don't sink that much current through the micro.
 
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Hippogriff

Member
Hi - thanks for trying, but I must not have explained my query properly.

I've used these RGB LED strips an awful lot - with transistors, Darlington Array ICs, with a variety of PICs - just high and low as well as PWM. I'm pretty au fait with what I'd class as 'normal operation'...

Obviously these things can be cut every 10cm - with 3 LEDs on each 10cm piece. You could then re-join them with bits of wire and get your 20cm or so back, with 6 LEDs. My question is about whether I can 'divert' the colour I want lit on each strip...

So, a 20cm strip would be like:

+---LED---LED---LED---LED---LED---LED
R---LED---LED---LED---LED---LED---LED
G---LED---LED---LED---LED---LED---LED
B---LED---LED---LED---LED---LED---LED

Two 10cm strips connected together would be like:

+---LED---LED---LED---Connecting Wire---LED---LED---LED
R---LED---LED---LED---Connecting Wire---LED---LED---LED
G---LED---LED---LED---Connecting Wire---LED---LED---LED
B---LED---LED---LED---Connecting Wire---LED---LED---LED

I have done this before on a 15 LED mood lamp - 5 x 10cm strips - but always keeping the connections going to the correct colours... the end of one 10cm strip red goes to the beginning of the next 10cm strip red etc..

What I'm thinking of doing is crossing over the wires between the two segments, kinda like this:

+---LED---LED---LED---Connecting Wire---LED---LED---LED
R---LED---LED---LED---Connecting Wire-\/LED---LED---LED
G---LED---LED---LED---Connecting Wire-/\LED---LED---LED
B---LED---LED---LED---Connecting Wire---LED---LED---LED

So that if I told my micro-controller to light up the red LEDs, it would do that on the first strip, and then the green LEDs on the second strip.

I guess I could just try it... I have a fair chunk of this stuff hanging around. I really just wanted to know if there was a theory reason as to why I shouldn't do it... but simply trying it out might be my best bet.
 

vne147

Member
My question is about whether I can 'divert' the colour I want lit on each strip...
Yes you can. You can connect R on one strip to G on another and then both to the same I/O pin of your micro. When your micro turns on that pin, red will turn on in the first strip, green in the second, etc. The 'R' connection on the strip is simply a bus connecting the cathodes of the three red LEDs together, the 'G' the the green cathodes, etc. It doesn't matter if the cathodes of different color LEDs are connected or not.
 

Hippogriff

Member
Excellent - this, then, is what I'm going to try for a piece of 'art' that I'm working on. Instead of 3 x 30cm LED strips (controlled by 9 pins) doing loads of different colours, I will do 9 x 10cm LED strips with 'detours' along the way doing many more different colours and still with 9 pins.

I just wish I could find that elusive x9 Darlington Array IC now... but I don't think it exists. I will have to stick with my ULN2003ANs (2 of) which will be overkill. Or I could drop down to 6 pins and have 6 x 10cm LED strips doing their stuff.

Thanks!

Edit: Confirmed this works like a charm - connected 3 10cm LED strips together 'incorrectly', by wiring red to green and then green to blue - then, when I send "red" from the IC, I get 10cm of red, 10cm of green and 10cm of blue. Likewise, different stuff if I send different colours - but if I send white, then I still get white, i.e. all on. Nice.
 
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