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I have a 5m strip of 24v tunable white LEDs and I'm trying to figure out what I need set it up. There's a pad for V+ and then one for brightness and one for warmth. If I plug the V+ in V+ on a 24v supply and the two others to V-, the whole thing lights up full intensity. The strip draws 16 Watts per meter (80 for the whole thing). As I understand it, you vary the two anodes by varying the resistance to ground. I've seen some instructions that this can be done with PWM pins, but I'm assuming that given the voltage and current, no arduino or similar can handle that much. Do I need transistors then? What specs do I look for to understand the limitations?

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    please post a link to the product datasheet – jsotola Dec 20 '19 at 22:47
  • I linked the product. It doesn't actually have a straightforward data sheet but it has all the specs. – jiggy Dec 21 '19 at 1:37
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    There's a pad for V+ and then one for brightness and one for warmth. ... that is not quite correct ... the pads are V+, W and C ... W controls the warm color LEDs and C controls the cold color LEDs ... you will need a transistor to drive each of the two channels ... find a tutorial about driving RGB LED strips ... instead of three colors, you have only two colors – jsotola Dec 21 '19 at 1:50
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Your strip has 2 LEDs with different color temperature directly besides at the same spot for every element of the strip. So the adjusting of the overall color temperature is done by changing the relative brightness of both LEDs. If the LED with the warmer light is brighter, the overall color temperature will also be warmer. Common Anode means, that V+ is the connected to the positive pin (anode) of both LEDs, so it has to be connected to +24V. The electrical circuit is completed by connecting the pins W and C (Warm and Cold) to ground. To control the individual brightness of the warm and cold LED groups, you have to use PWM.

You are right, that an Arduino cannot handle currents this big. You need a transistor for this. I would suggest using a MOSFET, since this is the easiest and most efficient possibility. By one MOSFET for every channel (Warm and Cold), which is capable of handling the needed power (Important! Or you will fry the MOSFET). Also it should be a logic level MOSFET, that is well in saturation of the gate voltage for the output voltage of your Arduino. Connect the MOSFETs Drain pin to the channel on the strip, the Source pin to ground of your power supply and the Gate pin to a PWM pin of the Arduino. Also connect the ground of the power supply with the ground of the Arduino.

Now you can control the brightness of the Warm and of the Cold LEDs by adjusting the PWM duty cycle with the Arduino.

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    Or rather, by adjusting the ratio of the duty cycles between the warm and cool LED sets. If you set the cool pin to 100% and the warm pin to 0%, you'll get all cool light (100:0) If you set both to 100%, you'll get a 50/50 mix of warm and cool light (ratio of 1:1 between duty cycles) – Duncan C Dec 21 '19 at 22:50
  • So, presumably if I tie warm straight to ground and just air gap cool, I'd get warm – jiggy Dec 22 '19 at 1:27
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    @jiggy Yes, thats correct – chrisl Dec 22 '19 at 10:26

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