# Bi-color LED Intensity + Color Control

Full transparency, I'm a cinematographer, not an engineer, so forgive my ignorance here!

I'm attempting to make an inline dimmer for small bi-color LED strips and fixtures. I have larger, more expensive controllers for larger more permanent fixtures, but for the flexibility and weight I'm trying to achieve with these smaller accent lights, I want lightweight and simple.

So far, I have had limited success with two high speed (10khz) PWM dimmers that I've wired in succession to control the two channels on the strip individually. However, when it comes to precision control of the color temperature achieved by the on-off-blended nature of the two LED colors, this is less than ideal. What I would like to design is a very simple controller with two knobs:

1 for brightness/intensity. 1 for color control (transition from 2800K to 6000K).

This is beyond my awareness to achieve simply because I don't have the vocabulary of components to design something like this. Any help and thoughts would be greatly appreciated!

The LED strips are these

The PWM dimmers are used in the first version are these

• In general, link shorteners are frowned upon, because they hide the actual destination of the URL. You can use Markdown's URL syntax ([text to show](http://where.to.go/)) to make the links look shorter, without hiding their destination.
– Nic
Dec 26 '16 at 17:15
• For cinematography, you may want to look a bit deeper at the colour rendition of LED lights. Some interesting info from @ariser in these Q&As... electronics.stackexchange.com/questions/203264/… and electronics.stackexchange.com/questions/204998/… Dec 26 '16 at 17:42
• If you want finer, automated control then you should consider using a microcontroller in combination with a couple of potentiometers and low-side MOSFETs. Dec 26 '16 at 18:34

Figure 1. The CIE colourspace with a "best-fit" line running through the whites.

To do what you want would require some good fortune with availability of the right LEDs. To be able to adjust along a best-fit spectrum of whites requires that you have two light sources with colours on the outer ends of the line overlaid on the graphic of Figure 1. Colour control in this case would be fairly simple: blend between blue only to gold only.

If the colours don't line up as desired then you would need at least three colours.

Figure 2. With three colours (located at the points of the triangle) any colour within the triangle can be generated.

In this case control becomes a little more complicated but could still be done without resort to a micro-controller.

Figure 3. A green-blue pair and a green-red pair could generate the two colours at the ends of the grey line.

If a green-blue set of lights is adjusted to generate the blue at the left end of the grey line and a green-red pair is adjusted to provide the hue at the right end of the line then, by varying the relative intensity of the pairs we could travel in a straight line through daylight, cool white and warm white.

Update

simulate this circuit – Schematic created using CircuitLab

Figure 4. A very simple 0 - 10 V dimmer control.

How it works:

• This control is designed to work with 0 - 10 V LED controllers.
• It uses two 2-gang linear potentiometers (pots).
• R1 controls the intensity. As the potentiometer is turned from minimum to maximum the wipers' voltage will increase from 0 to 10 V.
• R2 controls the temperature. Note that the potentiometers' inputs and grounds are reversed. When turned all the way to the left the cool control will get the full value of the intensity setting while the warm control will be grounded and get zero volts. When turned all the way to the right the situation will be reversed.
• With R2 in the centre position both lights will be at 50% intensity. This is intended design to maintain intensity across the range of the temperature control pot.
• The 1 kΩ and 10 kΩ values are chosen so that R2 doesn't load R1 too much (as this would distort the desired linear adjustment.

Figure 5. The potentiometer connections on the PWM controller are not grounded.

Unfortunately your Amazon controller is not suitable for this scheme as the pots have neither end (points 1 and 3) grounded (to 4) and so must not be using a control voltage as required.

Many LED controllers are available with 0 - 10 V control inputs. While it may not suit your application, my article Dimmable mains PSU control explains some of the control features.

• Thanks for responding. However, I was not looking for information on color rendition. If one were to follow the link to the LED product I already own, one would have seen information about the strips I own which are bi-color only. I've made my choice of LED strip already. So, now that we've gotten that out of the way, can anyone actually address the question, which, simply is: How can I actually make a controller that controls color temperature and intensity independently? Feb 7 '18 at 2:46
• You're a slow correspondent! See the update. Both your title and your post mention 'color' so I addressed that in my original answer. Your LED link is dead. This is one of the reasons we ask that the question contains enough information to stand on its own. The other is that we won't follow the links unless we feel we need to. Feb 7 '18 at 19:38