LED wiring question

I have a cabin light that has both white and red LED's. The light shares a common ground. It has a white lead for the white light, a red lead for the red light and a black lead for the ground.

I would like to be able to switch the white light on and off with it's own switch, and be able to dim the red light with Dynon skyview. The problem, I think, is the common ground.

How do I share the ground and maintain the proper polarity that the dimmer needs?

I don't see a problem, but I don't fully understand your dimmer requirements. The common ground is connected to ground. The white wire is switched to +Vbattery and the red wire is connected to the dimmer output. The dimmer ouptut will go from ground up to +Vbattery.

Now the problem may be your dimmer. For an LED to be dimmed properly usually a PWM signal is used. This is a repeating variable width pulse. The wider the pulse the brighter the light. Its based upon duty cycle. 100% on is brightest, 0% on is off. An LED requires a small voltage to turn on so typically you can't just vary the voltage like you could with an incandescent bulb. It can be done but its a little trickier to do properly.

Yup, you need a simple on/off switch for the white positive power lead, and a PWM dimmer control for the red positive power lead, and simply tie the black lead to ground.

The SkyView dimmer PWM supplies the negative side of the LED circuit. A DPDT switch could be used. One half of the switch will control which LED gets positive voltage. The other half of the switch will connect the black wire to either ground or to the SkyView dimmer output. Did the cabin light come with any documentation?

I think the problem is that the Skyview DIM output is open-collector, meaning it switches ground and not power. So, you can't directly use the Skyview to dim the red without dimming the white also. To make matters worse, most dimmers work that way -- it's a lot easier to switch the ground than the supply side.

For a single LED, you could simply use a potentiometer on the power to the red LED. You really don't need a fancy PWM dimmer for a low current load like one or two LEDs. Of course, that's a separate knob. If you really want to do it with the Skyview, I like the DPDT switch idea, with a center OFF position.

Bi color LED circuit

Dimmer Issues

Thanks for all the suggestions.

Here is a more detailed explanation of what I am trying to do.

I want to be able to turn on the white portion of the light without turning on the master switch, I have run a lead from the battery to the switch. The red portion I have hooked to the master bus and a Kick PWM dimmer. The dimmer needs both the positive and the ground run through it.

My thought is that I would use the white light, without turning on the master, for loading the plane in the dark. And use the red light during flight and have it dimmed by the Skyview PWM dimmer.

So far everything I've tried won't work. I have issues with the red being dimmed along with the white as Dale said.

I will try the DPDT switch idea.

Schematic

Thanks for the schematic Joe, it worked out perfectly!

You are welcome.
Jim Weir designed a circuit that he published in the July 2014 issue of Kitplanes.
This circuit keeps the interior light on for a period of time after the master switch is shut off.
It is similar to the dome light in cars that stays on for awhile after the car door is shut.
Kitplanes subscribers can download the article HERE.
Here is the updated SCHEMATIC. (available to everyone)
The light will always be on when the master switch is on AND S1 is on. When the master is shut off,
the light will remain on for a period of time determined by the value of C101.
The "Keep Alive" power comes directly from the fused battery bus.

Just to update for anyone else looking for such a design: the link to the schematic that Joe posted no longer works, but I was able to find the document at a similar link:

http://www.rstengineering.com/kitplanes/KP2014/KPsch%20RevB.pdf