Not battery powered any more!

I have always been a fan of the small Christmas lights that are battery powered, they usually have tiny LEDs run on very thin wires and don’t have any flicker or PWM drive because it’s powered from batteries. This year I picked up a few that were powered by two AA batteries and decided to decorate the living room to feel more festive despite the lack of company. My only issue is that I don’t care for using batteries, especially non rechargeable ones for something like this. So I decide to put a small DC to DC supply to use and enclose it in a project box.

Using a 35w 24v supply to power the DC to DC converter it is stepped down to ~3v for the LED lights. The strings can be either white light or colored light but not both at the same time. Since they are just two wires going to all of the LEDs I was wondering what controlled the color of the light. Using an oscilloscope I was able to make a very simple finding, the power to the LEDs is controlled by a 2 position switch that just changes the polarity of the output. The LEDs are all on the same bus with opposite polarity, simple and elegant.