Introduction: Dimmable LED Stair Lights
Here are some pictures of a set of LED stair lights I made for our house. They are dimmable, with a switch at the top and bottom of the stairs to turn them on and off. The main control box with the dimmer is at the bottom of the stairs.
The bit I was pleased with was working out a circuit that lets you use the same pair of cables for the LED power and for the switch signal from the top box. By the time I decided I wanted both switches, I'd already soldered the LEDs (plus resistors) into a two core piece of mains flex, so getting the switch signal back down the cable to the main box took a bit of thought. In the end I found a way of shorting the power very briefly through a capacitor, and detecting the current pulse using a comparator. The signal from this goes to a toggle flipflop, which switches the power on and off.
The dimmer circuit is comparatively simple - basically just an adjustable current source using an opamp and transistor.
Hope you like the pictures. I may get round to putting up a full instructable if there's interest.
Update: I've just added a couple of photos of the original hand-drawn circuit diagram, and of the notes I wrote to work things out.