Electronics at the end of standard incandescent dimmer circuits

[westfw]

Suppose that I want to replace an incandescent lamp on a standard triad-based dimmer circuit with some electronics.
Say I want an LED circuit that changes the number of LEDs illuminated, or their color (RGB LEDs) with the setting, rather than just the power…
As I see it, I’d need at least two “interesting” bits in my device:

1) I need a regulated (and hopefully isolated) DC power supply that works on the nasty waveform put out by the dimmer.  I guess something that rectifies the AC before anything else would be a good start, but it still seems that it would have to handle quite a large variation in input voltage.  Are their standard circuits for this?   OTS modules?  (Maybe an “LED Ballast”?)  It needs to provide 5V at maybe 10W-20 or so...
2) I need a circuit (or more likely, firmware) that can detect the setting of the dimmer, either by measuring the intervals in the raw AC waveform, or perhaps by measuring the power supply input voltage after rectification.

These both seem like they ought to be “solved problems”, so I thought I’d poll the community for ideas before I go off and try to invent the wheel…

[David Hess]

Dimmable ballasts designed to work with phase control dimming measure the average input voltage to detect the dimmer setting.  Of course they are also designed to operate over a wider input voltage range.

Incidentally, I tested some Cree dimmable LED lamps a couple weeks ago and found that they worked fine being dimmed by a variac instead of a phase controller dimmer.  This might be an option for those who want dimming without all of the noise from phase control.