I work on a DALI lighting system for home usage and I design all DALI devices from scratch. In this system, also a sensor module will be implemented. Since it will draw only a negligible current (app. 4 mA), I thought it would be convenient to use DALI interface itself to power this device. Commercial products usually offer this feature, but I couldn't find any details on how exactly does it work.
Just to clarify, DALI logic levels are 9.5 - 22.5 V for HIGH level and -4.5 - 4.5 V for LOW level.
So what I need is some basic idea or schematic of circuit I can use to turn DALI interface into some sort of power supply.