flashlight

Reading a voltage would be possible (but the ADC code is already very complex and messy). Some types of drivers have a sense resistor already, but usually it is connected to an opamp and adding another load might cause visible fluctuations in the output.

So yes, it could be possible, but requires a driver redesign and lots of refactoring of Anduril.

While I agree that this would certainly be interesting I don't really know how this could work. First of all: Real current sensing can only really be done with a constant current driver. Not saying that this would be accurate but this should indeed work for an estimation. But now the first problem arises: Most CC drivers also include a FET for turbo and/or the higher range of the ramp. The moment this switches on you're out of luck. Another option would be to add a sense resistor. This - again - would surely work to measure current. But you now have the problem that you introduce an (unnessisary) resistance in the driver, limiting the output of the flashlight (if it includes a FET). And lastly I just think that while it surely sounds like a cool feature it's just not something most flashlight enthusiasts would use regularly. Altering the flashlight circuit for a feature some people may use once or twice out of curiosity with a given flashlight does not seem reasonable and ToyKeeper IIRC has many things on her to do list that she wants to implement. Since this is such a nieche feature that (for what I know) would need hardware modifications on many flashlights out there, I don't think that this will get implemented.