What i'm thinking, after giving this some thought, is as follows-
Use the 9v input supply for the arduino to power a sepic converter to give me 12v dc cv to power the pwm dimmer. Take the up to 12v pwm out from the dimmer, and use this circuit to allow it to take the pwm 12v, and give a linear 0-5v out for the analog in-
The second optoisolator one.
The question i have, is regarding resistor values, or potiohmeter values for a (lets say 9v 1a ac/dc wallwart, or a current limited dc/dc sepic), to power the pwm dimmer and arduino with minimal power loss to heat in the resistors to limit the current draw from the ardiunos dc supply (9v 1a) that powers the 12v dimmer, and where to put them (IE before the sepic, inbetween the sepic/pwm dimmer, etc).
Since it needs very little current at the input of the pwm dimmer, but 12v regulated (where the sepic comes in handy, but i'd rather use resistors than a more expensive current limited sepic), whats the most effecient resistor values to use, and where in the circuit to put them to cause the sepic drawing from the arduino 9v input, to only pull 100ma max, but allow 12v cv to the dimmer? 100ma, derived from some effeciency loss at the converters, power for the rf pwm dimmer and 40ma as the usual current when using the 5v+ arduino pin for analog input applications.
IE, i want the dimmer circut to be current limited to ~100ma (give or take, i'd like to use a pot if thats too high/low after testing) when drawing from the 9v 1a dc source that powers the arduino. My thinking is without current limiting, i would be sinking all the supplys amps into the dimmer/optoisolator 5-12v -> 0-5v circuit, when only 100ma max is necessary, to power the rf pwm dimmer, effeciency loss at the sepic, and the 40ma for the 0-5v to the arduino. Since this is something that may be drawing from backup lead acids at some time, i'd rather it use as little wattage as possible for the pwm/optoisolator 12v to 5v conversion, and theres no point wasting power anyway, regardless of a ac/dc source, or dc battery source. I just want it to be as effecient as possible.
Basically, what resistor values/pot values and where to put them in the described circuit is what i need help with. I can draw up a complete circuit diagram including the sepic and pwm dimmer if that makes my question easier to understand, just let me know.