I would just power the Arduino using the external power supply, connected to the 5V Arduino output.AREF must not exceed the Arduino power supply voltage, which easily possible if, for example, the Arduino is powered by the USB bus.
Is that correct?
Just don't use Vin pin for powering both (arduino and analog circuit)
Ratiometric sensors are generally best measured by not using AREF, but just using Vcc as reference. Especially if that's the same voltage that powers the sensor itself (you're not clear about that part, or what the sensor even is).
I was hoping that, by tying AREF to the same source that powers the sensors, I could get rid of this issue (because the reference and sensor output would then both be influenced by any shifts in supply voltage).
The SFH 9206 draws most of the current.
According to the processor data sheet, the analog input voltage should not exceed Vcc.
And that would be four times 20mA?I think you're creating more problems than you have.You should be able to draw several hundred milliamps from the Micro when on USB supply.Leo..
... The same accounts for the sensor outputs which may destroy your analog inputs. ...