So use the 5V 1A switching regulator, will be a very stable 5V source for your 25mA plus the arduino's 30mA.Use the analog devices SPI ADC that's been posted previously with 6 sample & hold inputs & get 6 conversions at the same time.
Why not just get a switching 5V regulator? Then you won't see any variation.http://www.dipmicro.com/store/DCA-0510http://www.dipmicro.com/store/DCA-0520Or get 6V, 7.5V if you want to regulate it down yourself. Maybe use an LM317 with a trimming resistor (10 turn potentiometer) to get it right at 5v.
yes, but I'm using a precision 3.3v regulator as the external reference voltage for the Atmega328, so if the 5v excitation voltage varies, the output of the sensor compared to the stable 3.3v varies as well.