spandit:
Fair point! The node (where we're measuring Vo) is the input to a Megasquirt EFI controller which normally measures the voltage across a potential divider (between the 2490Ohm resistor and a thermistor). I'm giving it a voltage feed from an Arduino instead (the software is taking the average of 4 thermistors and combining them into 1 output whilst also displaying all 4 on an LCD bargraph). It's more or less finished but probably needs a few tweaks
And how are you deriving a voltage feed from the Arduino? If it's from a PWM pin and simple RC smoothing filter, then you need to take the source resistance of the RC filter into account. If you follow the RC filter with an op amp used as a unity-gain buffer, then its output resistance will be low enough to ignore.