I've been thinking about building up a DIY flow meter for my return pump, to see what it's actually putting out, and be able to tune my system a little better. However, I don't have an Apex, and I'm not about to plunk down the $$$ on one, plus the extra for the new flow meter kit they have. What I'm looking for is a relatively inexpensive DIY solution.
I'm figuring it will be based on an Arduino (or similar SBC), but my question is really more based on the sensor itself. Amazon is flush with hall effect sensors, most appear to be fairly inexpensive (less than $20), but how accurate are they really? Does anyone have a favorite brand/supplier of the sensors that I could put inline with my return?