If this is the original flow meter proposal then surely you can get the tach signal out of the meter without a PIC. If it's the dP method, then feeding it back via the tach signal seems a bit round the houses. Surely better to get a A/D via sireal, usb (or even SMBus
). There's a lot more monitoring you can do once you have a multichannel A/D, such as pump power consumption (with a transducer), temp and whatnot.