An Orbit 52212 has a Holtek HT67F30 MCU that reads a Magnetic Reed Switch.
I removed the electronics and replaced the reed switch with an Allegro A1190LUBTN Hall sensor which has two states, one where it is a 4.5mA current source and another where it is a 14mA current source. It is used to control the current in a CAT5 pair. The pair terminates on a 100 Ohm resistor. At 4.5mA the voltage on the 100 Ohm resistor is not able to bias an NPN transistor that pulls down the ICP1 pin of an ATmega328p, but when it switches to 14mA the NPN is biased and pulls down the ICP1 pin. So I can use the capture times to accurately measure flow rate and count the pulses from the flow meter.
Such a setup can allow the hall sensor to be placed very far away from the AVR.
More notes at: https://github.com/epccs/Document/tree/master/FlowMeter