Just received Flow.com’s low cost (plastic) water meter with dry-contact reed switch (2-wire) pulse output made by Assured Automation. Tested unit with pulse counter to confirm that 1 pulse = 1 gallon. Very good product. This ought to be a perfect match for opensprinkler flow sensor connectors. Because there were some fractional scaling issues when calibrating pulses to GPM with the Hall-effect sensors in opensprinkler’s software settings. That should be no longer an issue with this particular meter (WM-PC series)
IMHO trying to monitor fractions of gallons of water flow is overkill for an irrigation system, even if you’re using just microsprays and small misters. Typically the 3-wire Hall-effect flow sensors are going to do that because they’re not designed for large flows as you typically have in irrigation. They’re better at metering precision with smaller flow. Plus if you’re using batteries to get signal, it’s a non-stop chore to keep swapping out batteries when you lose pulse output. Reed switches don’t need to be powered to produced pulses.