Really glad to see that you got a flow sensor to work with OS, and thanks for sharing the code. I’ve done a bit of research myself a while back, and the flow sensor I tried (it’s a very cheap one like this: http://www.amazon.com/1-60L-Effect-Sensor-Counter-FS300A/dp/B00HR6BTYQ) sends out pulses very quickly and I didn’t think it was feasible for an interrupt pin (i.e. may be losing a lot of pulses). The one you used seems to pulse at a much slower rate and it’s perfect for an interrupt pin. Now that the signal can be read reliably to OS, the rest (display, logging etc) is just a matter of software changes. So I think this is a big step towards having flow sensor officially supported by OS firmware.
One quick question: where did you buy the NETAFIM meter? I would like to get one to test as soon as possible.
In terms of the hardware, my plan is to remove the power switch currently on OS and use that opening to fit a small connector wired to the flow meter. In the new batch of OS enclosures, the silkscreen above the power switch opening has been removed, particularly for this purpose 🙂