Thanks, I need some time to test the code snippets gratefully offered to help me use an Arduino and I will follow those up soon.
In the meantime, an interface between the flow sensor and sensing head unit using CMOS binary rate multipliers can work with 3 chips dropping pulses, for a flow meter which uses pulse counting. It consumes < 1mA standby battery power, 5-12V supply and doesn't need an active clock to function or any I/O voltage conditioning