[NLRS] RF read water meters

[Doug Reed]

They replaced my meter last month in Maplewood. I haven't bothered to 
try and find what frequency it operates on. The meter they installed 
here works from scavenged power, most likely from the water flow winding 
a spring until it trips to drive a magnet and generate a voltage spike 
in a coil. At least that is the way I'd probably build it. I don't 
really like the spring option because it might break, but how many 
mechanical watches ever broke a main spring?.... Whatever it is has to 
be designed for more than 20(?) year MTBF or the water company isn't 
going to want it.

I'd tend to go for a simple burst transmission with an ID code and a 16 
or 24-bit pulse count for the water usage. The TX would be random based 
on water usage and if any packet was missed, the next would have the 
most current data.

ITI/GES used to build battery powered alarm sensors using AM pulse 
position burst transmissions at 320MHz, about 10-20mw RF output. The 
cheap receivers were designed to hear a minimum 2mw transmitter at 
500-600 feet LOS. The best receivers we sold would hear the TX at 
2100-2500 feet, or about 1/2 mile. This technology was 20 years old and 
would have been easy to integrate into a water meter. These days the new 
products are using ASIC chips with the RF and other electronics 
integrated on a single chip. Lower parts count should improve 
reliability.... I would choose to use 434MHz or another low-power band 
rather than 915MHz if I could help it.

I wouldn't expect the meter to have an active RX-TX system as I've heard 
suggested because that would require a more reliable power source that 
I've described. But if your water meter mounts outside, it might have 
solar cells. If it has an AC power connection indoors, then it might 
have a RX-TX polling or mesh system. On the other hand, maybe the water 
wheel generator has more power capability than I'd expect. It should 
certainly be capable of more "work." Of course this is all pure 
speculation on my part, although I was involved in a similar 
demonstration project 20 years ago....

73, Doug Reed, N0NAS.