I have a simple pump based residential sprinkler system. I am looking at purchasing a smart controller, and the Rachio Gen2 is on my short list. But, I would like an affordable flow meter to use for a few purposes (listed in order of priority).
1) Protect my pump and solenoids from overheating when there is no flow (shut off if the flow is too low). Solenoids go bad, and when there is no flow, it can damage the pump due to overheating because water flow keeps the pump cool. If the pump goes bad, I don't want the solenoids to be damaged due to overheating with no water to help keep them cool.
2) Help in recognizing broken pipes and sprinkler heads, and shutoff if the flow is too high.
In both cases, I would like some sort of obvious error indication on the panel and possibly an error email.
On the subject of affordability, all the sensors on the list so far are expensive (>$200 with the sensor T included). Why not also support inexpensive (<$30) 3 wire flow sensors, such as the ones sold by TmallTech on Amazon? (Search on Amazon for TmallTech flow. One size is shown at the link below.)
It is a pulsed output, but requires power. Even if an external DC power supply is needed (not supplied by the controller), and even if an external electronic switch is needed to mimic breaking a contact to simulate a 2 wire sensor (not sure if that is necessary - depends on the controller interface), that is still MUCH cheaper than the expensive flow sensors.
I have also considered to adapt in (via a T) an inexpensive paddle-type flow switch to protect in the no-flow situation, such as this one at Amazon:
I could connect it into the second rain sensor input, or in series with a rain sensor if I use two rain sensors.
In both the flow sensor and flow switch cases, the controller would need to wait 15 to 60 seconds after the pump turns on before deciding if the flow is correct.
I have only found one residential controller that does the above, but you have to spend yet more money on another interface module to read the flow sensor (which makes the total cost more than the Rachio Gen2), and it says it only supports 2 wire sensors. I could make the simple circuit to convert 3 wire to 2 wire, but I would prefer not to have to do it myself.
On a related item (pump protection), I would also like to attach an inexpensive temperature switch to my pump and/or motor housing, and have that signal go to the controller so it can read that there is an error and turn off the system. A simple bimetal temperature control switch is cheap, and can be bought at varying temperatures from Amazon (for about $9 for 10 switches).
Again, I could put it inline with the rain sensor or a flow sensor to cause the system to be shutoff, but it would be nice if there were a separate input so the error source could be identified. (I could build an error status indicator circuit for this, but I prefer the controller to do it.)