I have a medium sized Pear orchard and have a Hunter ACC 24 valve irrigation controller running the water system. Occasionally, the pump water from the irrigation district will shut off and the system shuts down the pump. It has a pressure sensor on the pump and a in-line flow meter that also will shut down for over flow or under flow. If the pump shuts down, the controller will sense low flow and start shifting to the next station, thinking theres a leak in the line on the station with low flow. Also, if the screen on the water box supplying the pump gets clogged, the pump will start cavitating and the flow will also go low, but not enough to shut off the pump. Both things I'd like to know about.
My problem is this system has no phone or internet access, and I'd like to be alerted whenever anything changes. I'd also like a temperature monitor to alert me of low temps. I have a GSM shield on a Uno (also have a Mega if need be) and have a simple SMS text message alert running that will send me texts when the pump shuts off, a low flow exists, or temp drops below a certain value. So far the software side works ok. I'm simulating the inputs for now. The hardware side is where I need help, please.
My two main questions: When the pressure switch on the 240v 10 hp pump output senses low, it trips a relay in the main breaker box that shuts the power off (the Hunter controller doesn't do this). I was thinking I'd intercept the relay output going low as a signal to the arduino? It's a 120v ac signal I think,, so I assume I could have it power another relay that switches a 5v signal to one of the digital input pins? Any idea on the best way to do this?
Second problem is monitoring the 2" flow meter. According to the manual that came with the sensor, it's a 2 wire 20 vdc signal that switches on / off or "clicks" as the water flows passed it. I think it is a paddle wheel type but haven't looked at it closely yet. I need to figure out a way to intercept the on/off pulses and convert it into a signal I can use to determine a low flow rate. It's wired to the ACC Controller through a sensor terminal and common terminal. Any ideas on my best options? Do I want to read across these two terminals (parallel) or in series? If it's a 20v dc signal I need to drop it to 5v, so would a simple voltage divider be enough?
Any help you could give me would be appreciated. There isn't any water at the pump at the moment so I can't run the system yet and determine what the actual output of the flow valve looks like, and I don't trust my electrical skills enough to experiment without blowing up my arduino finding the wrong solution first...