Newbie designing a remote sensing network
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I have two detached structures about a half mile from each other and about the same distance from my house. I want to monitor several things at both structures: electric power off or on; pulse count on a 2 inch water meter; valve open (simple pressure switch); and solenoid contacts open/closed. These sensors are already installed at both locations.
I want to replace the commercial alarm company equipment and their two cell phones, with an arduino type controller, and send data via wifi to my home location. I think this is doable with the right wifi antennas aimed at hotspot at my home. But I need some guidance/help in figuring out how to put it all together.
Is this doable? I'm beginning the design stage and want to cost it out.
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Wifi should be possible. To get "full" signal strength, the antenna needs to be at a height of at least 5m/16ft. See https://www.everythingrf.com/rf-calculators/fresnel-zone-calculator
However, you might not need full signal strength so you can probably use a lower height. Place the antenna as high as possible though.
Depending on where in the world you are, you might be able to use directional antennas like https://www.ebay.com/itm/REMO-BAS-2301WiFi-Outdoor-2-4GHz-Wireless-High-Gain-WiFi-Antenna-With-RP-SMA/352704967539?hash=item521edab373:g:R70AAOSwEo1dGBqa
An alternative to using wifi is to use MySensors with a long-range radio like rfm69 or rfm95/98. See https://www.mysensors.org/build/connect_radio#rfm6995-&-arduino for connection instructions and https://www.mysensors.org/about for what the MySensors library can do for you.
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@mfalkvidd Thanks for the quick reply. Problem I have is that all three locations are in dense forest, so LOS is a problem. Would rf have the range to reach the three locations?? I've got a lot of learning to do.
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@giacobea hard to tell without doing field tests, but getting working wifi will probably be hard
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@giacobea Dense forest also suggests heavy rain which could also cause problems depending on the radio you use.
Lower frequencies will better penetrate, but directional antennas to give you power gain will also be considerably larger.
A chain of repeater modules with solar or wind power might be a solution, depending on how often the signals need to be sent and how much sun/wind you get.
There is also the option to 'bounce' the signals off of high buildings or mountains, but that's an area I can understand if you don't want to get into that sort of thing.
Maybe you can fit a repeater to a high tree/tower/etc?
As @mfalkvidd said though, field tests are the way to go and modules are not too expensive (and can be re-used in other projects if not suitable).
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Wifi?
Wouldn't it make more sense to use MySensors with RFM69 433Mhz? Or even Lora radio modules? Those are designed for long range.
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Thanks for the replies so far, let me clarify. Ultimately I want to end up with a system that: sends an email to an end user when a sensored event occurs at either remote location, without human intervention. Example: electric Power off or on; low water pressure in a pipe on or off; low water level in a tank ; and a daily pulse count being read at the 2inch water main meter.
My constraints: There is no direct line of sight between the three loctions, which are roughly aligned on a single axis: home, loc1, loc2. All locations are surrounded by 50' trees. Loc1, in the middle, is at the highest point.
All locations have commercial ac power, but would need to have a battery backup. Am assuming a gateway at loc1 and loc2 with sensors hardwired to each gateway. So the problem I'm attempting to solve is the comm link from each loc to my house where I can get the data onto the web unless it is already in the right format (email). There's no actuators involved.
Thanks @skywatch and @alowhum for your suggestions, getting me thinking rf is the way to go. Looks like the Lora may have the range I need: 2500' and 3000' between the locations. And like @mfalkvidd y'all are right, field testing is going to be required. I just need to figure out how the comm needs to work.
Would rf, from say an rfm6995 or LoRa, be strong enough to reach through the undergrowth, or does it need an antenna above the trees?
Thanks to all for your help.
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@giacobea my tests with rfm95 (in LoRa mode, 433MHz) showed an rssi of -101 to -112 at a distance of 1.5km (almost a mile). That was line of sight, so expect worse in your situation. rfm95 can receive down to -148 so there is some margin though, and your distance is shorter.
If the lower frequencies are legal in your area, choose the 433 or 169MHz versions (called rfm98).
You can probably reuse my code
https://github.com/mfalkvidd/FatLinkGateway
https://github.com/mfalkvidd/FatLinkMobileNode
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Perhaps a bit off the wall, but if the objective is an email out, are GSM signals strong enough even at another high point which does afford radio line of sight to the objectives?
Used this many years ago for remote monitoring, in one case the GSM atop a 5m pole with a wind generator attached topping up a pair of batteries, so completely self sufficient. Links to the metering points were low power RF, the landowner had no objections.
Only problems encountered were vandals climbing the pole, solved by a good coat of Copaslip
, and a Stag which regularly danced on a GRP cover to a flow meter chamber, to the great amusement of the gamekeeper 
