I think I am largely MCU agnostic, although preferably something where I can use Arduino since I am familiar with that. Good to know that ESP8266 is more energy efficient. I have seen this video which demonstrates that the ESP8266 can run off 2 AA batteries for 425 days [1].
Another thought I was having was to write a mobile app that as volunteers walk by the sensor would send data to their phone, which would then forward it to my backend. I suppose this is a mesh network of sorts? Not sure if this is feasible or a good idea though :/
Another option would be LoRa - it’s pretty long range. The problem would be that could add a lot to power usage. Though 6h should be plenty of time - wake up, send a small packet, sleep for 6 hours.
You would have a central LoRa receiver in a place that can reach all of the sensors. How far apart are the trees?
Other than that, I would suggest testing out lots of different hardware. I bought several different boards before any decisions were made, and I’m glad I didn’t stick to just one. Costed me maybe $30 to buy a gamut of devices and now I’ve settled on a single one that does what I need.
Also, make sure you’re flashing with the largest image size you can, if your code becomes too large. For me I had to enable an option in the board settings to use the full memory space.
Lastly, one thing you should do is the low power option. See which board supports it the best. Then, what I would do at startup is turn on all the sensors, collect and send data right away, then turn all your sensors off. Do ultra deep sleep for 6 hours. then when it wakes up, don’t bother doing any kind of loop to the beginning - hard reboot. That avoids any problems with memory allocation becoming too large somehow over the course of the program, since it always starts fresh (which is all you need!). I’m not sure the trade off here but for me, I reboot every 12 hours and it works great. (I would do it after every scan but I don’t delay between scans for more constant data, so it would be a lot of set up every single minute).
The trees are all pretty close to each other, about 3-4 city block radius (map of trees [1]). The issue is that as far as I can tell there is no existing LoraWAN gateway on The Things Network I can tap into [2], which means I will have to setup my own gateway. Which is fine, but it may prove to be difficult to get this onto a tall building since I am just an apartment dweller. At the very least I can put the gateway in my apartment window.
Another thought I was having was to write a mobile app that as volunteers walk by the sensor would send data to their phone, which would then forward it to my backend. I suppose this is a mesh network of sorts? Not sure if this is feasible or a good idea though :/
[1] - https://youtu.be/IYuYTfO6iOs?si=oLuJiGxdQ8VHyu29&t=837