| I am so excited to see this! I've been working on a very similar project to monitor my outdoor vegetable garden using a raspberry pi and some ESP8266's. Like you, I'm using this as a project to better learn javascript, angular and django. It's in the very early stages, but I'm really loving the experience so far. Here's a picture of my setup.
http://imgur.com/a/BV188 I have a enclosure (that I recently made waterproof) that sits out in my garden that has the ESP8266 wireless chip in there, which works very similar to an Arduino with built in WiFi. I have it reading data in from a soil humidity / temp sensor, an air humidity sensor, a light sensor, and a air temperature sensor. That data gets sent back to a simple django webserver that I have running (indoors) off of a raspberry pi. It records all the sensor readings every 10 minutes and registers them to various plots in my garden. And then, if there are any big issues (no light for 2 days, lower than average soil humidity or soil temperature, etc), it texts me. Eventually I'll connect it to my irrigation system, but I don't trust it enough yet! I have the exact same problem with soil humidity sensors that you mentioned. I even sprung for some fancy ones (http://bit.ly/2sMNRnD) that claim to be waterproof. I cannot make them read useful information and, once it rains or I water outdoors, the sensors read 99% for the next few days. It's very frustrating and the missing piece to make all of this work. Like you, this started as a quick, month-long project and now it's become something a lot bigger :) I think eventually I'd like to build this out to be a vegetable garden planner, so I can plan my vegetable garden at the start of the season, monitor what's happening with them, and automatically trigger my irrigation system if needed. Anyway - it was great to read this! I'd love to hear how this project evolves and would be happy to share any of my experiences as I've put this together. P.S. And, it's a long shot, but if you (or anyone is reading this) figures how to accurately measure soil humidity temperature in a waterproof environment, I would be forever grateful! |
I don't understand TDR well enough to explain it, so I will let you search for your own info. The cheapest usable TDR sensor is about $350.
Tension has a simple analogy; a Slurpee (is that trademarked?) is easy to drink through a straw in the beginning, but it gets harder to pull the liquid up the straw as you drink more of it. That's tension and plants also struggle to pull the water from the soil depending on lots of factors including the composition of the soil, the amount of water present, drainage, etc.
There are several sensors that can be used to measure tension but none are accurate in all conditions, so people who want to measure tension tend to use multiple sensors of different types and triangulate on a useful number.
Large scale farming (in dirt across thousands of acres) is where the complex sensors are needed because the soil attributes are not uniform.
When you're gardening in a pot indoors or in a greenhouse with the same soil everywhere (because you bought bags of it), you can use those $0.43 resistance probes and just calibrate your watering amounts and intervals over time. Pump on for X units of time, ignore for Y units to let the water move through the soil, then sample every Z units until it needs more.