I plan to make around 20 more of these sensors, so I am still in the process of optimizing the circuitry, but so far this is what I've done for my prototype node:
Regarding Solar powered:
I used a solar charger module from Seeed Studio (Li-Po rider); its pretty neat, in that it switches power from solar to battery only when needed. Moreover, v1.2 supplies up-to 350mA. I connected a 3.7V 2000mA Li-Polymer rechargeable battery and a 5V 100mA solar panel to this Li-Po rider which sources my Atmega328. The battery continues to charge while the sensor node is sleeping. I logged the sensor data in the ATmega EEPROM every hour. (As it’s not wireless yet! - that's what brought me to 'MySensors')
After researching about the different options available, I bought a few different ones including a Watermark 200SS and Delmhorst GB-1. They are all based on the same principle – change in soil water tension – affecting resistance value. Watermark claims that their sensors do not dissolve. Their stainless steel jacket seems to gives it an increased life. I also created my own sensors, based on some information found on Van der Lee Vineyard blogsite. A simple series of resistance measurements from completely wet to completely dry for these sensors – home made as well as the ones I bought, helped me calibrate my home made sensors. I now feel comfortable using my own sensors and have acquired a reliable degree of accuracy and precision on my little tensiometer. Which is why I am ready to expand them into a network.
- I'm looking for different ways to log this data and have it available on simple graphs. (Currently, studying various controllers mentioned here. Btw, it is possible at all to use EasyIoT directly on a PC instead of on a Raspberry Pi?)
- I've bought some nRF24L01 modules with PA and SMA antenna and will perhaps have to design a simple 3.3V regulator to source it directly from the the Lipo Rider board (since the pro mini wont be able to meet my current requirements(?) for a longer range - I want to be able use them on maximum power for long range.)
I will try to keep posting more updates as I have them.
Meanwhile, any help/ideas are appreciated.