I love to have a lot of plans in my room, unfortunately I always forgot to water them and the result is that all of more demanding plans are dead in no time. It seems that only ferns and cactuses can survive with me! That's why I decided to make and device that could measure humidity of soil and warn me if it's too low.
In this post I will present a prototype that I made, it was created to check if this way would be enough or if I should use other methods (presented later in the post). The idea is to measure resistance of the soil - when it's dried, then of course there's not a lot of water in it, so it can't conduct electricity very well. As a control unit I hoped to use an old Arduino that I bought a couple of years ago. The device would be plugged to analog inputs, results would be stored in EPROM memory to protect them against power loss (additional piezo with built-in generator).
The device contains two electrodes plugged to the soil and a small capacitor plugged in parallel to filter noises. There's also a fotoresistor (and a capacitor plugged in the same way) to measure light intensity, that's because I wouldn't like to be waked up in the middle of the night to water the plants. The device would use two digital inputs of the Arduino.
Below you can see the device.
It works, but the results are unpractical:
- different soil conduct different amount of electricity, so the device should be tweaked to each plant separately,
- the capacitor plugged in parallel with electrodes can't discharge, probably I should also add a resistor in parallel to him
- electrodes should be protected against moving or connecting in the ground.
I decided to leave this approach and make another check in the future:
- I will place in a pot a small, hermetic container, it will be dug into the ground,
- in this container I will place humidity sensor (a popular and inexpensive one that can be purchased online).
The humidity in the container will reflect directly humidity of the soil because it will be isolated from external environment.
That's what I will do, I didn't buy the sensors, so it's still waiting.