I have recently been pretty bad at keeping my house plants alive. I need to add reminders to take care of my plants, and I usually end up ignoring them as "I'll do it when I get home", and then I almost never do. Wouldn't it be nice if the plant could tell you that it needs attention?
Plants don't have faces to express themselves, so what if the micro:bit could work for that purpose?
Excluding cacti, the one thing that plants usually need the most is ground moisture. How is moisture measured? The internet says that conductivity is a pretty good indicator.
So with a simple Ohmmeter we could measure the increase/decrease in resistance and by setting a few reasonable thresholds we can tell what the resistance corresponds to in terms of moisture levels.
The nails were used as ground probes, one connected to power and one connected to
pin0. The resistor was used as the "known" resistor for the ohmmeter. To replicate this you could use any resistor/ground probes/cabling. Just make sure the code is adapted for the resistor and that the probes are resistant to corrosion.
Also it goes without saying that you should keep the micro:bit at a safe distance from water and dirt ;)
In terms of programming, I set the micro:bit to display a happy, ok or sad face depending on the value of the resistor. Finding the correct thresholds was tricky as they can vary depending on the soil, distance between the probes etc. (code)
So, without further ado here's a watering demo of one of my plants (which I kept without water for a few days for that purpose as you can see from its horrible condition!):
As you can see with a bit of watering the plant becomes "OK" and with a bit more it becomes "Happy" ;)
A few potential extensions to this project (probably more important for outdoor plants...):