Using the new method of measurement, described in this post, I could successfully collect some meaningful data. This time, the read values are the exact values of the final sensor without a different kind of oscillator.
I watered the plant at day zero with quite a great amount of water. From there you can see how the frequency slowly rises, while the soil in the flower pot starts to get dry. There is a small measurement error between day two and three. Here I had a short power loss and no data was recorded which resulted in some zero records.
The reason why the water seems to dry up much faster at the end has to do with the weather. It got cold and the air humidity went down, which dried up the soil much faster than in the previous period.
It is very nice to see how stable and predictable the measurements are over this long time period. There are some fluctuations, which may affect the behaviour. In the worst case you get the flash signal only for a short time on and off, until the soil is dry enough to permanently enable it. If I look at the data, this usually will happen over a transition period of two to four hours which seems acceptable.
I am still working to find the best way to seal the foot part of the sensor. Here I found an epoxy coating is the easiest thing to do and get the best results. Now I try different resins and hardener combinations to find the best one for my dipping process.
After this step, I will write the next part of my article series with all the details about this finalising work on the project. Another topic will be the manual for the sensor.
If you have questions, miss some information or just have any feedback, feel free to add a comment below.