The first long term measurement I made, to test the behaviour of the sensor over a longer time range was a failure. After the five days with the device introduced in this post, the readings made absolute no sense.
The sensor was not moved in the flower pot and the plant was once watered at the begin of the measurement. While it looked promising at the begin, the frequency suddenly went down again, which was very irritating. I am still investigating how this could happen.
To get closer to the real measurement of the final plant watering sensor, I started a new approach.
I soldered a header to one of the LED pads on a fully assembled plant sensor. Next I changed the device for the measurements.
Recently I had the problem some expensive components did overheat in my server rack. The ventilation was not optimal and I had to install additional fans. Because this rack is in my office and I like a quiet working place, the ventilation had to be as quiet as possible.
First I thought about buying a off-the-shelf product, but then I realised: If this controller does not work as I expect and the fans will spin too fast/loud, this will drive me crazy over time. So I decided to build a own fan controller. A very simple one, where I can write own code and tweak it until it runs as I like.
On the project page I describe how to build this particular controller. It is not meant you really reproduce this same controller exactly as shown, but maybe understand some basic principles to build your own controller.