STEMMA capacitive soil moisture sensor improves on resistive style for around $7.50
Most low cost soil sensors are resistive style, where there’s two prongs and the sensor measures the conductivity between the two. These work OK at first, but eventually start to oxidize because of the exposed metal. Even if they’re gold plated! The resistivity measurement goes up and up, so you constantly have to re-calibrate your code. Also, resistive measurements don’t always work in loose soil.
This design is superior with a capacitive measurement. Capacitive measurements use only one probe, don’t have any exposed metal, and don’t introduce any DC currents into your plants. They use the built in capacitive touch measurement system built into the ATSAMD10 chip, which will give you a reading ranging from about 200 (very dry) to 2000 (very wet). As a bonus, it will also give you the ambient temperature from the internal temperature sensor on the microcontroller, it’s not high precision, maybe good to + or – 2 degrees Celsius.
|STEMMA capacitive soil moisture sensor improves on resistive style - Geeky Gadgets