Soil & liquid
Soil moisture, water chemistry, liquid level and flow are four different measurements. Decide which one you need before comparing probes.
Capacitive soil probes, pH/EC/TDS chemistry kits, RS485 water-quality sensors, contact and non-contact level sensors, and turbine flow meters — about 80 listings for anything involving soil or liquid sensing.
- Resistive prongs like the Adafruit Simple Soil Moisture Sensor corrode in soil over time; DFRobot's Gravity Analog Capacitive Corrosion Resistant Soil Moisture Sensor has no exposed electrodes and suits long-running irrigation builds.
- Water chemistry is its own branch: Gravity Lab Grade pH and EC kits (K=1 and K=10 cells), analog ORP and turbidity meters and Grove pH/TDS kits all need probe calibration and a signal-conditioning board. RS485 Modbus probes now expand this considerably — dissolved oxygen, chlorophyll, ammonia nitrogen, residual chlorine, turbidity and multi-parameter soil sensors (NPK, EC, pH, moisture) communicate over a transceiver rather than a direct ADC pin.
- Level sensing splits into contact (Grove Water Level 10cm, the float-and-reed Water Level Switch) and non-contact (Gravity capacitive through-wall sensors, the Optomax optical sensor, and an 80GHz mmWave UART sensor rated to 40m).
- Flow is pulse counting: the YF-B3 and Gravity G1/2–G3/4 turbine sensors output a pulse train you count on an interrupt pin.
