Most low-cost soil sensors are resistive style, where there’s two prongs and the sensor measures the conductivity between the two. These work okay for the price, but eventually start to oxidize because of the exposed metal, which increases the sensors’ resistivity so re-calibration is necessary because the analog output voltage changes for similar soil moisture conditions.
To get around the issue mentioned above, this design uses a capacitive measurement. This allows the sensor to use only one probe, to not have any exposed metal (preventing resistivity changes), and to avoid introducing any DC currents into the soil/plants where the measurements are taking place. These sensors use coplanar traces to create a high frequency output from the onboard 555 oscillator. Depending on the moisture levels of the soil where the sensor is inserted, we get a change between 400~1024 raw counts by reading the filtered output using a 10-bit Analog to Digital Converter (ADC) like on an Arduino Uno development board.
This Soil Moisture sensor uses a 3-pin JST connector that connects to a 3-pin female header (socket) connector. This makes it easy to work with and connect to a microcontroller, single-board computer, or solderless breadboard using Dupont-style jumper wires (e.g, Arduino, Raspberry Pi)
- Operating voltage: 4.5~5.5VDC
- Output Voltage: 0~3.0VDC
- Operating Current: 5mA
- Output type: analog voltage
- Interface: PH2.0-3P
- Dimensions: 3.86 x 0.905 inches (L x W)