The Soil Moisture Sensor is a modern, completely sealed capacitive moisture sensor with temperature sensor and calibration saved in its internal EEPROM. It is using 1-Wire communication protocol and has 3 wire cable that is 2 meters long. Many sensors can be connected to a single 1-Wire Master. The temperature sensor is located in the top part above the soil. The electronics is completely potted in a sealing compound to withstand all kind of weather.
The sensor returns soil moisture humidity values from 0 to 100%. Measuring is done by two copper strips inside the inner layers of the 4 layer PCB. This way the contacts are not exposed to direct humidity and do not oxidize.
The sensor comes already calibrated. Calibration is done in the water. It is also possible to use sensor to measure water level.
Sensor is already supported in BigClown SDK with examples and projects. Arduino Library is also available.
Soil moisture sensor 0-100%
Fully digital design
1-Wire bus communication
Possibility to connect multiple sensors in parallel
Capacitance-to-digital converter ZSSC3123
Digital temperature sensor TMP112
Operating voltage range: 2.8 V to 5.5 V
Operating temperature range: -40 to +85 °C
Protection marking IP 68
We calibrate each sensor. The calibration saves data to to internal Soil Sensor EEPROM and ensured that every sensor returns the same value when its dry (0%) and submerged to the water (100%).
The calibration values are used when the raw values has to be converter to 0% - 100% range. If you use raw data from capacitance sensor only (or you use your own hardware/firmware reading the data) you can ignore the EEPROM data.
User can recalibrate its sensor by using the same calibration firmware we use.
Calibration has 11 points (0, 10, 20, 30, 50, 60, 70, 80, 90, 100%) and it is saved in the sensors' internal EEPROM. The structure is explained below and it is saved in three locations (banks) for redundancy.
In the Soil Moisture Sensor SDK there are functions to store the calibration points. You can also set text label to each sensor to name the sensor or the plant it is located.
Length = 8 B
Calibration Point 0%
Calibration Point 10%
Calibration Point 20%
Calibration Point 30%
Calibration Point 40%
Calibration Point 50%
Calibration Point 60%
Calibration Point 70%
Calibration Point 80%
Calibration Point 90%
Calibration Point 100%
Length = 64 B
The capacitance chip inside Soil Sensor in configured during manufacturing to the capacitance ranges that are the most sensitive according to the conformal coating thickness.
User do not have to do the calibration. The capacitance chip can be configured over I2C during the first 50 ms after power-up. Because the Soil Sensor is using 1-Wire to I2C converter that has quite long start-up time, it is not possible to configure the chip over 1-Wire. It is only possible over I2C just before the sensor is coated.