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RAK12035 WisBlock Soil Moisture Sensor Module Datasheet

Overview​

Figure 2798: RAK12035 WisBlock Soil Moisture Sensor Probe

Description​

RAK12035 is a soil sensor probe module based on the ATTINY441-SSU microcontroller from Atmel. It uses capacitive sensing to measure moisture. A 1 MHz square wave is the output from the chip through a resistor into a big pad, and the surrounding ground plane acts as a parasitic capacitor. Both the resistor and the capacitor form a low-pass filter whose cutoff frequency changes when there is a change in capacitance.

The soil around the sensor acts as an electrolyte whose dielectric constant changes depending on the amount of moisture in it, resulting in changing the capacitance of our makeshift capacitor too. The filtered square wave is fed into a peak detector, formed by a diode and capacitor. The diode allows the positive peaks to go through, while the capacitor stores the maximum voltage of those peaks. The voltage is measured by an ADC in the MCU. An NTC element is used to measure the temperature of the soil.

RAK12035 is a separate soil moisture sensor probe that can be connected to the RAK12023 module.

Because you need to bury the RAK12035 sensor probe into the soil, the electronics on the PCB of the soil sensor, together with the cable, are covered by a shrinkable tube for additional protection from getting wet.

Features​

  • Separate connector PCB RAK12023 is required.
  • Measures soil moisture
  • I2C address is programmable
  • Calibration via software
  • Chipset: Atmel ATTINY441-SSU
  • Module size: 18.1 x 149 mm

Specifications​

Hardware​

The hardware specification is categorized into four (4) parts. It shows the chipset of the module and discusses the pinouts and their corresponding functions and diagrams. It also covers the mechanical characteristics that include the tabular data of the functionalities and standard values of the RAK12035 WisBlock Soil Moisture Sensor Module.

Chipset​

VendorPart number
AtmelATTINY441-SSU

Pin Definition​

The pin order of the connector and the pinout definition of the RAK12035 is shown in Figure 2.

Figure 2799: RAK12035 Pinout Schematic
NOTE
  • Only I2C related pin, SENSE_HIGH, 3V3, and RESET are connected to the module.

Mechanical Characteristics​

Board Dimensions​

Figure 3 shows the board dimensions of the RAK12035 Module.

Figure 2800: RAK12035 Board Dimensions

Schematic Diagram​

Figure 4 shows the schematic of the RAK12035 module.

Figure 2801: RAK12035 WisBlock Module Schematics
MCU Configuration Circuit​
Figure 2802: MCU Configuration Circuit
Sensor Circuit​
Figure 2803: Sensor Circuit
Thermistor​
Figure 2804: Thermistor