Soil Moisture, DHT11 & DHT22 Sensors Behavior Observance and Calibration (SM2DSBOC)

Overview

The intention of this experiment is to see the behavior of different sensors in different mediums, different ADCs from various MCUs and one external ADC, and contrast results. It is crucial to verify that sensors data will demonstrate consistent outcome to rely on the sensors in future applications.

Although cheap and not certified sensors were used in the experiment, the intention is not to show the sensors' precision but rather that their modes/tendencies are similar.

Three different MCUs have been used: Whisper Node AVR based on ATmega328p, Arduino MKR1000 based on SAM D21, and ESP32 Hi-Grow design. The soil moisture sensors produce analog input, thus, different ADC modules were involved with different precisions. The following table shows the of used ADC modules

Node	ADC type
Whisper Node:	Internal ADC, 10 bits precision
Hi-Grow ESP32:	Internal ADC, 12 bits precision
Arduino MKR1000:	External ADC, TI ADS1115, 16 bits precision

In the next sections sensors' connections, experiment configuration, and data outcome and analysis are revealed.

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Experiment configuration

The experiment configuration was as exposed in the next scheme. The equipment was placed in the laboratory environment and later moved to the office TD1125.

        WiFi (UDP)   RX:16,TX:17                                  RX:D0,TX:D1
              ╤    ┌─────────────────────────────────────────────────────────────────┐       ┌───────┐
              └──┐ │  RX:27,TX:26    RX:13,TX:14   ┌──────────────────┐              │   ┌───┤ DHT22 │
                 │ │ ┌─────────────────────────┐   │     ┌───────┐┌───┴───┐          │   │   └───────┘
    ┌────┐ SPI ╔═┷═┷═┷═╗ ┌─────┐             ╔═┷═══┷═╗ ┌─┤ DHT22 ││ SHS85 │        ╔═┷═══┷═╗   ┌───────┐         
    │ SD ├─────╢ ESP32 ╟─┘ ┌───┴───┐         ║  MKR  ╟─┘ └───────┘└───┬───┘        ║  WIS  ╟───┤ SHS85 │         
    └────┘     ╚══┯═┯══╝   │ DHT11 │         ╚═══┯═══╝           ┌────┴────┐       ╚══┯─┯══╝   └───┬───┘        
                32│ │33    └───────┘             │ I2C           │ HIH8121 │        A1│ │A3   ┌────┴────┐         
                  │ └──────┐                 1 ┌─┴─┐ 0           └─────────┘          │ │     │ HIH8121 │         
                  └────┐   │   ┌───────────────┤ADC├────────────┐   ┌─────────────────┘ │     └─────────┘           
                       │   │   │               ┤   ├────────┐   │   │   ┌───────────────┘              
                  ____┍┷┑__│__┍┷┑_____       3 └───┘ 2 ____┍┷┑__│__┍┷┑__│______
                 ╱    │ │ ┍┷┑ │ │ ~  ╱│               ╱ ~  │ │ ┍┷┑ │ │ ┍┷┑  ~ ╱│
                ╱  ~  ╲.╱ │ │ ╲.╱   ╱ │              ╱     ╲.╱ │ │ ╲.╱ │ │   ╱ │
               ╱    ~     ╲.╱  ~   ╱  │             ╱ ~  ~     ╲.╱   ~ ╲.╱  ╱  │
              ╱___________________╱  ╱             ╱_______________________╱  ╱
              │                   │ ╱              │                       │ ╱
              │___________________│╱               │_______________________│╱

Sensors' Connections

SPI SD and ESP32 connection

       SPI SD       ESP32
        ~────┐     ╔═══~
          3V3├─────╢3V3
           CS├─────╢5
         MOSI├─────╢23
          CLK├─────╢18
         MISO├─────╢19
          GND├─────╢GND
        ~────┘     ╚═══~

DHT22 and MKR1000 connection

        DHT22       MKR1000
        ~────┐     ╔═══~
          VCC├─────╢5V
         DATA├─────╢A1
          GND├─────╢GND
        ~────┘     ╚═══~

DHT22 and Whisper Node connection

        DHT22       Whisper Node
        ~────┐     ╔═══~
          VCC├─────╢5V
         DATA├─────╢A0
          GND├─────╢GND
        ~────┘     ╚═══~

DHT11 is internally wired to the ESP32, though the configuration is as following

         DHT11       ESP32
         ~────┐     ╔═══~
           VCC├─────╢5V
          DATA├─────╢22
           GND├─────╢GND
         ~────┘     ╚═══

SHS85 and HIH8121 are connected to the Whisper Node through the I2C interface.

   SHS85 & HIH8121  Whisper Node
        ~────┐     ╔═══~
          VCC├─────╢5V
          SDA├─────╢D18
          SCL├─────╢D19
          GND├─────╢GND
        ~────┘     ╚═══~

SHS85 and HIH8121 are connected to the Whisper Node through the I2C interface.

   SHS85 & HIH8121  MKR1000
        ~────┐     ╔═══~
          VCC├─────╢5V
          SDA├─────╢11
          SCL├─────╢12
          GND├─────╢GND
        ~────┘     ╚═══~

Data Outcome

Artificial Substrate

The first part of the experiment consisted in using a special substrate inside the boxes which resembles the soil properties. On 29/01/2020 both boxes were filled with water. The substrate has been completely dry on 19/02/2020. During this period temperature, humidity and soil moisture data were recollected using different sensors. The data are visualized in the following sections.

Common graphics

Take heed that the samples mkr_0 and and mkr_2 are placed in the same box and mkr_1 is placed in different box.

Soil Moisture per Node

Temperature per Sensor

Humidity per Sensor

Real Soil

The second part of the experiment consisted in using the real soil recollected near the TI building. On 20/02/2020 both boxes were filled with water (around 200ml each). The sensors data are visualized in the following sections.