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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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 ____┍┷┑__│__┍┷┑__│______
╱ │ │ ┍┷┑ │ │ ~ ╱│ ╱ ~ │ │ ┍┷┑ │ │ ┍┷┑ ~ ╱│
╱ ~ ╲.╱ │ │ ╲.╱ ╱ │ ╱ ╲.╱ │ │ ╲.╱ │ │ ╱ │
╱ ~ ╲.╱ ~ ╱ │ ╱ ~ ~ ╲.╱ ~ ╲.╱ ╱ │
╱___________________╱ ╱ ╱_______________________╱ ╱
│ │ ╱ │ │ ╱
│___________________│╱ │_______________________│╱
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
~────┘ ╚═══~
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.
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.
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.
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.
This section can be dedicated to further analysis as RMSE, norm, etc.