For the first semester of the fourth year of our engineering school, we choose to work on a agriculture monitoring system. It has to measure some relevant value for the plant growth. The device must be autonomous in energy and use a LPWAN protocol.

Step 1: Step 1 : the Components of AGRI-2-EYE

Microcontroler :

STM32L432KC

Sensor :

Outside Humidity : DHT22
Outside Temperature : SMT172
Ground Humidity : SKU SEN0 193 https://wiki.dfrobot.com/Capacitive_Soil_Moisture...
Ground Temperature : Grove 1019919
RGB : Grove TCS34725 http://wiki.seeedstudio.com/Grove-I2C_Color_Sensor/
Light intensity : Grove 101020076 http://wiki.seeedstudio.com/Grove-Luminance_Sensor...

LPWAN Communication :

Wisol SFM10R1

Alimentation :

Solar Panel 6V - 2W

Screen display :

ARCELI SSD1306

Step 2: Step 2 : Agri-2-EYE Prototype

Step 3: Step 3 : Project Schematics

For the project we need 3 PCB :

a power supplier PCB
an interfacing PCB
an outside sensor PCB

Step 4: Step 4 : Mbed Development

The Arm Mbed IoT Device Platform provides for users an online platform easy to use for Mbed compatible hardware. It allow access of huge amount of library. The Mbed community develops library, gives access to exemple software for compatible device and helps users for their issues.

How does Mbed Platform work?

The first step is to go to the Mbed website : https://www.mbed.com/en/
Create an account
Go to compiler menu and chose your device : STM32L432KC (our microcontroler)
Create a project
Import useful library ex : DHT library
Start the program
Compile the code
Export to the device with the micro-usb port connect between the PC and the STM32L432KC

Pay attention to the pin map to correspond with the schematics.

Step 5: Step 5 : Sigfox Configurations

For the LPWAN Protocol we choose a Sigfox Module. Sigfox protocol is really useful for IoT application because is communication not consume a lot of energy, and it also can send data in long range of distance. It communicates with the backend of Sigfox. In this project the module help to transmit data to the IoT platform.

You need to connect the module with the CPU (Like in the picture 2).

To send data you have to use AT command format. For exemple :

AT send OK,

AT$T? return the temperature value.

We use this format to send each sensor values.

Step 6: Step 6 : Agri-2-EYE Codes

We develop an cpp code based a sensor library. In the main you can find all code you need to understand how we configure the screen display, the transmission...

In the picture you can see how we send the sensor value.