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Description

Imported from GitHub: manupawickramasinghe/stm32-solar-gsm-sensor · commit 09f225f · license MIT

Description

Firmware and Hardware for Open-Source GSM Baased STM32 AgriSensor

README

stm32-solar-gsm-sensor

Firmware and hardware guide for an open-source, solar-powered agricultural sensor system based on the STM32 "Blue Pill" and a SIM800L GSM module.

This project is designed for remote environmental monitoring. It periodically reads data from multiple sensors based on DIP switch configuration, aggregates the data, and sends a summary report via SMS to a predefined list of phone numbers. It is optimized for low-power operation, making it suitable for solar or battery-powered deployments.

Features

  • Multi-Sensor Support with DIP Switch Selection:

    • DHT11 temperature and humidity sensor
    • DS18B20 waterproof temperature sensor
    • FC-28 soil moisture sensor
    • MQ2 gas sensor
    • 4-position DIP switch for enabling/disabling individual sensors

  • GSM Connectivity: Uses a SIM800L module to connect to the cellular network for sending and receiving SMS messages.

  • Periodic Data Reporting: The device wakes up every 5 minutes to take sensor readings from enabled sensors only.

  • Dynamic SMS Content: SMS reports include only data from sensors that are enabled via DIP switches. If no sensors are enabled, only timestamp is sent.

  • Averaged Data SMS: After a set number of readings (e.g., 12 readings over 60 minutes), it calculates the average sensor values and sends a consolidated report via SMS.

  • Multi-Recipient SMS: Sends the report to a configurable list of multiple phone numbers.

  • Network Timestamp: Fetches the current date and time from the cellular network and includes it in every SMS report for accurate logging.

  • Persistent Counter: Uses Flash memory emulation (since the STM32F103C8T6 does not have built-in EEPROM) to save its reading counter, ensuring it can resume its cycle even after a power loss or reset.

  • Remote Control via SMS: Comprehensive SMS command system for remote configuration and monitoring.

Hardware Requirements

  • Microcontroller: STM32F103C8T6 "Blue Pill" board.

  • GSM Module: SIM800L module (ensure it comes with a spring antenna and a valid 2G SIM card).

  • DIP Switch: 4-position DIP switch for sensor selection.

  • Sensors:

    • DHT11 Temperature and Humidity Sensor (Pin: PB1)
    • DS18B20 Waterproof Temperature Sensor (Pin: PB0) with 4.7kΩ pull-up resistor
    • FC-28 Soil Moisture Sensor (Analog Pin: PA1)
    • MQ2 Gas Sensor (Analog Pin: PA4)

  • Pin Assignments for DIP Switches:

    • DIP Switch 1 (DHT11): PC13
    • DIP Switch 2 (DS18B20): PC14
    • DIP Switch 3 (Soil Moisture): PC15
    • DIP Switch 4 (MQ2 Gas): PB12

  • Programmer: FTDI FT232RL USB-to-Serial adapter for flashing the firmware.

  • Power Supply:

    • A stable power source for the SIM800L is critical. A 3.7V LiPo battery or a dedicated buck converter capable of supplying at least 2A peak current is highly recommended. Powering the SIM800L directly from the Blue Pill's 3.3V pin will cause instability.

Software & Setup (Arduino IDE)

This project is built using the Arduino IDE with the official STM32 core.

  1. Install Arduino IDE If you don't have it, download and install the latest version of the Arduino IDE.

  2. Install STM32 Board Support Open the Arduino IDE.

    Go to File > Preferences.

    In the "Additional boards manager URLs" field, paste the following URL:

    https://github.com/stm32duino/BoardManagerFiles/raw/main/package_stmicroelectronics_index.json

    Go to Tools > Board > Boards Manager....

    Search for "STM32 MCU based boards" and install the package by STMicroelectronics.

  3. Install Required Libraries You need to install three libraries for the sensors.

    Go to Tools > Manage Libraries....

    Search for and install each of the following libraries:

    • DHT sensor library by Adafruit

    • OneWire by Paul Stoffregen

    • DallasTemperature by Miles Burton

  4. Configure the Code Open the .ino sketch file in the Arduino IDE.

    Modify the phoneNumbers array to include the recipient phone numbers you want to send the SMS reports to. Make sure to use the international format (e.g., +94...).

    String phoneNumbers[] = {"+94719593248", "+94719751003"};

Flashing the Firmware (Manual Upload)

Since this project uses an FTDI adapter, you cannot use the standard "Upload" button in the Arduino IDE. You must compile the binary and flash it manually using a command-line tool.

Step 1: Compile and Export the Binary

In the Arduino IDE, select the correct board settings:

  • Tools > Board: "STM32 MCU based boards" > "Generic STM32F1 series"

  • Tools > Board part number: "Bluepill F103C8"

  • Tools > Upload method: "STM32CubeProgrammer (Serial)"

Go to Sketch > Export compiled Binary. This will compile your code and create a .hex and .bin file in the sketch folder.

Step 2: Install stm32flash

This is a lightweight, reliable tool for flashing STM32 devices via UART.

Open a terminal on your Linux machine and run:

sudo apt update
sudo apt install stm32flash

Step 3: Set Up Hardware for Flashing

This is the most critical part. You must put the STM32 into its hardware bootloader mode.

  • Set Jumpers:

    • Set the BOOT0 jumper to the '1' position (HIGH).

    • Set the BOOT1 jumper to the '0' position (LOW).

  • Wire the FTDI Adapter:

    • FTDI GND -> STM32 GND

    • FTDI TX -> STM32 PA10 (RX1)

    • FTDI RX -> STM32 PA9 (TX1)

  • Connect and Reset: Connect the FTDI adapter to your computer. Now, press the RESET button on the Blue Pill board. The board is now waiting for programming commands.

Step 4: Fix Serial Port Permissions (One-Time Setup)

On Linux, your user needs permission to access serial devices.

Add your user to the dialout group:

sudo usermod -a -G dialout $USER

IMPORTANT: For this change to take effect, you must log out and log back in or reboot your computer.

Step 5: Flash the Firmware

Open a terminal and navigate to your Arduino sketch directory where the .bin file was exported.

Run the stm32flash command:

stm32flash -b 115200 -w YourSketchName.ino.bin -v -g 0x0 /dev/ttyUSB0

  • -b 115200: Sets the baud rate for reliable communication.

  • -w YourSketchName.ino.bin: Specifies the binary file to write.

  • -v: Verifies the flash after writing.

  • -g 0x0: Starts execution from the beginning of the flash memory after programming.

  • /dev/ttyUSB0: The serial port of your FTDI adapter.

Step 6: Run the Application

Disconnect the power.

Set the BOOT0 jumper back to the '0' position.

Reconnect power or press the RESET button.

The board will now boot into your application. You can open the Arduino IDE's Serial Monitor at 9600 baud to see the debug output.

Code Explanation

  • Configuration (#define): All hardware pins, timing delays, and operational thresholds are defined at the top of the file for easy configuration.

  • setup(): This function runs once on startup. It initializes the serial ports for debugging, starts the DHT and DS18B20 sensors, and crucially, initializes the SIM800L module with a series of AT commands to prepare it for sending SMS. It also reads the last known smsCounter value from the EEPROM.

  • loop(): This is the main operational cycle.

    • It first ensures the GSM module is initialized and ready.

    • It reads the current temperature and humidity from both sensors.

    • The readings are added to summing variables (dhtHumSum, dhtTempSum, etc.).

    • A counter (smsCounter) is incremented and saved to the EEPROM.

    • It checks if smsCounter has reached the SMS_SEND_THRESHOLD (e.g., 12).

    • If the threshold is met, it calculates the averages, fetches a network timestamp, formats the SMS message, and sends it to all phone numbers in the phoneNumbers array.

    • Finally, it resets the summing variables and the smsCounter back to zero and waits for 5 minutes (MAIN_LOOP_CYCLE_DELAY) before starting the next cycle.

  • GSM Helper Functions: Functions like sendSMS(), getGsmTimestamp(), and handleSim800lInput() abstract the complexity of communicating with the SIM800L module.

DIP Switch Configuration

The system uses a 5-position DIP switch to enable/disable individual sensors and MQTT publishing:

  • DIP Switch 1 (PC13): DHT11 Temperature & Humidity Sensor
  • DIP Switch 2 (PC14): DS18B20 Waterproof Temperature Sensor
  • DIP Switch 3 (PC15): FC-28 Soil Moisture Sensor
  • DIP Switch 4 (PB12): MQ2 Gas Sensor
  • DIP Switch 5 (PB13): MQTT Publishing to test.mosquitto.org

Switch Logic:

  • Switch DOWN (pulled to ground) = Feature ENABLED
  • Switch UP (pulled high) = Feature DISABLED

Important: The system reads DIP switches only during startup/boot. To change sensor or MQTT configuration, modify the DIP switches and restart the system. Only enabled sensors are read and included in SMS reports. If MQTT is enabled, data will be published to test.mosquitto.org after SMS transmission.

SMS Commands

The system supports remote configuration and monitoring via SMS commands. Send these commands to the SIM card phone number:

Configuration Commands

  • NUMSETA +1234567890: Set phone number A
  • NUMSETB +1234567890: Set phone number B
  • NUMSETC +1234567890: Set phone number C
  • SETID 12345: Set customer ID (max 9 characters)

Status Commands

  • STATUS: Get current configuration, enabled sensors, and MQTT status
  • TEST: Simple connectivity test
  • SENSOR: Get current real-time sensor readings from enabled sensors
  • MQTT: Test MQTT publishing (if MQTT enabled)

Example SMS Responses

  • STATUS: ID:12345 A:+94719593248 B:+94719751003 C:+94768378406 Sensors: DHT DS18B20 SOIL MQTT
  • SENSOR: ID:12345 Current: DHT H:65.2% T:28.4C; DS18B20:27.8C; Soil:45.3%;
  • MQTT: ID:12345 MQTT test publish initiated

MQTT Integration

When the MQTT DIP switch is enabled (DIP Switch 5), the system will:

  1. Automatic Publishing: After sending SMS data, automatically publish sensor data to MQTT
  2. MQTT Broker: Uses test.mosquitto.org on port 1883 (public test broker)
  3. Topic Structure: sensors/stm32/{customer_id}
  4. Data Format: JSON payload with sensor readings and metadata
  5. Manual Testing: Use MQTT SMS command to test publishing

MQTT Data Example

{
  "customer_id": "FARM01",
  "timestamp": "2025-08-03 14:30:15",
  "dht_humidity": 65.2,
  "dht_temperature": 28.4,
  "ds18b20_temperature": 27.8,
  "soil_moisture": 45.3,
  "gas_level": 12.1,
  "reading_count": 12
}

All configurations are saved to EEPROM and persist across power cycles.

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