Complete temperature and humidity data acquisition and logging system using ESP8266, DHT22 sensor and SSD1306 OLED display, with WiFi connectivity, NTP synchronization, MQTT publishing and HTTP server.
- Data Acquisition: Periodic temperature and humidity readings with DHT22 sensor
- OLED Display: Real-time data visualization on SSD1306 128x64 display (I2C) with optional power saving mode
- WiFi Connectivity: Automatic connection and smart reconnection
- Time Synchronization: NTP synchronized with Brazilian servers
- MQTT Publishing: Data transmission to MQTT broker with batching and retry
- HTTP Server: Web interface for monitoring
- SPIFFS Storage: Local backup of measurements when offline
- Modular Architecture: Refactored code with clear separation of concerns
- FreeRTOS: Multitasking system with optimized priorities
- Microcontroller: ESP8266 NodeMCU (Ideaspark ESP8266MOD)
- Sensor: DHT22 (temperature and humidity)
- Display: Integrated OLED SSD1306 128x64 (I2C)
- I2C Connections:
- SDA: GPIO12
- SCL: GPIO14
- OLED Address: 0x3C
- DHT22 Sensor: GPIO4
esp8266_datalogger_dth22_ssd1306/
├── main/
│ ├── main.c # Application entry point
│ ├── config.h # System configuration
│ ├── types.h # Data type definitions
│ ├── globals.h/c # Shared global variables
│ ├── wifi_manager.h/c # WiFi management
│ ├── ntp_manager.h/c # NTP synchronization
│ ├── mqtt_manager.h/c # MQTT client
│ ├── http_server.h/c # HTTP server
│ ├── measurement.h/c # DHT22 data acquisition
│ ├── oled_display.h/c # OLED display control
│ ├── spiffs_manager.h/c # File system management
│ ├── dns_manager.h/c # DNS cache for MQTT broker
│ ├── system_status.h/c # System monitoring
│ └── time_cache.h/c # NTP timestamp cache
├── components/
│ └── ssd1306/ # OLED display driver
├── CMakeLists.txt
├── partitions.csv
└── sdkconfig
- ESP8266_RTOS_SDK
- CMake 3.5+
- Xtensa Toolchain
sdkconfig file. This file MUST NOT be committed to Git as it contains passwords and sensitive information.
idf.py menuconfigNavigate to "Datalogger Config" and configure:
- WiFi SSID: WiFi network name
- WiFi Password: Network password
- MQTT Broker: MQTT broker address (e.g., mqtt://broker.hivemq.com:1883)
- MQTT Username: MQTT username
- MQTT Password: MQTT password
- MQTT Topic Data: Topic for data publishing (e.g., sensors/temperature/data)
- MQTT Topic Status: Topic for system status (e.g., sensors/temperature/status)
- Sensor ID: Unique sensor identifier (e.g., ESP8266-001)
- Measurement Interval: Interval between measurements in ms (e.g., 30000 = 30s)
- Enable OLED Display: Enable/disable the OLED display (disable to save power)
- Copy the example file:
cp sdkconfig.defaults sdkconfig.defaults.local-
Edit
sdkconfig.defaults.localwith your credentials (this file is gitignored) -
Run build normally:
idf.py buildBefore pushing to GitHub, always verify:
# Check if sdkconfig is not being tracked
git status | grep sdkconfig
# If it appears, remove from staging
git reset HEAD sdkconfig sdkconfig.old
# Verify .gitignore
cat .gitignore | grep sdkconfig# Configure
idf.py menuconfig
# Build
idf.py build
# Flash
idf.py -p /dev/ttyUSB0 flash
# Monitor
idf.py -p /dev/ttyUSB0 monitorThe system operates with multiple tasks with optimized priorities:
| Task | Priority | Function |
|---|---|---|
| oled_display | 7 | OLED display updates |
| wifi_monitor | 6 | WiFi connection monitoring |
| ntp_sync | 5 | NTP synchronization |
| mqtt_monitor | 4 | MQTT monitoring |
| measurement | 3 | DHT22 data acquisition |
| http_server | 2 | HTTP server |
| system_status | 1 | System status |
- Batching: Message grouping to optimize transmission
- Retry: Automatic resend on failure
- Backlog: SPIFFS storage when offline
- Keep-alive: Periodic heartbeat to maintain connection
Displays in real-time:
- Current temperature and humidity
- WiFi connection status
- Local timestamp (GMT configurable)
- User-configurable string
- Number of messages sent/stored
- Special icon that blinks after each measurement
Power Saving Mode: The OLED display can be completely disabled via Kconfig to reduce power consumption. When disabled, the display is cleared and turned off during system initialization, saving energy in battery-powered deployments.
- Ring buffer storage (configurable, default: 1000 measurements)
- Automatic synchronization when reconnecting to MQTT
- Data persistence during power outages
- Alert when buffer reaches 80% capacity
{
"sensor_id": "ESP8266-001",
"timestamp": 1696348800,
"temperature": 25.3,
"humidity": 62.5
}The system provides detailed logs via UART:
idf.py monitorAvailable log tags:
MAIN- Main initializationWIFI- WiFi eventsNTP- Time synchronizationMQTT- MQTT publishing and statusMEASUREMENT- Sensor readingsOLED- Display updatesSPIFFS- File system operationsHTTP- HTTP requests
The HTTP server exposes the following endpoints:
GET /- Main page with system statusGET /data- Latest measurements (JSON)GET /status- Complete system status (JSON)
- Check SSID and password in menuconfig
- Verify WiFi signal and compatibility (2.4GHz only)
- Check broker connectivity
- Validate MQTT credentials
- Verify configured topics
- Check I2C connections (SDA=GPIO12, SCL=GPIO14)
- Confirm display I2C address (default: 0x3C)
- Verify "Enable OLED Display" is enabled in menuconfig
- Check connection on GPIO4
- Wait 2 seconds after power-on
- Check sensor power supply (3.3V-5V)
This project is licensed under the terms of the MIT License.
elbastos(at)gmail.com
Developed for environmental monitoring IoT applications.
Firmware Version: 1.0