ESP32-S3 Differential Pressure Datalogger

This project is a datalogger built on the ESP32-S3 platform using the ESP-IDF framework. It's designed to read environmental data from a BMP280 sensor, display it on an OLED screen with a menu-driven interface, and log the data to an SD card. The system uses a DS3231 Real-Time Clock (RTC) for accurate timestamping and exposes the SD card as a USB Mass Storage Device for easy data access.

Please refer to the following main guides for usage guidance and documentation:

• User Interface Guide: A complete guide to the on-screen menu system and controls.
• Web UI Guide: Instructions for using the web interface to manage files.
• Software Architecture: An in-depth look at the software design, tasks, and communication mechanisms.
• Board Design: Details on the custom PCB, hardware components, and pinout.

Overview

Key Features

• Sensor Datalogging: Periodically reads:
  • Temperature and atmospheric pressure from a BMP280 sensor.
  • Differential pressure from an Omron D6F-PH sensor.
  • LiPo battery voltage and percentage.
  • Device uptime in seconds.
• Dual-Mode Data Smoothing: Configurable Kalman filtering is applied to all sensor readings. The system uses two distinct sets of filter parameters for "Normal" and "High-Frequency" logging modes. All parameters (kf_*_q, kf_*_r, kf_*_q_hf, kf_*_r_hf) can be customized in config.ini. If high-frequency (_hf) parameters are omitted, the system automatically calculates sensible defaults based on the normal-frequency values.
• SD Card Storage: Logs sensor data to CSV files on an SD card, with support for file rotation based on size (1MB limit, approx. 2 weeks of recording at 1 point per minute).
• Real-Time Clock (RTC): Utilizes a DS3231 RTC for accurate timestamps. The system can synchronize its time from the RTC on startup.
• OLED Display & UI: Features a menu-driven user interface on an OLED display, controlled by a rotary encoder with a push-button. The UI displays:
  • Real-time sensor data (temperature, pressure, differential pressure, battery status).
  • Current local timestamp (CET/CEST).
  • SD card write status.
  • Persistent status icons for battery level, charging status, and SD card write errors.
  • A settings menu to manage the RTC, SD card, view configuration, and display a QR code linking to the project repository.
• NTP Time Sync: Can synchronize the RTC with an NTP server over Wi-Fi.
• Web Server: Can start a web server to allow downloading and previewing logged data files directly from a web browser.
• Multiple Sampling Modes: Supports "Normal", "High Frequency", and "Paused" logging modes, selectable via the UI.
• Robust Power Management: Implements a command-driven deep sleep cycle to conserve battery. The datalogger task explicitly signals when it's safe to sleep, preventing race conditions and ensuring data integrity. The device wakes up on a timer for the next log or via user interaction. A safety threshold on battery voltage avoids data corruption when measured battery voltage is too low to guarantee stable power to the 3.3V rail.
• Web File Management: The web interface allows users to list, preview, download, and delete log files directly from the device.
• Exclusive File System Access: To prevent data corruption, the system ensures that only one component (Datalogger, Web Server, or USB Mass Storage) can access the SD card at a time. For example, starting the web server will pause the datalogger, and connecting the device to a PC will disable both the web server and the datalogger.
• Configuration & Persistence:
  • Permanent Settings: Key parameters like sleep intervals, Wi-Fi credentials, and sensor models can be configured via a config.ini file on the SD card. These settings are loaded into flash memory and persist across reboots.
  • Session Settings: UI-selected modes (like "High Frequency" or "Paused") are stored in RTC memory and persist through deep sleep cycles, but will be reset to their default values after a full power cycle or reboot.
• RTOS-based: Built on FreeRTOS, with separate tasks for data logging and UI rendering for a responsive and robust application.

Hardware Components

• Microcontroller: ESP32-S3
• Sensors:
  • BMP280: Barometric Pressure and Temperature (I2C)
  • Omron D6F-PH: Differential Pressure (I2C)
• Storage:
  • MicroSD Card Slot (SPI)
• Display:
  • OLED Display (I2C)
• User Input:
  • Rotary Encoder with Push-button
• Timekeeping:
  • DS3231 Real-Time Clock (I2C)
• Power:
  • LiPo Battery with a voltage divider for monitoring.

For more details on the custom PCB, see the board design documentation.

Hardware Notes

DS3231 RTC Configuration

Please be aware that this firmware automatically configures any connected DS3231 Real-Time Clock with specific default settings upon boot. These settings are optimized for low-power operation and resilience. For details on the exact register values being set, please refer to the readme.md file located in the lib/i2c_ds3231/ directory.

Usage

1. Configuration: Copy the config_sample.ini file to the root of your SD card and rename it to config.ini. Edit this file to set your Wi-Fi credentials, sensor model, and other parameters.
2. Operation: The device is controlled with the rotary encoder and its built-in push-button. For a detailed explanation of the menu system and on-screen information, please see the User Interface Guide.
3. Web Interface: When the web server is active, you can manage files from your browser. See the Web UI Guide for more details.

Software & Libraries

• Framework: ESP-IDF
• RTOS: FreeRTOS
• Component Management: Dependencies like qrcode and tinyusb are managed by the ESP-IDF Component Manager via the idf_component.yml file. The esp_tinyusb component for USB Mass Storage is enabled and configured directly through menuconfig, with settings reflected in the PlatformIO build profiles.
• Software Architecture: The project is built on a multi-tasking architecture using FreeRTOS. For a detailed explanation of the tasks and how they communicate, see the Software Architecture Guide.
• Custom Libraries (located in lib/): This project uses a modular structure with several custom libraries. Click on a library name to see its specific documentation.
  • config_manager: Handles loading configuration from an INI file.
  • i2c_bmp280: Driver for the BMP280 sensor.
  • i2c_d6fph: Driver for the Omron D6F-PH sensor.
  • i2c_ds3231: Driver for the DS3231 RTC.
  • i2c_oled: Driver for the OLED display.
  • kalman: kalman filter implementation.
  • lipo_battery: Logic for reading battery voltage.
  • ntp_client: Helper for synchronizing time from an NTP server.
  • rotary_encoder: Driver for the rotary encoder input.
  • spi_sdcard: High-level manager for SD card operations and USB MSC.
  • ui: Manages the complete user interface, menu, and pages. See the UI Guide.
  • web_server: Provides a web interface for downloading log files. See the Web UI Guide.
  • wifi_manager: Centralizes Wi-Fi connection and disconnection logic.