Data Logger Module(SD card)

The SparkFun OpenLog is one of the most popular and well-loved open-source serial data loggers ever created — a beautifully simple yet powerful module that does one job exceptionally well: capturing serial UART data and writing it to a microSD card. If you've ever needed to log GPS coordinates, sensor readings, debugging output, or any other serial stream over hours, days, or months, OpenLog is the go-to solution for makers, students, engineers, and researchers worldwide.

The philosophy behind OpenLog is "it just works". Connect three wires — VCC, GND, and TX (from your microcontroller's TX to OpenLog's RX) — power it up, and it immediately starts logging incoming serial data at 9600 bps by default. The data is written to a microSD card formatted as FAT16 or FAT32, supporting cards up to 16GB (tested) — providing virtually unlimited storage for typical sensor logging applications.

OpenLog is built around an Arduino-compatible ATmega328 microcontroller, which means you can reprogram the firmware using the Arduino IDE to customize its behavior or add new features. The original firmware is based on Bill Greiman's well-known sdfatlib (now SdFat) library, which provides robust and efficient FAT filesystem support with low memory overhead — perfect for embedded data logging.

Three Operating Modes

OpenLog offers three flexible operating modes to fit different logging needs:

1. NewLog Mode (Default) — Every time OpenLog powers up, it creates a brand new log file (LOG00000.TXT, LOG00001.TXT, etc.) and immediately starts logging. Ideal for projects where you want separate files per session (e.g., each car trip, each experiment run).
2. SeqLog Mode — Appends all data to a single file called SeqLog.txt every time it powers up. Perfect for continuous, long-term logging where you want one big file to analyze.
3. Command Mode — Boots into an interactive command-line interface where you can list files, create directories, read files, delete files, and configure settings. Useful for debugging, file management, and direct interaction.

Easy Configuration

OpenLog is configured via a simple config.txt file that you can edit directly on a computer (just plug the microSD card into your PC). You can change:

• Baud rate (from 2400 to 115200 bps)
• Operating mode (NewLog, SeqLog, Command)
• System name and identifiers
• Verbose / silent operation for messages
• Echo settings for command mode

This means you can fine-tune OpenLog for your specific project without recompiling firmware — just edit a text file and reboot.

Compact and Power-Efficient

OpenLog is impressively small at just 0.16 x 0.6 x 0.75 inches (4 x 15 x 19 mm), making it easy to embed in compact projects, drones, RC vehicles, wearables, and remote sensor stations. It accepts a wide input voltage range from 3.3V to 12V, allowing it to run from batteries, Arduino 5V rails, USB power, or vehicle power systems. Power consumption is also extremely low — just 2 mA at idle and 6 mA at maximum recording rate — perfect for battery-powered, long-duration logging projects.

Visual Feedback

Two onboard status LEDs provide instant visual confirmation of operation:

• STAT1 LED — Indicates that data is being received
• STAT2 LED — Indicates SD card write activity

Open-Source Goodness

OpenLog is fully open-source hardware and firmware:

• Schematics, PCB layout, and firmware all licensed under the CC-SA v3 license
• All design files available on GitHub (github.com/sparkfun/OpenLog)
• Active community contributing improvements, bug fixes, and new firmware variants
• New firmware versions support Arduino 1.0+ and higher baud rates
• Custom firmware variants exist for specialized use cases (faster baud, different file naming, etc.)

This open philosophy makes OpenLog ideal for educational use, scientific research where reproducibility matters, and commercial products that need a customizable logging solution.

Common Use Cases

OpenLog excels in scenarios like:

• GPS data logging — record NMEA strings from GPS modules to SD card for later mapping
• Long-term environmental monitoring — temperature, humidity, pressure, light data
• Drone and RC vehicle telemetry — record flight data for post-flight analysis
• Automotive data logging — OBD-II, sensor, or accelerometer data while driving
• Solar / wind / battery system monitoring — track performance over weeks
• Robotics debugging — log sensor and actuator data to diagnose issues
• Scientific experiments — capture serial data from research instruments
• Black box recorders — store mission-critical data for engineering analysis
• IoT sensor stations — local backup of cloud-uploaded data
• Educational STEM projects — first introduction to data logging

The combination of simplicity, reliability, low power, small size, and open-source design makes OpenLog one of the most versatile and time-tested data logging solutions in the maker community.

Specifications

General

• Type: Open-Source Serial-to-SD Data Logger
• Microcontroller: Atmel ATmega328 (Arduino-compatible)
• Storage: microSD card (FAT16 / FAT32)
• Maximum Card Size Tested: 16 GB
• Input Voltage: 3.3V – 12V DC
• Idle Current: 2 mA
• Max Recording Current: 6 mA
• Dimensions: 4 x 15 x 19 mm (0.16" x 0.6" x 0.75")

Communication

• Default Baud Rate: 9600 bps
• Configurable Baud Rates: 2400, 4800, 9600, 19200, 38400, 57600, 115200 bps
• Interface: Serial UART
• Minimum Connections: VCC, GND, RX-I (3 wires)

Operating Modes

• NewLog Mode: New file created every power cycle (LOG#####.TXT)
• SeqLog Mode: Append to single file (SeqLog.txt) on every boot
• Command Mode: Interactive command-line interface for file management

Indicators

• STAT1 LED: RX activity (data being received)
• STAT2 LED: SD write activity

Pinout (Typical)

Applications

• GPS data logging — long-term position tracking with NMEA strings
• Drone and quadcopter telemetry recording
• RC vehicle performance logging
• Automotive data logging — OBD-II, custom CAN, or sensor data
• Solar panel and wind turbine monitoring
• Battery system performance tracking
• Environmental sensor stations — temperature, humidity, air quality
• Weather station data logging
• Smart agriculture — soil moisture, irrigation, greenhouse data
• Robotics debugging and flight data recording
• Scientific experiment data capture
• High-altitude balloon and rocketry telemetry
• Marine and underwater sensor logging
• Wildlife monitoring stations
• Industrial sensor logging for predictive maintenance
• Black box recorders for engineering and product testing
• Long-term IoT data backup
• Educational STEM and university research projects
• Hobbyist data logging for any serial-output device
• Astrophotography session logging
• Off-grid energy monitoring for cabins and remote installations