SparkFun Qwiic OpenLog

The SparkFun Qwiic OpenLog is the smarter and better looking cousin to the extremely popular OpenLog but now we've ported the original serial based interface to I2C! Thanks to the added Qwiic connectors, you can daisy chain multiple I2C devices and log them all without taking up your serial port. The Qwiic OpenLog can store, or "log", huge amounts of serial data and act as a black box of sorts to store all the data that your project generates, for scientific or debugging purposes. Utilizing our handy Qwiic system, no soldering is required to connect it to the rest of your system. However, we still have broken out 0.1"-spaced pins in case you prefer to use a breadboard.

Like its predecessor, the SparkFun Qwiic OpenLog runs off of an onboard ATmega328, running at 16MHz thanks to the onboard resonator. The ATmega328 has been sure to feature the Optiboot bootloader loaded, which allows the OpenLog to be compatible with the “Arduino Uno” board setting in the Arduino IDE. It is important to be aware that the Qwiic OpenLog draws approximately 2mA-6mA in idle (nothing to record) mode, however, during a full record the OpenLog can draw 20mA to 23mA depending on the microSD card being used.

The Qwiic OpenLog also supports clock stretching, which means it performs even better than the original and will record data up to 20,000 bytes per second at 400kHz. As the receive buffer fills up this OpenLog will hold the clock line, letting the master know that it is busy. Once the Qwiic OpenLog is finished with a task, it releases the clock thus allowing the data to continue flowing without corruption.

Note: The SparkFun Qwiic OpenLog supports 64MB to 32GB microSD cards in both FAT16 and FAT32 formats.


The SparkFun Qwiic Connect System is an ecosystem of I2C sensors, actuators, shields and cables that make prototyping faster and less prone to error. All Qwiic-enabled boards use a common 1mm pitch, 4-pin JST connector. This reduces the amount of required PCB space, and polarized connections mean you can’t hook it up wrong.


  • Continuous data logging at 20,000 bytes per second without corruption
  • Compatible with high speed 400kHz I2C
  • Compatible with 64MB to 32GB microSD cards (FAT16 or FAT32)
  • Preloaded Uno bootloader so upgrading the firmware is as easy as loading a new sketch
  • Valid I2C Addresses: 0x08 to 0x77
  • 2x Qwiic Connectors
  • Example 1 - Writing to a log
  • Example 2 - Creating and appending a file
  • Example 3 - Creating a new empty file
  • Example 4 - Reading the size of a file
  • Example 5 - Read the contents of a file
  • Example 6 - Make a directory
  • Example 7 - Read contents of a directory
  • Example 8 - Remove a file and directory
  • Example 9 - Read firmware version
  • Example 10 - Check status
  • Example 11 - Change I2C address of OpenLog
  • Example 12 - Fast recording and benchmarking

These examples are included when you install the Qwiic OpenLog library.

SparkFun Qwiic OpenLog Product Help and Resources

Qwiic OpenLog Hookup Guide

February 7, 2019

The updated Qwiic version of the OpenLog Hookup Guide

Choosing an Arduino for Your Project

December 11, 2017

Examining the diverse world of Arduino boards and understanding the differences between them before choosing one for a project.

Core Skill: Programming

If a board needs code or communicates somehow, you're going to need to know how to program or interface with it. The programming skill is all about communication and code.

2 Programming

Skill Level: Rookie - You will need a better fundamental understand of what code is, and how it works. You will be using beginner-level software and development tools like Arduino. You will be dealing directly with code, but numerous examples and libraries are available. Sensors or shields will communicate with serial or TTL.
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Core Skill: Electrical Prototyping

If it requires power, you need to know how much, what all the pins do, and how to hook it up. You may need to reference datasheets, schematics, and know the ins and outs of electronics.

2 Electrical Prototyping

Skill Level: Rookie - You may be required to know a bit more about the component, such as orientation, or how to hook it up, in addition to power requirements. You will need to understand polarized components.
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