OpenLog

That's really it! OpenLog firmware is open source and is based on Roland Riegel's FAT library. OpenLog currently supports FAT16 (upto 2GB microSD cards). We're working on FAT32 and would love your help!

All the design files (schematic, PCB layout, firmware) are open source released under the CC-SA v3 license and are available through GitHub.

Features:

Log to low-cost microSD cards up to 2GB
Simple command interface
Edit CONFIG.txt file from a computer to change baud rate and other system settings
Three modes:
- NewLog creates a new log every power up and immediately starts logging
- SeqLog appends a file called "SeqLog.txt" at every power up and immediately starts logging
- Command mode starts OpenLog at a command prompt at power up
Configurable baud rates (2400 to 115200bps)
Configure unit through config file or the menu system
Doesn't drop characters even at full-blast 57600bps
Power, ground, and RX-I are the minimum connections
Reprogrammable ATmega328 using the standard STK500 serial bootloader
Two LEDs indicate writing status
Input voltage from 3.3V to 12V
2mA idle, 6mA at maximum recording rate

Dimensions: 0.16 x 0.6 x 0.75" (4 x 15 x 19mm)

Documents:

Homepage
Example Arduino Sketch
Command Set
Datasheet
Datalogger comparison
Schematic
Latest main.hex firmware (right click and save-as)
How to upgrade the firmware
How do I use GitHub with Windows?

The OpenLog project is housed on GitHub! Please see the wiki for the most up-to-date firmware, feature requests, files, and datasheet specs.