From Mooshim Engineering Wiki
The Mooshimeter will accept a microSD card of the following specifications:
- Capacity <= 32GB
- SD or SDHC are accepted
- SDXC is not accepted
- Formatted with a FAT32 filesystem
- This is the default filesystem for almost all new microSD cards. You probably don't need to do anything to your card.
- If you do need to reformat the card, instructions can be found here