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MMC (micro SD) HAT for Raspberry Pi

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This HAT adds a second micro SD socket to your Raspberry Pi.

Being able to plug in a second micro SD card opens up a variety of interesting possibilities, such as:

  • A micro SD card reader! Write new images, repair or modify existing Raspberry Pi installations with ease.
  • Additional storage - mount as your home directory, for general storage or backups.
  • RAID1 on the root (/) partition for added reliability.
  • Connector for Controller Serial Console using our USB Serial Adaptor.

Please note: MMC HAT is only supported on Raspberry Pi OS at present


Compatible with

  • Raspberry Pi A+
  • Raspberry PI B+
  • Raspberry Pi Zero & Zero W1 (with headers)
  • Raspberry 2B
  • Raspberry Pi 3B1 & 3B+1
  • Raspberry Pi 4B

1When used on a Raspberry Pi Zero W, 3B or 3B+ the on-board WiFi is disabled as it is on the SDIO interface used by the MMC HAT

The Raspberry Pi 4 has three SD controllers so you can use onboard SD, WiFi and the MMC HAT (SD) at the same time on the Pi4!

When using a Raspberry Pi 4 please add the following three lines to the TOP of the config.txt file in the boot directory.





With the standard SD clock speed a micro SD card in the MMC HAT (/dev/mmcblk2) performs at similar speeds to the onboard micro SD card (/dev/mmcblk0).


  • 1 x MMC HAT
  • 4 x 12mm M2.5 standoff
  • 8 x 6mm M2.5 screw
  • 4 x stick on foot