The Duets have a built-in micro SDHC card socket. A compatible SD card is supplied with the Duet.

In normal use, you should never need to remove the SD card from its socket. You can transfer files to/from the SD card over the web interface.

Caution! Do not use an SD extender cable. Such cables do not generally work well at the high SD card transfer speeds used by the Duet. Additionally, some types of SD card extender cable have been found to damage the SD card socket. Damage to the SD card socket from using an extender cable is not covered by the warranty.

If you need to reformat the micro SDHC card:

• If the capacity of the card is 4GB or lower, use FAT16 format
• If the capacity is more than 4GB (up to 32GB) then you will have to use FAT32 format
• All cards should be formatted with 512 byte sectors
• For best upload speed choose the largest cluster size available, which is normally 64kb for FAT16 and 32kb for FAT32
• Use the official SD Card formatting tool for best results: https://www.sdcard.org/downloads/formatt...

If you need to replace the micro SDHC card, we recommend you choose:

• a branded card with a speed rating of Class 4 or higher
• of up to 32GB capacity, formatted as above. RepRapFirmware does not support SD cards formatted in exFAT format.

It is possible to connect a second, low-speed SD card socket to the Duet - see Connecting an LCD control panel: Using the external SD card socket on the LCD panel

For information on the SD card structure see : Firmware Overview: SD Card Structure

Send M122 to the Duet and look for the 'SD Card' entries. A normal response should look like:

SD card 0 detected, interface speed: 20.0MBytes/sec
SD card longest block write time: 5.1ms, max retries 0

If it responds with "SD card detected" in M122, it indicates that the Card Detect pin of the SD card is working (this is also the pin whose soldering causes the most trouble).

The interface speed in the same line gives an indication of whether the processor is able to communicate with the SD card at all. It should be 20Mbytes/sec on a Duet WiFi/Ethernet, 15Mbytes/sec on a Duet Maestro, and 25Mbytes/sec on Duet 3 in standalone mode. Other numbers, eg 12Mbytes/sec, are odd and suggest an issue with the SD card. If the socket or processor is faulty but the card is detected, it usually drops to 0.2Mbytes/sec.