I think this may work, but I wanted a second opinion before I go off and buy all of the parts!

I am working on a data logger where it would be useful to use a second SD card (not the OS card) to periodically transfer data to. It will also have a minimal user interface, probably just a simple LCD display and a few buttons.

I want to be able to press a button to trigger a "Download data to SD card" function.

If I mount the reader to the pi, when writing do I address the reader or the card? So will it matter if, due to a misplaced/damaged card, I start using a different SD card?

  • you need to work out how to mount the "SD" card. There are some automount options to make life easier, in case you use a different SD card or even a different partition format. autofs - I answered something like a few days ago about MP3 playlists or something.
    – Piotr Kula
    Dec 1 '14 at 15:32

I would expect you to attach the SD card reader via USB. Then when you insert an SD card new device nodes would appear /dev/sdc/, /dev/sdc1 etc that you would then mount to a folder.

Once mounted just write to the folder with normal files/folders.

Unless you are talking about direct sector writing/streaming in which case I have no idea.

  • Thanks for your answer. So you think I would have to mount each SD card that would be inserted? That may be an issue.
    – Doragan
    Sep 2 '14 at 14:46
  • its something I always avoid on Linux based systems, I like having to mount each device before use and hate the Ubuntu auto mount system. There should be a way to nicely auto mount the cards even if you have to write a script file that just checks if the card is there and mounts it. The question then is how to know it is safe to remove the card.
    – rob
    Sep 3 '14 at 16:09

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