External SD card using Adafruit breakout





  • Looking at the datasheet for the level shifter there (CD74HC4050), it says you can power it with 2V to 6V.

    At 4.5V power, the minimum voltage required for a logic high is 3.15V. That feels way too close to 3.3V if you want reliability at different temperatures, system loads, and cable lengths. At 5V or even 6V, that 3.15V becomes even higher, maybe even over 3.3V, making it impossible to be used. At 6V power, that minimum is 4.2V!

    For the transistors inside this chip, the rule is that the minimum logic high input level is about 70% of the input power.

    But since the Duet has 3.3V power, if you powered the CD74HC4050 with 3.3V, that number becomes much lower. 70% of 3.3V is about 2.3V. I think this could be reliable.

    So if you already purchased it, try it out, it should work, but only if you connect the power input pin to 3.3V, NOT 5V.

    It's easy to bypass the level shifter if you need to. Desolder it first (use a hot air gun, or cut each leg individually with a knife), then simply use 30 gauge wires to bridge each input to the corresponding output.

    My own build uses a SparkFun SD card breakout that does not have any level shifter. It works great. I like full sized SD way more.

    https://www.sparkfun.com/products/12941

    If you want something dirt cheap, then just get a plastic microSD to SD adapter, and solder wires to it.


  • administrators

    @frank26080115 said in External SD card using Adafruit breakout:

    If you want something dirt cheap, then just get a plastic microSD to SD adapter, and solder wires to it.

    I don't advise that because those adapters tend to damage the micro SD card on the Duet. The Sparkfun SD card socket or similar without level shifters would be preferable.



  • @frank26080115 said in External SD card using Adafruit breakout:

    My own build uses a SparkFun SD card breakout that does not have any level shifter. It works great. I like full sized SD way more.

    https://www.sparkfun.com/products/12941

    I, too, prefer SD cards over uSD. Are you connecting to the conn_sd port on the Duet board, and what is the cable length limit? Thanks!


  • administrators

    The vast majority of Duet users upload files to the SD card from Duet Web Control, or over the network directly from the slicer. So they rarely need to remove the SD card, and a full size one would have no advantage. OTOH the Duet would have to be larger to accommodate one.



  • @mrehorstdmd said in External SD card using Adafruit breakout:

    cable length limit

    I gathered information from https://duet3d.dozuki.com/Wiki/PanelDue and it says:

    Connections to the onboard micro SD card socket as well as the PanelDue serial and power connections are all available via a 10-way ribbon cable. A 300mm long ribbon cable is the maximum recommended length.

    Personally? My ribbon cable is only about 5 inches, so about 127mm

    @dc42 said in External SD card using Adafruit breakout:

    I don't advise that because those adapters tend to damage the micro SD card on the Duet.

    Huh? Are we talking about the same thing? I'm talking about doing this

    alt text

    I don't think this has any risk of damaging anything expensive


  • administrators

    No, I was talking about full size SD card sockets that have a micro SD size plug on them.



  • @frank26080115 thanks so much for the detailed feedback - I really appreciate it. I'd only looked at the adafruit one as a known brand, on a site I order from regularly. Knowing theres a sparkfun version that I can buy that'll work without any hassle, and with full size SD cards is spot on - so I went with that one instead! Thanks for the recommendation 🙂

    And the other conversation has been informative too - I use one of those full size SD to microSD adaptors with another printer, and while touch wood I haven't had any issues with it, I won't let it anywhere near a duet now lol.

    So the replies are much appreciated, thanks all



  • I will add my 2 cents on the matter.

    I have successfully connected this kind of an SD slot board to the DUET 2 "CONN_SD" port

    The board has both 3.3V and 5V input, I went with 3.3V. Connecting it is really rather easy, get the DUET pinout diagram and make connections from DUET "CONN_SD" to the board, GND to GND, CS to CS, MISO to MISO and so on.

    I used an ethernet solid core cable and in total its maybe around 1m long. So far I have two over 8h long prints behind me and so far with no issues.


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