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I will be inserting something else (video adapter board) into the micro-sd card slot. The device will operate for output only, and there will be no feedback on what actually is inserted into the micro-sd card slot.

There's of course probability that someone will insert real sd-card into the slot when it is not expected to be there, and I am afraid sd-card may not like it (a lot). The first idea I have got is to detect real sd-card using its socket's card detect mechanism. But for this to work my video adapter board must not close the slot's internal sd-card detect switch.

Can't find any prior art for it, and looking for advice, in particular information on why it is not possible or not (mechanically) recommended. I understand that different manufacturers' micro-sd card slot may be different, and of course can look for specific datasheets for the info, but I do not think will be able to devise correct adapter board shape using these datasheets.

Therefore looking for generic informed advice of the people who were designing or maintaining the micro-sd card sockets.

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  • \$\begingroup\$ Could you be more specific as to why you think a real SD-Card might object to being put into this non-standard slot? \$\endgroup\$
    – brhans
    Commented Jan 31, 2023 at 21:26
  • \$\begingroup\$ Because SPI CS, CLK and IOs will be used completely differently. CLK will remain CLK (but at higher speeds than card supports), but CS and will convey color data, and who knows how card will treat this arbitrary color data. IO lines will always be output. I would try preventing related issues completely at the design stage than instruct users to follow some rules and then get reports about damaged cards or data on them. \$\endgroup\$
    – Anonymous
    Commented Jan 31, 2023 at 22:07
  • \$\begingroup\$ Have you considered designing your video adapter to conform to something like the SDIO Camera "Standard Function" such that it uses the SD-Card/SDIO lines an a standard-compliant way? \$\endgroup\$
    – brhans
    Commented Jan 31, 2023 at 22:27
  • \$\begingroup\$ No, but I think I get what you mean - having similar frames over SPI supporting custom device. Color information is 15 bits, and I need to convey 15 bits with frequency of 25 MHz, giving cumulative 100 MHz operation on data only without framing overhead. I am afraid 100 MHz is max current hardware design will tolerate. Next, the complexity - simpler protocol makes receiving end implementation simpler (less complex and less power consumed). \$\endgroup\$
    – Anonymous
    Commented Jan 31, 2023 at 22:37

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My recommendation here is, since it appears that your intended use for the "plug in" is exclusive for the video adapter, that rather than overloading the uSD Card slot type connector for a non-intended usage is that you think hard about not doing this. Instead devise some custom solution for connection that is unique to your application and avoid the issues raised in your question.

Kludging things together almost always leads to hacks on top of hacks.

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  • \$\begingroup\$ It is used for uSD card access within another FPGA image. And it is the only electrical interface I can connect to the device with and try getting video through. That's why so many complications... \$\endgroup\$
    – Anonymous
    Commented Jan 31, 2023 at 19:53
  • \$\begingroup\$ The logical and signal connections into an FPGA can be sourced via many types of electrical connection options and not just a uSD card slot connector! \$\endgroup\$
    – Michael Karas
    Commented Jan 31, 2023 at 20:11
  • \$\begingroup\$ But only uSD card slot is looking out of the device's casing. Soldering to the product inside it is even worse idea. rs.gr8bit.ru/Documentation/GR8NET-manual.pdf \$\endgroup\$
    – Anonymous
    Commented Jan 31, 2023 at 20:14

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