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My goal is to make a MicroSD to USB adapter myself.

With this question, I saw that I can use a USB2240 controller chip to connect my µSD card to my computer.

In this video, he is using a 1701 ic which seems to be a voltage regulator and everything seems to work fine.

In that case, what are the benefits of a controller chip over just a simple voltage regulator?

Also, in the previous Electrical Engineering Stack Exchange question, the OP put a link about M-Stack, do I need to install it on the USB2240 controller chip to make it work and what is it exactly?

Sorry these questions might be stupid, I am still a beginner. Thanks.

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    \$\begingroup\$ Whatever that chip is, it isn't just a voltage regulator. \$\endgroup\$
    – Ron Beyer
    Commented Jun 22, 2020 at 18:32
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    \$\begingroup\$ The benefit of using a USB controller is that it lets you connect over USB. Without one, you can draw power from a USB port, but not access data. \$\endgroup\$
    – user1850479
    Commented Jun 22, 2020 at 18:54
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    \$\begingroup\$ @ufjyxnm7ux If USB works then he has a USB controller. Post a datasheet for the chips you're asking about. \$\endgroup\$
    – user1850479
    Commented Jun 22, 2020 at 22:30
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    \$\begingroup\$ So desolder the connector from a commercial one, though as the smaller ones put the card practically inside the connector that's not going to help much. Your question makes it clear you are not ready to tackle this project. \$\endgroup\$
    – Chris Stratton
    Commented Jun 23, 2020 at 1:36
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    \$\begingroup\$ @ufjyxnm7ux it's not that all projects are pointless, it's that a project that is little more than a fixed function IC generally best sourced as a finished product is pointless. Something that was a USB gizmo that needed MCU firmware could be a quite rewarding project, but that's not what an SD->USB adapter is. Such a device is a pointless project because you cannot realistically build a better one than you can buy, other projects are not. Developing a sense of where it is vs isn't worth putting effort is as important a part of it as any other. \$\endgroup\$
    – Chris Stratton
    Commented Jun 23, 2020 at 2:11

1 Answer 1

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Before embarking on a project like uSD interface over USB, you need to understand/appreciate few things.

  1. USB is a complex protocol, which has no direct relationship with multitude of SD cards protocols.
  2. The 1701 IC is apparently a bridge between USB (likely FS, or maybe HS) protocol and uSD card. Looking at their "schematics", the IC uses the simplest initial SPI-like protocol to access uSD data.
  3. To get access to uSD, the IC bridge implements complex data structures that represents USB Mass Storage Class (MSC). Without the MSC your PC will not understand data/control formats.
  4. To bridge a uSD to MSC interface, the IC must first initialize the SD interface, and then evaluate uSD card capability and file structure. This requires lengthy serial data transfers on uSD side, and analysis of card responses. Remember, there are many types of uSD cards, of various sizes and write structures, and one never knows what kind of card you will insert. So the IC bridge must be intelligent enough to recognize the particular card.
  5. All this functionality is hidden from you inside the IC, so there is not much you can learn, unless you put USB analyzer on USB end, and SD/MMC analyzer on the card's end.
  6. I know nothing about "AB701" IC, but if you try USB2240, you will need a 24MHz crystal, couple of capacitors, you can find reference design files on MCHP site.
  7. The USB2240 embeds a 8-bit microcontroller with advanced 80C51 architecture, which runs a code from internal flash memory, which is compiled from thousands of lines of C++ code, so the chip will discover identity of plugged uSD card, and built proper capability tables to report in accord with Mass Storage Class interface.
  8. As you now can see, the youtube video is highly misleading, by hiding all the above technicalities.
  9. You can certainly solder all 36 wires to the QFN36 IC with tiny 0.5 mm pitch, and, if done correctly, it might work. Better, you will need to design a PCB (say, using free tool from ExpressPCB), all in accord with manufacturer's recommendations, and you will have an interface to uSD card over USB port.

Good luck.

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  • \$\begingroup\$ Thank you for such a detailed answer and pointing where so much things. Thanks a lot. \$\endgroup\$
    – ufjyxnm7ux
    Commented Jun 24, 2020 at 16:09

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