Wednesday 23 September 2015

FT2232H stick & 0gb microSD cards

Not particularly interesting, but if you're at all curious about what's accepted for PCB manufacture in terms of multiple boards separated by anything other than silkscreen (it's not possible to get a straight answer from anyone - I tried!) then this had no problems whatsoever:

Although the other bits don't really count as "boards", and of course YMMV.

It's a tiny FT2232H JTAG/UART adapter using the QFN package variant. The schematic is just the reference design from the datasheet like the rest. The GPIO reset pins are "Floss JTAG" compatible IIRC, although probably not required. The board size was chosen to fit those Chinese metal flash drive casings

I also screwed up (finally)! I completely missed a connection to VREG_IN, so it's got a microscopic bodge wire:

The fake micro sd cards worked well - 0.8mm being the upper limit from the specs so might be tight in some sockets without sanding it down. One unavoidable problem is there is 1 corner that a 0.8mm milling bit cannot quite cut far enough (because it's round...) but it doesn't seem to make any actual difference in use, and nothing that couldn't be fixed with a small file.

Allwinner Axx SoCs have JTAG and UART mux'ed on the SDIO pins, so these adapters are meant for debugging "China-pads". The dummy card and eMCP test were really just to fill space :) I would not recommend trying to get a 0.5mm pitch BGA using NSMD pads on a cheap PCB - it was that badly aligned it wasn't usable. Having said that you also wouldn't have space to route more than a few traces anyway... 0.8mm isn't possible if you intend it to pass a DRC :(


  1. would you please share your microsd pcb design?

    1. Sure - here you go
      It's in Eagle lbr format, hope that's OK.

    2. Thank you so much,
      you've said that it might be tight in some sockets with 0.8mm PCB thickness, does it need to sanding each PCB? isn't it better to use 0.5mm PCB?

    3. No, it fits OK in everything I have tried it in. 0.5mm is below the minimum so it would probably not make good contact with the pins.

      Manufacturers specs (e.g. ) usually say 0.7+/-0.05, so 0.65-0.75mm. 0.8 is "close enough"!

    4. Thanks @stevenhoneyman,
      it works fine, and we solved our ESD problem by this board.

  2. Hi,

    Would it be possible to share the eagle file for the MicroSD design again as the previous link is now dead? Much appreciated

    1. Hi,

      Sure - here you go:

      The link broke when dropbox removed the default "public" folder.