There are a lot of cheap MicroSD port extender flex ribbons from China. These things extend the MicroSD port quite a lot. I thought it would be cool to adapt these to power an Arduino from a phones MicroSD port. This would solve my problem of having to deal with USB OTG power and would be a nicer solution as the USB port could still be used.

My question; does the MicroSD port need signalling before VDD is powered?

And additionally, would it be possible to communicate a signal over the data lines with Arduino, or would that be really hard? A very minimalistic signal would already be nice.

Lastly, what can I expect to be the amperage to be supplied? Looking at a datasheet from a typical MicroSD card I see it requires 100ma to operate, so I figure at least that.

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    \$\begingroup\$ Much of this would depend on the particular phone but you could get an idea by reading up on card interfaces, generally and for the SoC and board in use. It is probably not a good idea, and you're likely to find signalling very difficult without a custom build of Android. Some Rockchip tablet SoCs had their console serial port multiplexed with some uSD slot signals, that was a fun use for those extender ribbons. \$\endgroup\$ – Chris Stratton Dec 23 '18 at 17:56
  • \$\begingroup\$ Thanks for the answer. I guess it will be too complex for me to take on. I thought it might be possible since there are some MicroSD host breakouts for Arduino, so the reverse might be possible too. Maybe some day there will be a clever engineer that'll build it, if possible. I'll take your advice and comb over a datasheet, see if it's at least possible to get power. I figure if I'd insert an actual MicroSD card I could tap into the VDD line at the very least. \$\endgroup\$ – LongLog Dec 23 '18 at 18:44
  • \$\begingroup\$ Apparently it has been done: hackaday.com/2015/06/28/hackaday-prize-entry-an-sd-card-arduino \$\endgroup\$ – LongLog Dec 23 '18 at 19:47
  • \$\begingroup\$ That is not compatible with something that expects an SD card; it might work if you can bit bang the SoC pins involved or operate them as SPI. \$\endgroup\$ – Chris Stratton Dec 23 '18 at 19:55
  • \$\begingroup\$ Yeah sorry, it seems that that hackaday entry never got communication working either, but it does rely on the power output so there's that. It says there that the minimum clock frequency is 25Mhz and that's a bottleneck (for the Arduino). I wonder if an ESP could handle it, but it might require too much current. \$\endgroup\$ – LongLog Dec 23 '18 at 20:26

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