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Topic: Pro Mini 5V and cheap SD module from Ebay (Read 91 times) previous topic - next topic

Dwacito

Hi all,

has anyone experience using cheap microSD breakouts from Ebay such as this one: click here with a 5V pro mini?

I'm having trouble getting them to work. They do work fine when the FTDI module is plugged into the Pro Mini (with or without the USB cable connected to the FTDI). As soon as I remove the FTDI the Pro Mini isn't able to communicate with the SD module (the file is not even created on the card).

Appreciate any help, even someone saying "yes I got these modules to work with a 5V pro mini". Many thanks!

Dwacito

Updating this as I seem to have found the problem.

I was using an NPN (2n2222) to switch power to the card (low side).
I had a 1kOhm resistor between Arduino pin and base.

It seems like changing the base resistor to 30kOhm (!) solved my problem.

I also tried switching high side instead (with NPN+pnp) and it works fine too.

I don't fully understand the resistor change to be honest. Current through base is 0.4mA so according to the datasheet with a current gain of 100 that would allow only 40mA to flow through collector. But I've read SD cards can take up to 150mA during writes so I'm not sure how it's still functioning. I measured about 35mA through collector when using the card so maybe it's actually not using that much current.

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