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[Reply #15 on:]

The problem is that the switching has to be automated in my case.
The PC generates files and sends the arduino a message via serial that it has finished.
Arduino then switches the SD card for the PC to write the files to it and switches back after it has finished.
The files are then available for the Arduino to read.

[Reply #16 on:]

Ok, so what you need is to have a USB to SD card adapter coming from the PC, and the 5v/3.3V SD card adapter coming from the arduino, with the control signals switched.
I would get a USB to SD card adapter like this
http://www.amazon.com/Datafab-KESD-USBA-Reader-Extension-Cable/dp/B002ZVE4HC

open the case, and wire from that connector to a buffer chip that does 3.3V signals, and wire the OE/ signal so its under Arduino control.

Then wire the Arduino SPI lines thru a 5V to 3.3V level converter like this, and wire the OE/ signal so its under Arduino control.
I have used 74AC125D, not the HC that is shown here, this is just what I happened to find first.

[Reply #17 on:]

Thank you CrossRoads for the help. It took me a few minutes to get your idea and to understand the schematic but now I got how it works.
I'll look for a buffer chip and have a try.

[Reply #18 on:]

  Great idea CrossRoads! I had thought of using a USB to SD card adapter but, I had no idea how it could be used. I already have an USB adapter at home so, I will definitely take a look at it and see if can use your idea.

Way to go!

[Reply #19 on:]

Hi CrossRoads...

before anything, thanks for the nice idea!! exactly what I'm looking for too!!

I tried to do your circuit with a SN74HC244 to simplify it even more, trying to get everything into just one chip, but for some reason I can't get it to work.

As my electronics background is not that great I can't figure this one out... so maybe you could shine some light on it for me?

SN74HC244 datasheet: http://www.ti.com/lit/ds/symlink/sn74hc244.pdf

It's weird because the SN74HC244 is exactly what the circuit needs... 2 sets of 4 bit gates!

any help would be greatly appreciated... I really wan't to understand and learn!!

cheers...
-H

[Reply #20 on:]

How are you powering the HC244? from 3.3V?
What did you do for the 9th gate?