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Topic: 1 GB microSD on MAC (Read 2 times) previous topic - next topic

rebcarot

I did connect the VCC to 3.3V. I didn't do anything to 5V SPI SCK and MOSI signals, what would you recommend? The write/read test programs has worked once with the CS, DI, SCK and DO connected directly to the mega.

fat16lib

Don't try any other micros SD cards.  They may be damaged by the high voltage signals.
As Sparkfun says about their shield:
Quote
All new microSD shields have a voltage converter chip on-board that converts the Arduino 5V signals to 3.3V signals in accordance with SD specifications. No more 'blown up' SD cards!


The best approach is to use a level shifter like these adapters/shields

http://www.adafruit.com/products/254

http://www.gravitech.us/micaad.html

http://www.sparkfun.com/products/9802

You could try resistor level shifters but these don't work well with many cards.  If you try this, slow down the SPI clock.

rebcarot


fat16lib

It might work but this is a poor solution.  Resistor based level shifters fail with many newer SD cards since new cards have edge detectors for the signals and resistors round signal edges.

This is the reason that almost all commercial products now use semiconductor buffers/level shifters.

Good luck if you try it.  You might want to download the new SdFat beta and enable CRC to detect any data errors and slow down the SPI clock.

The SdFat beta with CRC is SdFatBeta20120327.zip http://code.google.com/p/beta-lib/downloads/list

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