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Author Topic: SD Card Adapter, signal lines on this schematic  (Read 643 times)
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See the attached schematic for an SD Card module that is widely available.

As far as level shifting goes, it can be done simply with two resistors forming a potential divider, but this one has a single 10k resistor on each signal line acting as a default pull-up to 3v3.

How is this working? As far as I can see, those lines have a nominal 3v3 on via the pull-up, so when the uC is connected and a signal occurs, teh SD card line would either pull down hard to 0v, with 3v3 across the resistor, or be pulled up to 5v, with 1.7v across the resistor (5v-3v3; in opposite polarity).

What am I missing here, as it doesn't seem to do anything expect provide a default pull-up of the lines.


* sd-card-module-reader_schematic.jpg (58.13 KB, 500x740 - viewed 132 times.)
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Yes, this module does not comply with the SD Association's spec.

It fails with many if not most SD cards on 5V Arduinos. 

People have modified it with true level shifters http://forum.arduino.cc/index.php?PHPSESSID=7b37nictl7rhle1esm0j5jmnn2&topic=170273.msg1268845#msg1268845
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