user7728: I have some audio files in an SD card and I want to play them using Arduino, thus connect the SD card to the Arduino. Since the transfer of the data will be from the SD card (+3.3V) to the Arduino (+5.0V) and not vice versa, is a level shifter necessary? 

user37622: You can't use SD card without level conversion from 5 V to 3.3 V. Clock and CS line are driven by the master, and the master must request over MOSI the data to read.

user53178: i have a cheap generic chinese off-brand sd Card module and it does not even work if i do connect vcc to 3v3 so i use it with 5v. and i do not bother to add a Level shifter on the bus lines. and writing text to a file on the sd Card does work like a charm this way. so i would say no you not neccesarily Need the Level shifter but feel free to add it anyway and see if it works this way too. 

7728: <p>I have some audio files in an SD card and I want to play them using Arduino, thus connect the SD card to the Arduino. Since the transfer of the data will be from the SD card (+3.3V) to the Arduino (+5.0V) and not vice versa, is a level shifter necessary? </p>
 37622: <p>You can't use SD card without level conversion from 5 V to 3.3 V. Clock and CS line are driven by the master, and the master must request over MOSI the data to read.</p>
 53178: <p>i have a cheap generic chinese off-brand sd Card module and it does not even work if i do connect vcc to 3v3 so i use it with 5v. and i do not bother to add a Level shifter on the bus lines. and writing text to a file on the sd Card does work like a charm this way. so i would say no you not neccesarily Need the Level shifter but feel free to add it anyway and see if it works this way too. </p>
