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?
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.