When reading and writing to the SD card, the key problem is timing. The program must adhere to strict read/write timing to read and write data to/from the SD card.
Code Description S Start bit (= 0) T Transmitter bit (Host = 1; Card = 0) P One-cycle pull-up (= 1) E End bit (= 1) Z High impedance state (-> = 1) Code Description D Data bits X Don’t care data bits (from SD card) * Repetition CRC Cyclic redundancy code bits (7 bits) Gray / White Card Active / Host Active
May use less power, parts may be less expensive, we would gain practical knowledge and experience
More time would be required, voltage regulators still needed so flyback regulator and transformer may be superfluous, not a very big part of project so may not be worth several weeks of effort that can be spent on other parts of the project