Planning to realize an SD Card interface for Arduino, since it requires 3.3V supply, I've realized a simple one based on a general purpouse LM317 Voltage Regulator.
This is the schematic I've used:
In LM317 theory, using 330R (R1) and 545 (R2) one should get 3.31V. Actually, 330R is common, and I've got 545R by adding 470R and 75R in series.
This is the circuit on a stripboard:
And this is an example of realization:
Giving 5V input, the measured output is 3.33V.