You can change 5V into 3.3V using two resistors...
Sometimes it can work with just 1 resistor. Many devices now have input clamping diodes. With a resistor, a 5v->3.3v drive will be limited to 3.3v+Vfwd on the clamping diode, and will for sure to be recognized as high.
The issue is more with 3.3v -> 5v drive: a 3.3v logic high may not be recognized by the 5v device as logic high. The solution? Use a pull-up resistor.
So here is the set-up: use a current limiting resistor between your 5v and 3.3v device. On the 5v device side of the resistor, use a pull-up resistor. Resistor values not particular, anything this side of 10k should work.
That's a poorman's level converter.