I want to get a Leonardo communicating with an Arduino Pro Mini 3.3v ATmega 328. The two devices are only a couple inches apart. I am leaning toward using I2C to do this. What's the best way to deal with the different voltage levels between the two boards?
If you use 4k7 pull-up resistors to 3.3V, it should work with I2C.
There is some information here: Arduino Playground - I2CBi-directionalLevelShifter
I2C is not very fast, but since both SDA and SCL are used with open-collector, the 5V versus 3.3V is less of a problem than with other solutions.
Thanks I'll try that.