Sometimes, voltages collide. When you have parts that expect/speak at different voltage levels, you have to build a mediator to smooth things out. This SparkFun BOB-10403 uses PCA9306 two-channel bidirectional voltage-level translator on a nice, small breakout board.
The PCA9306 is a dual bidirectional I2C-bus and SMBus voltage-level translator that's operational on the low side from 1.0 V to 3.6 V and on the high side from 1.8 V to 5.5 V.
Simply apply your low- and high-side reference voltages to the VREF1 and VREF2 respectively, connect your I/O and drive the Enable pin high to open bidirectional voltage translation without the use of a direction pin!