Shift 0-1.8V logic to 0-5V logic
There is also a single-NPN possibility in that question that may work for your setup provided the output impedance of the 1.8V part is much smaller than the input impedance of the 5V part (this is certainly the case here). You'd have to adjust the resistor values.

Disclaimer : I'm the op of the linked question, but didn't use that setup extensively (I ultimately went for the 2-diode route).