Having read this excellent answer on FPGA's vs Microcontrollers I have a few queries.
I recently completed a project that utilised reflectance sensors. Simply put, it reads the reflectance by measuring the discharge time across a capacitor. However, if I wanted to utilise an FPGA for this project, how would one go about interfacing such a sensor with an FPGA? I've written VHDL before with ModelSim, and synthesised using Xilinx, so I have a basic grasp of how VHDL works.
In general, are FPGAs and microcontrollers interchangeable? What is the best way to interface external sensors, such as the ones above which are digital, with an FPGA?