You don't actually need to measure the TOF of the light to do this. To measure tof to any reasonable precisiion would take sub-picoedcond resolution in your timers, so that leaves out the 8052 !

What you CAN do in some cases is modulate various frequencies into the intensity of the light source, then amplify the return signal and measure its phase at each of the various test frequencies.

I leave it as an exercise for the pupil to develop suitable collimating optics, amplifiers and phase measurement electronics.

The CPU is the absolutely easiest bit !

Steve