i am thinking of implementing this in the following way.i will have a timer which starts on receiving the pulse from the first retro reflective target and when no signal is obtained ie at the black strips i trigger a counter which counts for the particular width and then for the 2nd target i will be using a different width.
also i have a doubt on microcontrollers.will i be able to run 2 programs simultaneously.i have to keep the stepper motor program running continuosly but when the target is received i will have to run the target recognition program.