Line counting sensor?
I have a group (20) of small robots that need to all end on a certain line in a grid. My question is how can I get each car to count the number of lines it crosses and when it reaches the right number it stops. The problem is I have a budget of $75 dollars to make the guidance for every car. If there was maybe some sort of central controller that would work for each or maybe it is just cheep enough to make a simple set-up for each one. Any comments or questions would be much appreciated.
Thanks in advance,