Hi,
here is a super simple circuit for a line following robot.
Use two IR-reflective sensors along a track which should be gray or black. As long as both sensors "see" a reflective surface (focussing 3mm above object) the robot will move straight.
If the centerline is left (by moving across it) one sensor's view is interrupted giving control signal to an H-bridge, which drives and reverses the steering motor.
The small single sided PCB layout accomodates all parts (except for the enable switch) and measures 52.5463X36.83 (2.07X1.45")
The ground fill underneath the H-bridge IC is necessary for cooling.
Since there is no control signal to resume normal steering after course correction the robot will very likely zigzag along the course.
I just made up the circuit for you for a start.
Boncuk