HOW TO MAKE LINE FOLLOWING ROBOT

It is a machine that follows a line, either a black line on white surface or vise-versa. For Beginners it is usually their first robot to play with. In the following steps you will completely understand the concept of line follower.

Now we are going to build a line follower which will follow black line on a white surface, we will be using two IR sensor pair which will have an IR LED and Photo diode.

WORKING OF IR SENSOR:

Generally IR rays will be reflected by white surface while black surface will absorb IR rays.In the line follower that we are going to build, both the IR sensors will be on the white surface . IR rays will be emitted and reflected back which will be detected by the Photo diode, in this state the IR sensor will send a HIGH digital signal ("1"). similarly when the sensor is on a black surface IR rays will be emitted and will not be reflected back which will be absorbed by the black surface, in this state the IR sensor will send LOW digital signal ("0"). Thus with these digital values 1 and 0 we can easily identify the state of the sensors.

Component required 

1) IC7805 Voltage Regulator - 1
2) L293D Motor Driver - 1
3) IR LED pair - 2
4) 300-500rpm DC Motor - 2
5) Battery 9v-12v - 1
6) Breadboard - 1
7) Chasis - 1
8) Castor wheel - 1
9) Wheels - 2

Give the connections as per the circuit given and place the whole setup on the chasis.
L293D:
The digital signal given to the INPUT 1,2,3 and 4 of L293D will be thrown back to the OUTPUT 1,2,3 and 4 respectively. The INPUT 2 and 3 of L293D is connected to ground which is LOW("0") and the signal from the IR sensors are connected to INPUT 1 and 4. Hence the value of OUTPUT 2 and 3 will be constantly LOW("0") while the value of OUTPUT 1 and 4 will be HIGH("1") when the IR sensor is on the white surface and will be LOW("0") when the sensor is on black surface.
that's it, now you can enjoy your own simple Line follower robot
If u have any doubts feel free to ask