Line Following Robot without Microcontroller

Level : Beginners

You Require:

1. Power Supply Circuit (Click here if you've not seen it yet)

2. IC LM324 Op-Amp

3. IC L293D Motor Driver

4. Resistors 2X10kΩ, 2X330Ω

5. 2X IR LED Tx Rx pairs
6. 2X 10k Potentiometer


Hardware


1. Chassis
2. 2X9V Geared DC Motors
3. Castor wheel
4. 2XWheels

A line follower is an autonomous robot which can follow a specific colored line painted on a surface of different contrast, such as white on black or black on white. Here I'll show you how to make a black on white line follower.

click on image to enlarge

Before going into the actual tutorial, let me explain you a small concept about light. You must be knowing that the light that strikes any platform is reflected. The reflection and absorption coefficient of light depend upon material, color of platform and other factors. In simple words the black surface absorbs the light and the white surface reflects it, this is the basic concept behind making a line follower.

So our robot's sensor has two parts which are emitter and receiver. The emitter continuously emits the infrared light and the receiver absorbs it after getting reflected from the black or white surface. The voltage across the receiver is directly proportional to the reflected light it absorbs. So for white surface, maximum reflection occurs so maximum voltage across the receiver and vice-versa.

click on image to enlarge

Firstly, lets make the sensor circuit for our robot. We would need two of these sensors to sense either sides of the line.Now the voltage across the receiver is a analog value but we would need a digital value to make the robot work. So we use a Op-Amp IC LM324 to convert this analog value into a digital value such that when sensor senses black line, it outputs logic low (0 volts) and when it senses white line it outputs logic high (+5 volts)

LM324 is used as a comparator here. We give a reference voltage to its input using a 10k pot. When the voltage across the receiver is less than this reference voltage, the comparator gives low output and when the voltage is more than the reference point, the comparator gives a high output.

click on image to enlarge

The table below shows how the robot senses its position on the line:-

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Motor Driver L293D


Well a LM324 IC cannot drive motors directly since it can't supply the power which can drive the motors. So we use a motor driver IC which takes a low voltage input and supplies high power to the motors

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The table below shows the various input combinations and the direction of motion related to that combination:-

There are two enable pins for this IC, one is for Motor 1 and other is for Motor 2. The Motor would be only enabled if this pin is provided with logic high, or else the motor would stop. We connect the sensor output to the two enable pins. I guess you  must have already got the idea as to how to connect the comparator's output to the motor driver's Enable pins. Still didn't get it? then look at the image below.

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The Input pins 2 and 15 are grounded and pins 7 and 10 are supplied with 5 volts so when the motors are enabled, they will only in forward direction.




Attach the motors and castor wheel to the chassis and fit in the wheels into the motor shaft. Connect the wires coming from motor to the output of the motor driver IC. Thats all! Your own made Autonomous Line Follower Robot is ready to run now!