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Line Following Robot Using L293D
Introduction:
The name line follower itself clear its meaning that it is a robot which traces or follows a specific
path .The principleof the line follower is based on sensing the background surface by making use of
IR sensor. Basically IR sensor takes input by detecting the reflection of the IR rays from the surface
and accordingly gives its output to the motors. The output of the sensors are not directly fed to the
motors instead a L293D IC is used in between the sensors output and motors input. The sensors
output is given to the input pin of L293D and the output pin of L293 IC is connected to the motors.
The L293D IC is having two H-bridges which is capable to rotate motor in bidirectional.
DC Gear Motors:
In our line follower dc gear motors are used.
WHY DC MOTOR?
Easy to control
Require only two signals
For change the direction of rotation just reverse the polarity
Speed can be controlled by the voltage
USE OF GEARS
To provide enough torque.
Increases the torque on the expense of speed.
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IR Sensors:
Sensors are basically electronic devices which are used to sense the changes that occur in their
surroundings. The change may be in color, temperature, moisture, sound, heat etc. They sense thechange and work accordingly. In IR sensor the there is emitter and detector. Emitter emits the IR rays
and detector detects it.
The IR sensor basically consists ofthree components:
IR LED (emitter)
Photodiode (detector)
Op-Amp
IR LED:
Fig. 1
IR LED is a light emitting diode which emits the IR radiations. The basic function of the emitter is to
convert electricity into light. It works on the principle of recombination of the electron-hole pair. As
in the conduction band of a diode, electrons are the majority carrier and in the valence band, holes
are majority carrier. So when an electron from a conduction band recombines with a hole of valance
band, some amount of energy is released and this energy is in the form of light. The amount of
energy released is depends upon the forbidden energy gap. The IR Led has two legs, the leg which is
longer is positive and other leg is negative.
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Photo Diode:
Photodiode PIN Photodiode
Fig. 2
The photodiode is a p-n junction diode which is connected in reverse bias direction. The basic
function of the detector is to convert light into electricity. As its name implies that it works
effectively only when the certain number of photon or certain amount of light falls on it. When there
is no fall of light on the photodiode it has an infinite resistance and act as an open switch but as the
light starts falling on the photodiode, the resistance becomes low and when the full intensity of light
fall on the photodiode then its resistance becomes zero and it starts act like a closed switch.
Basicallytwo typeof photodiodes:
PIN type P stand for p-type semiconductor.
I stand for intrinsic semiconductor.
N stand for n-type semiconductor.
Avalanche type
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Op-Amp:
Op-Amp stands for operational amplifier. It is a DC-coupled high gain amplifier with differential
inputs and single output. Typically the output of the op-amp is controlled by either negativefeedback or positive feedback. Due to the fact that it performs several operations like addition,
subtraction, multiplication, integration etc, it is named as operational amplifier. It has two inputs,
inverted (Pin 2) and non-inverted input (Pin3). The signal which is applied to the inverted input gives
output 180 degree out of phase with input whereas in the non-inverted input gives output in phase
with that of input. Op-amp has a variety of uses in different electronics devices. In the line follower
it is used in the comparator mode. The op-amp IC which is used here is LM358 IC, which is an 8-pin IC
having two inbuilt op-amps. In the comparator mode, the reference voltage is set at the inverted
input pin and then it is compared with the input at non inverted pin. As the voltages at two input
pins of op-amp is compared, as the voltage at Pin 3 exceeds the reference voltage at Pin 2 the output
of the comparator becomes high (5 V) otherwise it becomes low (0 V). The reference voltage at Pin 2is set with the help of variable resistor.
Types of Op-amp:
1. General purpose op-amp.
2. Special purpose op-amp.
Fig 3. Internal block diagram of LM358 IC
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Working:
Fig 4. Circuit diagram of IR sensor
We know that the white surface reflects all the radiations falls on it whereas the black color absorbs
them. When the supply is given to IR sensor, LED starts emitting light radiations. If the surface is of
white color then it reflects all the radiations. As these radiations starts falling on the photodiodewhich is connected in reverse bias, the resistance of the photodiode starts decreasing rapidly and the
voltage drop across the diode also decreases. The voltage at Pin 3 starts increases, as it reaches just
beyond the voltage of Pin 2 the comparator gives high output. In case of the black surface, LED emits
light but it is not reflected by the surface, so the photodiode detects nothing and its resistance
remains infinite. Hence the comparator gives low output.
White surface Comparator output is high.
Black surface Comparator output is low.
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Sensitivity of IR sensor:
The sensitivity of sensor means that how much effectively the sensor senses the change that is
occurring in its surrounding. The sensitivity of the IR sensor is controlled by reference voltage at pin 2using variable resistor.
Large value of reference voltage less sensitive.
Small value of reference voltage more sensitive.
MOTOR DRIVER IC (L293D)
L293D IC is a dual H-bridge motor driver IC. One H-bridge is capable to drive a dc motor in
bidirectional. L293D IC is a current enhancing IC as the output from the sensor is not able to drive
motors itself so L293D is used for this purpose. L293D is a 16 pin IC having two enables pins which
should always be remain high to enable both the H-bridges. L293B is another IC of L293 series having
two main differences with L293D.
Difference between L293D and L293B:
1. L293D can run a motor up to 600 mA whereas L293B can run up to 1 A.
2. L293D has protection diode whereas L293B doesnt have any such protection diode. Need to
add the protection diode manually.
NOT gates are usually used as buffers in the H-bridge to strengthen the signal and also used as
repeaters.
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Fig 5. Pin diagram of L293D IC
Block diagram of Working Model:
Fig 6. Connetion Diagram of Working Model
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IR Sensors
Photo DiodeIR LED
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Front View of Working Model
Thank You
By: Meetinder Singh BajwaExecutive, Robosapiens India
Mail to: meetbajwa@robosapiensindia.com
Website: http://www.robosapiensindia.com
http://www.robosapiensindia.com/mailto:meetbajwa@robosapiensindia.comRecommended