HOW TO: Make a line follower bot using L293D H-Bridge IC

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The line follower itself clear it's meaning that it is a Robot which traces or follows a specific path. The principle of the line follower is based on sensing the background surface 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 the motors. the output of the senors are not directly fed to the motors instead a L293D IC is used in between the sensors output and motors input. The sensor output is given to the input in of L293D and the output pin of IC is connected to the motors. the L293D IC is having two H-bridges which is capable to rotate motors in directional.

In our line follower we are using DC gear motors because it is easy to control, require only two signals, to change the direction of rotation just reverse the polarity and speed can be controlled by the voltage difference.

In this project we are using IR sensors. IR sensors consist an IR LED (emitter), Photodiode (detector) and an op-amp. the OP-amp IC which is used here is LM358, which is an 8-pin IC having two inbuilt op-amps.
Circuit diagram of IR sensor


we know that the white surface reflects all the radiations falls on it whereas the black absorbs them. When the supply is given to IR sensors, LED starts emitting light radiations. if the surface 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 photodiode which is connected in revrse 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.
Internal Block diagram of L293D





Remember, on white surface- comparator output is high and on black surface- comparator output is low.
Pin diagram of 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.


NOT gates are usually used as buffers in the H-bridge to strengthen the signal and also used as repeaters.


Working Model




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