DC motor direction control using L293d   
This is another tutorial for microcontroller interfacing series. This is all about how to interface/control a simple DC motor using microcontrollers. Controlling a DC motor is nothing but controlling the direction and speed of a motor. It is very necessary to go through motor controlling concept, if you are designing an autonomous robot.

How DC Motor works ???
Lets start with how actually DC motor runs. Direction control of a DC motor is very simple, just reverse the polarity, means every DC motor has two terminals out. When we apply DC voltage with proper current to a motor, it rotates in a particular direction but when we reverse the connection of voltage between two terminals, motor rotates in another direction.

Controlling using Micro Controllers !!!

I think you are now familiar how to change the direction of DC motor. Now let us consider how to control motor using Microcontroller provided:
1. Microcontroller provides us only digital logic (1 or a 0).
2. We cant provide polarity from microcontroller.
3. We cant connect motors to Controller as mostly motors runs on    volatage higher that +5V, and motors demands high current   (depends).
Now the solution to above limitations is use of a “H Bridge”.

It is a circuit which allows motor rotation in both directions. From four terminals of H bridge you can control a DC motor.
Using L293d Dual half H Bridge …
We can make our own H bridge using transistors but it will be better if we use a ready made IC named as L293d, its a dual half H brige IC.

we can drive a maximum of two DC motor and One stepper motor using one L293d.

Decision Table will look like

IN1    IN2    Motor1   
0    1    Rotates in one direction   
1     0    Rotates in other direction   

Similar is true for another motor connected to Out3 and Out4 of L293d and can be controled through IN3 and IN4. This is all about controlling direction of DC motor using L293d and ATmega16.

To control the speed of DC motor one can use a Pulse Width Modulated signal on Enable1 and Enable2 pins of L293d, this will result in controlled power input on motor, so speed is controlled.

Example program for DC motor control using L293d H bridge IC

This program Controls the direction of DC Motor connected to PORTC via L293D as shown in schematic.

It takes user input at two push buttons connected to PORTD_0 & PORTD_1 respectively.

When user presses button at PORTD_0 Motor rotates in one direction, Similarly it rotates in other 
direction when user press button at PORTD_1 


int main(void)
	DDRD=0x00;     // PORTD declared as input port
	PORTD=0xFF;    // PORTD Pull Ups enabled
	DDRC=0XFF;     // PORTC declared as output port
	PORTC=0x00;    // PORTC initialized



		if(!(PIND&0x01))            	// PIN D0 is used as input
			_delay_ms(50);      	// Debounce time<
			PORTC=0b00000010;   	// motor rotates in one particular direction
		else if(!(PIND&0x02))       	// PIN D1 is used as another input
			_delay_ms(50);      	// debounce time
			PORTC=0b00000001;   	// motor rotates in another direction
			PORTC=0x00;           	// Stop motor
		}  				// else end here

	} 					// While(1) ends here

}  						// main() ends here

Note- Do not connect toy cars small DC motor directly to L293d as they consume lot of current and has small internel resistance.


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