DC 1 L 293 H Bridge

Initial report by Carlyn?, 23, March, 2006

This report is designed to allow you to create a reusable module for Always-On DC motor applications based on a L293D H-Bridge. This report is draws heavily from Tom Igoe’s Intro to Physical Computing resources.

Applications and Background

The DC Motor are simple motors to conrol and generally used for speed and power. There are two terminals, and when you apply direct current to one terminal and ground the other, the motor spins in one direction. When you apply current to the other terminal and ground the first terminal, the motor spins in the opposite direction. By switching the polarity of the terminals, you reverse the direction of the motor.The L293D is a standard Quadruple Half-H Driver and it is used in the case of DC motor control to mediate switching directions. A simple transistor like the TIP120 can be used if no direction switching is required. The L293D can easily be replaced with the SN754410.

More general disscussion of DC motors

http://tigoe.net/pcomp/motors.shtml
http://tigoe.net/pcomp/dc-motor-control.shtml
http://tigoe.net/pcomp/labs/lab-motors.shtml

Datasheets for L293D and SN754410

http://focus.ti.com/docs/prod/folders/print/l293d.html
http://focus.ti.com/docs/prod/folders/print/sn754410.html

Circuit Diagram

Breadboard Style

http://flickr.com/photos/pcomp/sets/72057594082854160/

Perfboard Style

Printed Board Style

Code

PicBasic Pro code:

' switch is on RC4:
switchPin	var portc.4
input switchPin

' H-bridge is on RC2 and RC3. Enable is on pin RC1
motor1Pin	var	portc.2
motor2pin	var	portc.3
speedPin 	var portc.1

output motor1Pin
output motor2pin
output speedPin

' start with speed on:
high speedPin

main:

	' switch direction:
	if (switchPin = 1) then
		low motor1Pin
		high motor2Pin
	else
		low motor2Pin
		high motor1Pin
	endif

	' blinking LED to tell that the program is still running:
	high portb.0
	pause 50
	low portb.0
	pause 50
goto main

Wiring Code (for Arduino board):

/*
  DC motor control
  by Ryan Holsopple

  modification of Tom Igoe's DC motor code   
  I added function to start motor turning in one direction
  I raised the threshold for my pot to work
  **r.holsopple

  Created 8 Feb. 2006

*/


int sensorValue = 0;     // the variable to hold the analog sensor value
int sensorPin = 0;       // the analog pin with the sensor on it
int motorPin = 9;        // the digital pin with the motor on it
int threshold = 300;     // the theshold of the analog sensor below which the motor should turn on
int forwardPin = 7;
int backwardPin = 8;

// prototype of the function that changes the motor's speed:
void changeMotorSpeed();

//function to begin motor turning in one direction
void forwardDirection();

void setup() {
 // declare the inputs and outputs:
 pinMode(motorPin, OUTPUT);
 pinMode(forwardPin, OUTPUT);
 pinMode(backwardPin, OUTPUT);
 pinMode(sensorPin, INPUT);
}

void loop() {
  //  read the analog sensor
  sensorValue = analogRead(sensorPin);
  //  determine whether its above or below the threshold
  if (sensorValue > threshold) {    // it's above the threshold
    // turn off the motor
    digitalWrite(motorPin, LOW);
  } 
  else {
    //start motor turning forward
    forwardDirection();
    // change the speed of the motor based on the sensor value:
    changeMotorSpeed();
  }
}

////////////////////////////////////////
void forwardDirection(){
  digitalWrite (forwardPin, HIGH);
  digitalWrite (backwardPin, LOW);
}
void changeMotorSpeed() {
  analogWrite(motorPin, sensorValue);
}

The simple version:

int motorPin = 9;  // where the transistor's base is attached
int analogPin = 0;  // Analog input number for the potentiometer

int analogValue = 0;  // variable for the analog reading

void setup()  {
pinMode(motorPin, OUTPUT);

}

void loop() {
  analogValue = analogRead(analogPin);

  if (analogValue > 512) {
  // turn the motor on
  digitalWrite(motorPin, HIGH);
  } else {
  // turn the motor off
  digitalWrite(motorPin, LOW);
  }

}