Lab: DC Motor Control Using an H-Bridge

Last edited 31 August 2014 by Tom Igoe

Introduction

In this tutorial, you’ll learn how to control a DC motor’s direction using an H-bridge.

To reverse a DC motor, you need to be able to reverse the direction of the current in the motor. The easiest way to do this is using an H-bridge circuit. There are many different models and brands of H-Bridge. This tutorial uses one of the most basic, a Texas Instruments L293NE or a Texas Instruments SN754410.

If you simply want to turn a motor on and off, and don’t need to reverse it, for example if you’re controlling a fan, try the tutorial on controlling high current loads with transistors.

What You’ll Need to Know

To get the most out of this lab, you should be familiar with the following concepts. You can check how to do so in the links below:

Things You’ll Need

For this lab you'll need:
Solderless breadboard Hook-up wire Arduino LEDs 10K Resistors
Solderless Breadboard 22-AWG hookup wire Arduino microcontroller Light emitting diodes – LED 10Kohm resistors
Switch L293NE H-bridge DC power supply DC motor
Switch L293NE or SN754410 H-bridge 12V DC power supply DC motor

Prepare the breadboard

Connect power and ground on the breadboard to power and ground from the microcontroller. On the Arduino module, use the 5V and any of the ground connections:

LabBBTemplate

Made with Fritzing

Add a Digital Input (a switch)

Connect a switch to digital input 2 on the Arduino.

LabDCMotorH-BridgeSwitch_schem LabDCMotorH-BridgeSwitch_bb

Find a motor

Find yourself a DC motor that runs on low DC voltage within the range of 5 – 15V. RadioShack often sells several small DC motors, the NYU Book Store on occasion has a few, the junk shelf is almost always a goldmine for discarded motors and fans. Asking classmates and second years is another good approach.

Solder leads to the motor’s terminals. With DC motors, there is no polarity regarding the motor terminals so you can connect it any way you’d like.

Optional: Consider testing your motor with a bench power supply from the equipment room. Ask a teacher or resident if you need help setting one up. Begin by adjusting the voltage on the bench power supply and observe its effects. Take note of its speed at different voltages without dipping to low or too high.

Safety Warning: Running a motor at a voltage much lower or much higher than what it’s rated for could potentially damage or permanently destroy your motor. When the motor doesn’t spin, the voltage is too low. When the motor runs hot, or sounds like it’s straining, the voltage is too high.

Set up the H-bridge

L293NE H-bridge

This example uses an H-bridge integrated circuit, the Texas Instruments L293NE or Texas Instruments SN754410. There is one in your Physical Computing Kit, and the NYU Book Store and many distributors such as Digikey, SparkFun, Mouser and Jameco sell them as well.

Connect the motor to the H-bridge

Connect the motor to the H-bridge as follows:

LabDCMotorH-Bridge9V_schem LabDCMotorH-Bridge9V_bb

Or, if you are using an external power supply for the Arduino, you can use the Vin pin.

LabDCMotorH-Bridge9VVin_schem

If you need an external power supply, you can use any DC power supply or battery from 9 – 15V as long as your motor can run at that voltage, and as long as the supply can supply as much current as your motor needs.

Plug an external DC power source into the Arduino’s external power input. You may still leave your USB cable plugged in for quick and easy reprogramming. Whichever motor you use, make sure the power source is compatible (i.e. don’t use a 9V battery for a 3V motor!). The external voltage input is available at the Vin pin, so you can use it both to power the Arduino, and to power the motor.

Program the microcontroller

Program the microcontroller to run the motor through the H-bridge. First set up constants for the switch pin, the two H-bridge pins, and the enable pin of the H-bridge. Use one of the analogWrite pins (3,5,6,9,10, or 11) for the enable pin.

const int switchPin = 2;    // switch input
const int motor1Pin = 3;    // H-bridge leg 1 (pin 2, 1A)
const int motor2Pin = 4;    // H-bridge leg 2 (pin 7, 2A)
const int enablePin = 9;    // H-bridge enable pin

In the setup(), set all the pins for the H-bridge as outputs, and the pin for the switch as an input. The set the enable pin high so the H-bridge can turn the motor on.

void setup() {
    // set the switch as an input:
    pinMode(switchPin, INPUT); 

    // set all the other pins you're using as outputs:
    pinMode(motor1Pin, OUTPUT);
    pinMode(motor2Pin, OUTPUT);
    pinMode(enablePin, OUTPUT);
    pinMode(ledPin, OUTPUT);

    // set enablePin high so that motor can turn on:
    digitalWrite(enablePin, HIGH);
  }

In the main loop() read the switch. If it’s high, turn the motor one way by taking one H-bridge pin high and the other low. If the switch is low, reverse the direction by reversing the states of the two H-bridge pins.

void loop() {
    // if the switch is high, motor will turn on one direction:
    if (digitalRead(switchPin) == HIGH) {
      digitalWrite(motor1Pin, LOW);   // set leg 1 of the H-bridge low
      digitalWrite(motor2Pin, HIGH);  // set leg 2 of the H-bridge high
    }
    // if the switch is low, motor will turn in the other direction:
    else {
      digitalWrite(motor1Pin, HIGH);  // set leg 1 of the H-bridge high
      digitalWrite(motor2Pin, LOW);   // set leg 2 of the H-bridge low
    }
  }

Once you’ve seen this code working, try modifying the speed of the motor using the analogWrite() function, as explained in the Analog Lab. Use analogWrite() on the enable pin of the motor, and see what happens as you change the value of the analogWrite().

Get creative

This is a suggestion for a possible project. It’s not a requirement for the class homework.

Use your motor to make something move, vibrate, rise, fall, roll, creep, or whatever you can think of, in response to user input from a digital input device (switch, floor sensor, tripwire, etc). Look inside moving toys, you’ll find a number of excellent motors and gears you can re-purpose. See the innards of a cymbal monkey below as an example. Perhaps you can re-design the user interface to a toy, using the microcontroller to mediate between new sensors on the toy and the motors of the toy. Whatever you build, make sure it reacts in some way to human action.