# Adafruit's Raspberry Pi Lesson 9. Controlling a DC Motor

## Overview

This lesson describes how to control both the speed and direction of a DC motor using Python and a L293D chip.  

![](https://cdn-learn.adafruit.com/assets/assets/000/003/643/medium800/learn_raspberry_pi_overview.jpg?1396799328)

In Lesson 8, we used the Pi to generate pulses to control the position of a servo motor. In this lesson we use pulses to control the speed of a regular DC motor and the L293D motor control chip to reverse the direction of the current through the motor and hence the direction in which it turns.

# Adafruit's Raspberry Pi Lesson 9. Controlling a DC Motor

## Parts

To build this project, you will need the following parts.

# Adafruit's Raspberry Pi Lesson 9. Controlling a DC Motor

## PWM

Pulse Width Modulation (or PWM) is a technique for controlling power. We use it here to control the amount of power going to the motor and hence how fast it spins.

The diagram below shows the signal from the PWM pin of the Raspberry Pi.  

![](https://cdn-learn.adafruit.com/assets/assets/000/003/652/medium800/learn_raspberry_pi_how_pwm_works.jpg?1396799428)

Every 1/500 of a second, the PWM output will produce a pulse. The length of this pulse controls the amount of energy that the motor gets. No pulse at all and the motor will not turn, a short pulse and it will turn slowly. If the pulse is active for half the time, then the motor will receive half the power it would if the pulse stayed high until the next pulse came along.

# Adafruit's Raspberry Pi Lesson 9. Controlling a DC Motor

## The PWM Kernel Module

Adafruit and Sean Cross have created a kernal module that is included with the [Occidentalis](http://learn.adafruit.com/adafruit-raspberry-pi-educational-linux-distro/occidentalis-v0-dot-2 "Link: http://learn.adafruit.com/adafruit-raspberry-pi-educational-linux-distro/occidentalis-v0-dot-2") distribution. For details of creating an Occidentalis [follow this link](http://learn.adafruit.com/adafruit-raspberry-pi-lesson-1-preparing-and-sd-card-for-your-raspberry-pi). If you want to use the module with Raspbian or some other distribution, then there is help on installing the kernel module into your environment [here](http://learn.adafruit.com/adafruit-raspberry-pi-educational-linux-distro/occidentalis-v0-dot-2).

You used the PWM and Servo Kernel Module in Lesson 8, to control a Servo. This time, you will use the same module to control the speed of the motor.

The modules interface uses a file type of interface, where you control what the output pin and therefore the servo is doing, by reading and writing to special files. This makes it really easy to interface with in Python or other languages.

The files involved in using the module to drive a servo are listed below. All the files can be found in the directory /sys/class/rpi-pwm/pwm0/

# Adafruit's Raspberry Pi Lesson 9. Controlling a DC Motor

## L293D

This is a very useful chip. It can actually control two motors independently. We are just using half the chip in this lesson, most of the pins on the right hand side of the chip are for controlling a second motor, but with the Raspberry Pi, we only have one PWM output.

![](https://cdn-learn.adafruit.com/assets/assets/000/003/653/medium800/learn_raspberry_pi_L293D.jpg?1396799434)

The L293D has two +V pins (8 and 16). The pin '+Vmotor (8) provides the power for the motors, and +V (16) for the chip's logic. We have connected pin 16 to the 5V pin of the Pi and pin 8 to a battery pack.  

# Adafruit's Raspberry Pi Lesson 9. Controlling a DC Motor

## Hardware

There are two reasons why we need to use a L293D chip in this project. The first is that the output of the Raspberry Pi is nowhere near strong enough to drive a motor directly and to try this may damage your Raspberry Pi.

Secondly, in this lesson, we want to control the direction of the motor as well as its speed. This is only possible by reversing the direction of the current through the motor, something that the L293D is designed to do, with the help of two control pins.

![](https://cdn-learn.adafruit.com/assets/assets/000/003/654/medium800/learn_raspberry_pi_breadboard.png?1396799472)

The project fits nicely on a half-sized breadboard.

# Adafruit's Raspberry Pi Lesson 9. Controlling a DC Motor

## Software

Since we need to control pins (connected to pin 4 and 17 of the GPIO) we also need to use the GPIO library. For details of this, see [Lesson 4](http://learn.adafruit.com/adafruits-raspberry-pi-lesson-4-gpio-setup "Link: http://learn.adafruit.com/adafruits-raspberry-pi-lesson-4-gpio-setup").

There are lots of ways to get the sketch from the listing below onto your Raspberry Pi. Perhaps the easiest is to connect to your Pi using SSH (See [Lesson 6](http://learn.adafruit.com/adafruits-raspberry-pi-lesson-6-using-ssh)) opening an editor using the command below:

```
nano motor.py
```

and then pasting in the code below, before saving the files using CTRL-x.

![](https://cdn-learn.adafruit.com/assets/assets/000/003/655/medium800/learn_raspberry_pi_ssh_edit.png?1396799500)

Here is the code:

```
import RPi.GPIO as io
io.setmode(io.BCM)

in1_pin = 4
in2_pin = 17

io.setup(in1_pin, io.OUT)
io.setup(in2_pin, io.OUT)

def set(property, value):
    try:
        f = open("/sys/class/rpi-pwm/pwm0/" + property, 'w')
        f.write(value)
        f.close()	
    except:
        print("Error writing to: " + property + " value: " + value)
 
set("delayed", "0")
set("mode", "pwm")
set("frequency", "500")
set("active", "1")

def clockwise():
    io.output(in1_pin, True)    
    io.output(in2_pin, False)

def counter_clockwise():
    io.output(in1_pin, False)
    io.output(in2_pin, True)

clockwise()

while True:
    cmd = raw_input("Command, f/r 0..9, E.g. f5 :")
    direction = cmd[0]
    if direction == "f":
        clockwise()
    else: 
        counter_clockwise()
    speed = int(cmd[1]) * 11
    set("duty", str(speed))
```

The Python program first sets-up the two GPIO pins to be outputs. It then defines the same convenience function (“set”) that we used in Lesson 8, to write to the PWM Kernel Module. This is then used to set the parameters for PWM.

There are two other functions defined, “clockwise” and “counter\_clockwise”, that control the direction of the motor by changing the two input pins.

If both control pins are HIGH, or both LOW then the motor will be stopped. But if IN1 is HIGH and IN2 LOW it rotates in one direction, reversing in direction if the values of IN1 and IN2 are reversed.

The main loop of the program waits for you to enter commands in the format of a letter (“f” or “r”) and a digit between 0 and 9. The letter sets the direction of the motor and the digit the speed, by multiplying the digit by 11 to give a value between 0 and 99 that the PWM library expects.

# Adafruit's Raspberry Pi Lesson 9. Controlling a DC Motor

## Test & Configure

To run the program, you will need to run it as super user to get access to the GPIO pins, so type:

```
sudo python motor.py
```

You will then get a prompt for you to enter a command. Try entering a few 2 letter commands as shown below.

```
$sudo python motor.py
Command, f/r 0..9, E.g. f5 :f9
Command, f/r 0..9, E.g. f5 :r4
Command, f/r 0..9, E.g. f5 :
```


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