SIK Galileo - Part 8: Driving a Servo Motor a learn.sparkfun.com tutorial

Available online at: http://sfe.io/t282

Introduction

Servos are ideal for embedded electronics applications because they do one thing very well that motors cannot – they can move to a position accurately. By varying the pulse width of the output voltage to a servo, you can move a servo to a specific position. For example, a pulse of 1.5 milliseconds will move the servo 90 degrees. In this circuit, you’ll learn how to use PWM (pulse width modulation) to control and rotate a servo.

Parts Needed

You will need 1x servo and 8x jumper wires. If you are following through all of the SIK Galileo tutorials we suggest getting these parts:

Servo - Generic (Sub-Micro Size)

In stock ROB-09065

Here is a simple, low-cost, high quality servo for all your mechatronic needs. This servo is very similar in size and specifi…

8.95

Jumper Wires Standard 7" M/M Pack of 30

In stock PRT-11026

If you need to knock up a quick prototype there's nothing like having a pile of jumper wires to speed things up, and let's fa…

4.95

How to Use a Breadboard

May 14, 2013

Welcome to the wonderful world of breadboards. Here we will learn what a breadboard is and how to use one to build your very first circuit.

Pulse-width Modulation

February 27, 2013

An introduction to the concept of pulse width modulation.

Galileo Getting Started Guide

January 23, 2014

An introduction to the Arduino/Intel Galileo, and how to begin using the nifty x86, 400MHz Arduino.

If you are following along with the SIK Galileo tutorials, it is helpful to view the tutorials before this one:

Hardware Hookup

Ready to start hooking everything up? Check out the Fritzing diagram below, to see how everything is connected. Pay special attention to the component’s markings indicating how to place it on the breadboard. Polarized components can only be connected to a circuit in one direction.

Connect 3x jumper wires to the female 3 pin header on the servo. This will make it easier to breadboard the servo.

Fritzing Diagram

Having a hard time seeing the circuit? Click on the Fritzing diagram to see a bigger image. Please kept in mind your servo will have a white wire instead of yellow.

Code To Note

#include <Servo.h>

#include is a special “preprocessor” command that inserts a library (or any other file) into your sketch. You can type this command yourself, or choose an installed library from the “sketch / import library” menu.

Servo servo1;

servo1.attach(9);

The servo library adds new commands that let you control a servo. To prepare the Galileo to control a servo, you must first create a Servo “object” for each servo (here we’ve named it “servo1”), and then “attach” it to a digital pin (here we’re using pin 9).

servo1.write(180);

The servos in this kit don’t spin all the way around, but they can be commanded to move to a specific position. We use the servo library’s write() command to move a servo to a specified number of degrees(0 to 180). Remember that the servo requires time to move, so give it a short delay() if necessary.

Copy and paste the following code into the Arduino IDE. Hit upload and see what happens!

language:cpp
/*
SparkFun Inventor's Kit Galileo
Example sketch 08

SINGLE SERVO

  Sweep a servo back and forth through its full range of motion.

  A "servo", short for servomotor, is a motor that includes
  feedback circuitry that allows it to be commanded to move to
  specific positions. This one is very small, but larger servos
  are used extensively in robotics to control mechanical arms,
  hands, etc. You could use it to make a (tiny) robot arm,
  aircraft control surface, or anywhere something needs to be
  moved to specific positions.

Hardware connections:

  The servo has a cable attached to it with three wires.
  Because the cable ends in a socket, you can use jumper wires
  to connect between the Arduino and the servo. Just plug the
  jumper wires directly into the socket.

  Connect the RED wire (power) to 5 Volts (5V)
  Connect the WHITE wire (signal) to digital pin 9
  Connect the BLACK wire (ground) to ground (GND)

  Note that servos can use a lot of power, which can cause your
  Arduino to reset or behave erratically. If you're using large
  servos or many of them, it's best to provide them with their
  own separate 5V supply. See this Arduino Forum thread for info:
  http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1239464763

This sketch was written by SparkFun Electronics,
with lots of help from the Arduino community.
This code is completely free for any use.
Visit http://learn.sparkfun.com/products/2 for SIK information.
Visit http://www.arduino.cc to learn about the Arduino.

Version 2.0 6/2012 MDG
*/


// If we had to write a sketch to control a servo from scratch,
// it would be a lot of work. Fortunately, others have done the
// hard work for you. We're going to include a "library"
// that has the functions needed to drive servos.

// A library is an set of additional functions you can add to
// your sketch. Numerous libraries are available for many uses,
// see http://arduino.cc/en/Reference/Libraries for information
// on the standard libraries, and Google for others. When you're
// using a new part, chances are someone has written a library
// for it.

#include <Servo.h>  // servo library

// Once you "include" a library, you'll have access to those
// functions. You can find a list of the functions in the servo
// library at: http://arduino.cc/en/Reference/Servo
// Most libraries also have example sketches you can load from
// the "file/examples" menu.

// Now we'll create a servo "object", called myservo. You should
// create one of these for each servo you want to control.
// You can control a maximum of twelve servos on the Uno
// using this library. (Other servo libraries may let you
// control more). Note that this library disables PWM on
// pins 9 and 10!

Servo servo1;  // servo control object


void setup()
{
  // We'll now "attach" the servo1 object to digital pin 9.
  // If you want to control more than one servo, attach more
  // servo objects to the desired pins (must be digital).

  // Attach tells the Arduino to begin sending control signals
  // to the servo. Servos require a continuous stream of control
  // signals, even if you're not currently moving them.
  // While the servo is being controlled, it will hold its
  // current position with some force. If you ever want to
  // release the servo (allowing it to be turned by hand),
  // you can call servo1.detach().

  servo1.attach(9);
}


void loop()
{
  int position;

  // To control a servo, you give it the angle you'd like it
  // to turn to. Servos cannot turn a full 360 degrees, but you
  // can tell it to move anywhere between 0 and 180 degrees.

  // Change position at full speed:

  servo1.write(90);    // Tell servo to go to 90 degrees

  delay(1000);         // Pause to get it time to move

  servo1.write(180);   // Tell servo to go to 180 degrees

  delay(1000);         // Pause to get it time to move

  servo1.write(0);     // Tell servo to go to 0 degrees

  delay(1000);         // Pause to get it time to move

  // Change position at a slower speed:

  // To slow down the servo's motion, we'll use a for() loop
  // to give it a bunch of intermediate positions, with 20ms
  // delays between them. You can change the step size to make
  // the servo slow down or speed up. Note that the servo can't
  // move faster than its full speed, and you won't be able
  // to update it any faster than every 20ms.

  // Tell servo to go to 180 degrees, stepping by two degrees

  for(position = 0; position < 180; position += 2)
  {
    servo1.write(position);  // Move to next position
    delay(20);               // Short pause to allow it to move
  }

  // Tell servo to go to 0 degrees, stepping by one degree

  for(position = 180; position >= 0; position -= 1)
  {
    servo1.write(position);  // Move to next position
    delay(20);               // Short pause to allow it to move
  }
}

What You Should See

You should see your servo motor move to various locations at several speeds. If the motor doesn’t move, check your connections and make sure you have verified and uploaded the code, or see the troubleshooting section.

Real World Application:

Robotic arms you might see in an assembly line or sci-fi movie probably have servos in them.

Troubleshooting

Servo Not Twisting

Even with colored wires it is still shockingly easy to plug a servo in backward. This might be the case.

Still Not Working

A mistake we made a time or two was simply forgetting to connect the power (red and brown wires) to +5 volts and ground.

Fits and Starts

If the servo begins moving then twitches, and there’s a flashing light on your Galileo, the power supply you are using is not quite up to the challenge. Using a wall adapter instead of USB should solve this problem.

Resources and Going Further

Ready to continue? Have fun learning about the Galileo and follow along through all the SIK Galileo tutorials.

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