Servo Motor Control with an Arduino

In this lab, you'll control a servomotor's position using the value returned from an analog sensor. Servos are the easiest way to start making motion with a microcontroller. Even though they don't turn 360 degrees, you can use them to create all sorts of periodic or reciprocating motions. Check out some of the mechanisms at Rob Ive's site for ideas on how to make levers, cams, and other simple machines for making motion.

Not all servos have the same wiring colors. For example, the Hextronik servos that come with Adafruit's ARDX kit use red for +5V,brown for ground, and mustrard yellow for control.

  int servoAngle = map(analogValue, 0, 1023, 0, 179);

  int servoAngle = map(analogValue, 0, 1023, 0, 179);

%lframe alt='Voila, your headers fit better!' hspace=10 width=200% | Voila, your headers fit better!

When you attach the servo, you'll need a row of three male headers to attach it to a breadboard. You may find that the pins don't stay in the servo's connector holes. Put the pins in the servo's connector, then push them down on a table gently. They will slide up inside their plastic sheaths, and fit better in your servo's sonnector.

header pins don't always
stay in a servo connector

Put them in and push gently
on a firm surface

%lframe alt='Voila, your headers fit better!' hspace=10 width=200% | Put them in and push gently
on a firm surface

Get Creative

Servo motors give you the power to do all kinds of things.

They can be used to push a remote contro button, in a pinch:

http://tigoe.net/ESBflash/img/remote.jpg (Project: Tom Igoe)

You can play drums (Project: Nick Yulman)

You can make a rat's tail move (project: Gabriela Gutiérrez)

If you've got 800 or so of them and a lot of time, you can build a wooden mirror (project: Daniel Rozin).

Come up with a project of your own that needs a little movement, and see if you can solve the problem with a servomotor.

First, find out the range of your sensor by using analogRead() to read the sensor and printing out the results.

(:toggle question1 init=hide show='What does that look like?' hide='Let me figure it out':)

  Serial.begin(9600);		// initialize serial communications

  int analogValue = analogRead(A0); // read the analog input 
  Serial.println(analogValue);		// print it

Now, map the result of the analog reading to a range from 0 to 179, which is the range of the sensor in degrees. Store the mapped value in a local variable called servoAngle.

(:toggle question2 init=hide show='I give up, how do I do that?' hide='Let me figure it out':)

  Serial.begin(9600);		// initialize serial communications

  int analogValue = analogRead(A0); // read the analog input 
  Serial.println(analogValue);		// print it

  // if your sensor's range is less than 0 to 1023, you'll need to
  // modify the map() function to use the values you discovered:
  int servoAngle = map(analogValue, 0, 1023, 0, 255);

} (:sourceend:)

Finally, add the servo library at the beginning of your code, then make a variable to hold an instance of the library, and a variable for the servo's output pin. In the setup(), initialize your servo using servo.attach(). Then in your main loop, use servoAngle to set the servo's position.

(:toggle question3 init=hide show='I give up, how do I do that?' hide='Let me figure it out':)

  Serial.begin(9600);		// initialize serial communications
  servoMotor.attach(servoPin);  // attaches the servo on pin 2 to the servo object

  int analogValue = analogRead(A0); // read the analog input 
  Serial.println(analogValue);		// print it

  // if your sensor's range is less than 0 to 1023, you'll need to
  // modify the map() function to use the values you discovered:
  int servoAngle = map(analogValue, 0, 1023, 0, 255);

  // move the servo using the angle from the sensor:
  servoMotor.write(servoAngle);                  

Pick any analog input and connect it to Analog pin 0 as you did in the Analog Input and Output Lab. Then connect an RC servomotor to digital pin 2. The yellow wire of the servo goes to the pin, and the red and black wires go to +5V and ground, respectively.

Not all servos have the same wiring colors. For example, the Hextronik servos that come with Adafruit's ARDX kit use red for +5V,brown for ground, and mustrard yellow for control.

Attach:Attach:servo_control_fsr_bb.png Δ Δ (Diagram made with Fritzing

 int servoPin = 2;       // Control pin for servo motor. As of Arduino 0017, can be any pin

(:cell:)

(Diagram made with Fritzing - download)

(Diagram made with Fritzing - download)

http://itp.nyu.edu/physcomp/images/labs/Attach:servo_motor_control_sch.png

Attch:servo_motor_control_bb.png

 Updated 08 Sep 2009
 by Rory Nugent

 In order to make this work, you must include the Servo.h library file, create an instance of the Servo object. 
 attach a pin to the Servo object, and then write an analog value to the Servo object to set its 

(:div class=code :)

 /*
 Servo control from an analog input using the Arduino Servo library

 This example code uses the Arduino Servo library which comes packaged with the Arduino software.

 In order to make this work, you must include the Servo.h library file, create an instance of the Servo object, 
 attach a digital PWM pin to the Servo object, and then write an analog value to the Servo object to set its 
 position.

 The difference between using the Servo library and the older method of pulsing a digital pin is that the library
 handles a lot of the work for you. You no longer need to figure out the translation between pulse length and position. 
 You now can simply specify the angle you'd like your servo to be at and it will turn to that position.

 Please note, unlike the older pulsing method you MUST use a digital PWM pin or it will not work.


 Created 20 Jan 2009
 by Rory Nugent
 updated 8 Sep 2009
 by Tom Igoe
 */

 #include <Servo.h>      // include the servo library

 Servo servoMotor;       // creates an instance of the servo object to control a servo

 int analogPin = 0;      // the analog pin that the sensor is on
 int analogValue = 0;    // the value returned from the analog sensor

 int servoPin = 2;       // Control pin for servo motor, may only be pin 9 or 10

 void setup() { 
   servoMotor.attach(servoPin);  // attaches the servo on pin 2 to the servo object
 } 

 void loop() 
 { 
   analogValue = analogRead(analogPin);                 // read the analog input (value between 0 and 1023)
   analogValue = map(analogValue, 0, 1023, 0, 179);     // map the analog value (0 - 1023) to the angle of the servo (0 - 179)
   servoMotor.write(analogValue);                       // write the new mapped analog value to set the position of the servo
   delay(15);                                           // waits for the servo to get there 
 }

(:divend:)

 pulseWidth = map(analogValue, 0, 1023, minPulse, maxPulse); 

(:div class=code :)

 /*
  Servo control from an analog input

 The minimum (minPulse) and maxiumum (maxPulse) values
 will be different depending on your specific servo motor.
 Ideally, it should be between 1 and 2 milliseconds, but in practice,
 0.5 - 2.5 milliseconds works well for me.
 Try different values to see what numbers are best for you.

 This program uses the millis() function to keep track of when the servo was
 last pulsed.  millis() produces an overflow error (i.e. generates a number
 that's too big to fit in a long variable) after about 5 days. if you're
 making a program that has to run for more than 5 days, you may need to
 account for this.

 by Tom Igoe
 additions by Carlyn Maw & Rob Faludi
 Created 28 Jan. 2006
 Updated 10 Jun. 2008
 */

 int servoPin = 2;     // Control pin for servo motor
 int minPulse = 500;   // Minimum servo position
 int maxPulse = 2500;  // Maximum servo position
 int pulse = 0;        // Amount to pulse the servo

 long lastPulse = 0;    // the time in milliseconds of the last pulse
 int refreshTime = 20; // the time needed in between pulses

 int analogValue = 0;  // the value returned from the analog sensor
 int analogPin = 0;    // the analog pin that the sensor's on

 void setup() {
  pinMode(servoPin, OUTPUT);  // Set servo pin as an output pin
  pulse = minPulse;           // Set the motor position value to the minimum
  Serial.begin(9600);
 }

 void loop() {
  analogValue = analogRead(analogPin);      // read the analog input
  pulse = map(analogValue,0,1023,minPulse,maxPulse);    // convert the analog value
                                                        // to a range between minPulse
                                                        // and maxPulse.

  // pulse the servo again if rhe refresh time (20 ms) have passed:
  if (millis() - lastPulse >= refreshTime) {
    digitalWrite(servoPin, HIGH);   // Turn the motor on
    delayMicroseconds(pulse);       // Length of the pulse sets the motor position
    digitalWrite(servoPin, LOW);    // Turn the motor off
    lastPulse = millis();           // save the time of the last pulse
  }
 }

(:divend:)

This code was written with a potentiometer in mind, so it assumes you're going to get values from 0 to 1023 from the sensor. If you don't, the servo won't move through its whole range. Determine the range of numbers the sensor is giving you and adjust the servo formula to fit. To fix this, use the map() function. You know the input range is the range of the sensor, 0 to 1023. And you know the output range is from minPulse to maxPulse. So do this:

(:div class=code :)

 pulseWidth = map(sensorValue, 0, 1023, minPulse, maxPulse); 

(:divend:)

Using the Arduino Servo Library

NOTE: If you've just completed the exercise using the pulse method and wish to experiment with the Arduino Servo library you MUST move your servo control pin from digital pin 2 to digital PWM pin 9. A digital PWM pin is needed for the following code to function as expected.

Servo control from an analog input using the Arduino Servo library

This example code uses the Arduino Servo library which comes packaged with the Arduino software.

In order to make this work, you must include the Servo.h library file, create an instance of the Servo object, attach a digital PWM pin to the Servo object, and then write an analog value to the Servo object to set its position.

The difference between using the Servo library and the older method of pulsing a digital pin is that the library handles a lot of the work for you. You no longer need to figure out the translation between pulse length and position. You now can simply specify the angle you'd like your servo to be at and it will turn to that position.

Please note, unlike the older pulsing method you MUST use a digital PWM pin or it will not work.

by Rory Nugent Created 20 Jan. 2009

1. include <Servo.h> // include the servo library

Servo servoMotor; // creates an instance of the servo object to control a servo

int analogPin = 0; // the analog pin that the sensor is on int analogValue = 0; // the value returned from the analog sensor

int servoPin = 9; // Control pin for servo motor, may only be pin 9 or 10

void setup() {

  servoMotor.attach(servoPin);  // attaches the servo on pin 2 to the servo object

}

void loop() {

  analogValue = analogRead(analogPin);                 // read the analog input (value between 0 and 1023)
  analogValue = map(analogValue, 0, 1023, 0, 179);     // map the analog value (0 - 1023) to the angle of the servo (0 - 179)
  servoMotor.write(analogValue);                       // write the new mapped analog value to set the position of the servo
  delay(15);                                           // waits for the servo to get there 

NOTE: If you've just completed the exercise using the pulse method and wish to experiment with the Arduino Servo library you MUST move your servo control pin from digital pin 2 to digital PWM pin 9. A digital PWM pin is needed for the following code to function as expected.

The first example shows you how to control a servo motor using a method that is traditionally taught at ITP which pulses the servo motor with a digital pin to set the position of the servo. This method is more complex and exposes the math and timing required to control a servo with a microcontroller.

(pulseWidth - minPulse) / pulseRange = (sensorValue - minSensorValue) / sensorRange

(pulseWidth - minPulse) = (sensorValue - minsensorValue) * pulseRange / sensorRange

int servoPin = 9; // Control pin for servo motor, may only be pin 9 or 10

Overview

(:title Servo Motor Control with an Arduino:)

In this lab, you'll control a servomotor's position using the value returned from an analog sensor. Servos are the easiest way to start making motion with a microcontroller. Even though they don't turn 360 degrees, you can use them to create all sorts of periodic or reciprocating motions. Check out some of the Flying Pig mechanisms for ideas on how to make levers, cams, and other simple machines for making motion.

(:toc Table of Contents:)

Parts

http://itp.nyu.edu/physcomp/images/labs/servo_sch.png (:cell:) http://itp.nyu.edu/physcomp/uploads/servo_01.jpg

http://itp.nyu.edu/physcomp/uploads/servo_01.jpg | Breadboard version: Arduino connected to a servomotor

http://itp.nyu.edu/physcomp/uploads/servo_01.jpg | Breadboard version: Arduino connected to a servomotor

http://itp.nyu.edu/physcomp/uploads/servo_01.jpg | Breadboard version: Arduino connected to a servomotor

NOTE: If you've just completely the exercise using the pulse method and wish to experiment with the Arduino Servo library you MUST move your servo control pin from digital pin 2 to digital PWM pin 9. A digital PWM pin is needed for the following code to function as expected.

NOTE: If you've just completely the exercise using the pulse method and wish to experiment with the Arduino Servo library you MUST move your servo control pin from digital pin 2 to digital PWM pin 9. A digital PWM pin is needed for the servo library to function.

Using the pulse method

Using the pulse method (without the Arduino Servo library)

Servo servoMotor; // creates an instance of the servo object to control a servo

  servoMotor.write(analogValue);                       // write the new mapped analog value to set the position of the servo

This code was written with a potentiometer in mind, so it assumes you're going to get values from 0 to 1023 from the sensor. If you don't, the servo won't move through its whole range. Determine the range of numbers the sensor is giving you and adjust the servo formula to fit.

The first example shows you how to control a servo motor using a method that is traditionally taught at ITP which pulsed the servo motor with a digital pin to set the position of the servo. This method is more complex and exposes the math and timing required to control a servo with a microcontroller.

The second example shows you how to control a servo motor using the Arduino Servo library. This library is very easy to use and is much easier to follow. However, it obscures all the calculations and handles the dirty work for you. This is useful once you've attempted the pulse method and understand it completely.

The following code examples will move the servo as the value of the sensor changes.

Using the pulse method

The minimum (minPulse) and maxiumum (maxPulse) values

Using the Arduino Servo Library

/*
Servo control from an analog input using the Arduino Servo library

This example code uses the Arduino Servo library which comes packaged with the Arduino software.

In order to make this work, you must include the Servo.h library file, create an instance of the Servo object, 
attach a digital PWM pin to the Servo object, and then write an analog value to the Servo object to set its 
position.

The difference between using the Servo library and the older method of pulsing a digital pin is that the library
handles a lot of the work for you. You no longer need to figure out the translation between pulse length and position. 
You now can simply specify the angle you'd like your servo to be at and it will turn to that position.

Please note, unlike the older pulsing method you MUST use a digital PWM pin or it will not work.

by Rory Nugent
Created 20 Jan. 2009
*/

#include <Servo.h>      // include the servo library

Servo servoMotor;       // create servo object to control a servo

int analogPin = 0;      // the analog pin that the sensor is on
int analogValue = 0;    // the value returned from the analog sensor

int servoPin = 9;       // Control pin for servo motor, must be a PWM pin

void setup() { 
  servoMotor.attach(servoPin);  // attaches the servo on pin 2 to the servo object
} 

void loop() 
{ 
  analogValue = analogRead(analogPin);                 // read the analog input (value between 0 and 1023)
  analogValue = map(analogValue, 0, 1023, 0, 179);     // map the analog value (0 - 1023) to the angle of the servo (0 - 179)
  servoMotor.write(analogValue);                       // sets the servo position with the new mapped value
  delay(15);                                           // waits for the servo to get there 
}

 Servo control from an analog input

The minimum (minPulse) and maxiumum (maxPuluse) values will be different depending on your specific servo motor. Ideally, it should be between 1 and 2 milliseconds, but in practice, 0.5 - 2.5 milliseconds works well for me. Try different values to see what numbers are best for you.

This program uses the millis() function to keep track of when the servo was last pulsed. millis() produces an overflow error (i.e. generates a number that's too big to fit in a long variable) after about 5 days. if you're making a program that has to run for more than 5 days, you may need to account for this.

by Tom Igoe additions by Carlyn Maw & Rob Faludi Created 28 Jan. 2006 Updated 10 Jun. 2008

• /

 pinMode(servoPin, OUTPUT);  // Set servo pin as an output pin
 pulse = minPulse;           // Set the motor position value to the minimum
 Serial.begin(9600);

 analogValue = analogRead(analogPin);      // read the analog input
 pulse = map(analogValue,0,1023,minPulse,maxPulse);    // convert the analog value
                                                       // to a range between minPulse
                                                       // and maxPulse.

 // pulse the servo again if rhe refresh time (20 ms) have passed:
 if (millis() - lastPulse >= refreshTime) {
   digitalWrite(servoPin, HIGH);   // Turn the motor on
   delayMicroseconds(pulse);       // Length of the pulse sets the motor position
   digitalWrite(servoPin, LOW);    // Turn the motor off
   lastPulse = millis();           // save the time of the last pulse
 }

  pulse = (analogValue * 19) / 10 + minPulse;    // convert the analog value

long lastPulse = 0; // the time in milliseconds of the last pulse

 This program uses the millis() function to keep track of when the servo was 
 last pulsed.  millis() produces an overflow error (i.e. generates a number
 that's too big to fit in a long variable) after about 5 days. if you're
 making a program that has to run for more than 5 days, you may need to 
 account for this.

 by Tom Igoe
 additions by Carlyn Maw
 Created 28 Jan. 2006
 Updated 7 Jun. 2006

int lastPulse = 0; // the time in milliseconds of the last pulse int refreshTime = 20; // the time needed in between pulses

  // pulse the servo again if rhe refresh time (20 ms) have passed:
  if (millis() - lastPulse >= refreshTime) {
    digitalWrite(servoPin, HIGH);   // Turn the motor on
    delayMicroseconds(pulse);       // Length of the pulse sets the motor position
    digitalWrite(servoPin, LOW);    // Turn the motor off
    lastPulse = millis();           // save the time of the last pulse
  }

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:

In this lab, you'll control a servomotor's position using the value returned from an analog sensor. Servos are the easiest way to start making motion with a microcontroller. Even though they don't turn 360 degrees, you can use them to create all sorts of periodic or reciprocating motions. Check out some of the Flying Pig mechanisms for ideas on how to make levers, cams, and other simple machines for making motion.

That's the full ranging formula. However, because there are no floating-point variables (i.e. fractions) in the Arduino language (and in most microcontroller languages), you have to fudge the formula a bit. For example, if you have a sensor range from 0 to 512, and a servo range from 500 to 2500 (i.e. a 2000-point range), you know that you can just multiply the servo by 4 and add 500. You'll lose a little detail, but not enough to make a difference to the end user.

When you're making approximations like this, you have to test the approximation at the extremes of both the sensor and the output to make sure it does the job.

That's the full ranging formula. However, because there are no floating-point variables (i.e. fractions) in the Arduino language (and in most microcontroller languages), you have to fudge the formula a bit. For example, if you have a sensor range from 0 to 750, and a servo range from 500 to 2500 (i.e. a 2000-point range), you know that

(pulseWidth - minPulse) / pulseRange = (sensorValue - minSensorValue) /sensorRange

(pulseWidth - minPulse) = (sensorValue - minsensorValue * pulseRange /sensorRange

pulseWidth = ((sensorValue - minSensorValue) * pulseRange / sensorRange) + minPulse

(pulseWidth - minPulse) / pulseRange = (sensorValue - minSensorValue) /sensorRange

(pulseWidth - minPulse) = (sensorValue - minsensorValue * pulseRange /sensorRange

pulseWidth = ((sensorValue - minSensorValue) * pulseRange / sensorRange) + minPulse

Here's a a scaling formula that will make the adjustment:

(pulseWidth - minPulse) / pulseRange = (sensorValue - minSensorValue) /sensorRange

Multiply both sides by pulseRange, and you get:

(pulseWidth - minPulse) = (sensorValue - minsensorValue * pulseRange /sensorRange

Add the minimum pulse to both sides and you get:

pulseWidth = ((sensorValue - minSensorValue) * pulseRange / sensorRange) + minPulse

(:tableend:)

Program the Microcontroller

The following code will move the servo as the value of the sensor changes.

/*
  Servo control from an analog input

 The minimum (minPulse) and maxiumum (maxPuluse) values
 will be different depending on your specific servo motor.
 Ideally, it should be between 1 and 2 milliseconds, but in practice,
 0.5 - 2.5 milliseconds works well for me.
 Try different values to see what numbers are best for you.

 */

int servoPin = 2;     // Control pin for servo motor
int minPulse = 500;   // Minimum servo position
int maxPulse = 2500;  // Maximum servo position
int pulse = 0;        // Amount to pulse the servo

int analogValue = 0;  // the value returned from the analog sensor
int analogPin = 0;    // the analog pin that the sensor's on

void setup() {
  pinMode(servoPin, OUTPUT);  // Set servo pin as an output pin
  pulse = minPulse;           // Set the motor position value to the minimum
  Serial.begin(9600);
}

void loop() {
  analogValue = analogRead(analogPin);      // read the analog input
  pulse = (analogValue / 10) * 19 + 500;    // convert the analog value
                                            // to a range between minPulse
                                            // and maxPulse. 

  Serial.println(pulse, DEC);               // print it out for reference

  digitalWrite(servoPin, HIGH);   // Turn the motor on
  delayMicroseconds(pulse);       // Length of the pulse sets the motor position
  digitalWrite(servoPin, LOW);    // Turn the motor off
  delay(20);                      // 20 millisecond delay is needed between pulses  
                                  // to keep the servo in sync
}

This code was written with a potentiometer in mind, so it assumes you're going to get values from 0 to 1023 from the sensor. If you don't, the servo won't move through its whole range. Determine the range of numbers the sensor is giving youm and adjust the servo formula to fit.

http://itp.nyu.edu/physcomp/images/labs/servo_sch.png

Schematic: http://itp.nyu.edu/physcomp/images/labs/servo_sch.PNG

http://itp.nyu.edu/physcomp/images/labs/bboard_servo.JPG

http://itp.nyu.edu/physcomp/images/labs/bboard_shield_servo.JPG

Connect an analog input sensor and a servo

Pick any analog input and connect it to Analog pin 0 as you did in the Analog Input and Output Lab. Then connect an RC servomotor to digital pin 2. The yellow wire of the servo goes to the pin, and the red and black wires go to +5V and ground, respectively.

(:table:) (:cellnr colspan=2:) schematic (:cellnr:) Breadboard version: http://itp.nyu.edu/physcomp/images/labs/bboard_servo.jpg (:cell:) Breadboard Shield version: http://itp.nyu.edu/physcomp/images/labs/bboard_shield_servo.jpg

http://itp.nyu.edu/physcomp/images/labs/servo.JPG | RC Servomotor

http://itp.nyu.edu/physcomp/images/labs/servo.jpg | RC Servomotor

http://itp.nyu.edu/physcomp/images/labs/flex_sensors.jpg | [-Flex sensors\\

http://itp.nyu.edu/physcomp/images/labs/flex_sensors.jpg | RC Servomotor

In this lab, you'll control a servomotor's position using the value returned from an analog sensor.

For this lab you'll need:

http://itp.nyu.edu/physcomp/images/labs/breadboard.jpg | Solderless breadboard http://itp.nyu.edu/physcomp/images/labs/hookup_wire.jpg | 22-AWG hookup wire http://itp.nyu.edu/physcomp/images/labs/arduino.jpg | Arduino Microcontroller
module

http://itp.nyu.edu/physcomp/images/labs/resistors.jpg | 10Kohm resistors http://itp.nyu.edu/physcomp/images/labs/potentiometer.jpg | 10Kohm potentiometer Variable resistors http://itp.nyu.edu/physcomp/images/labs/flex_sensors.jpg | Flex sensors
(or a different
form of variable resistor)

Prepare the breadboard

Conect 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:

http://itp.nyu.edu/physcomp/images/labs/arduino_bboard_power.jpg

If you're using an Arduino breadboard shield, there is a row of sockets connected to 5V on the analog in side of the breadboard, and a row connected to ground on the digital in side of the board:

http://itp.nyu.edu/physcomp/images/labs/breadboard_shield.jpg

In this lab, you'll control a servomotor's position using the value returned from an analog sensor.