Beginning Arduino by Michael McRoberts

Author:Michael McRoberts
Language: eng
Format: mobi, epub, pdf
Publisher: Apress
Published: 2011-02-16T14:54:13.201109+00:00

Servo servo1; // Create a servo object

193

CHAPTER 9 ■ SERVOS

void setup()

{

servo1.attach(5); // Attaches the servo on Pin 5 to the servo object

}

void loop()

{

int angle = analogRead(0); // Read the pot value

angle=map(angle, 0, 1023, 0, 180); // Map the values from 0 to 180 degrees

servo1.write(angle); // Write the angle to the servo

delay(15); // Delay of 15ms to allow servo to reach position

}

Project 25 – Servo Control – Code Overview

First, the Servo.h library is included:

#include <Servo.h>

Then a Servo object called servo1 is declared:

Servo servo1; // Create a servo object

In the setup loop, you attach the servo you have just created to Pin 5:

servo1.attach(5); // Attaches the servo on Pin 5 to the servo object

The attach command attaches a created servo object to a designated pin. The attach command can

take either one parameter, as in your case, or three parameters. If three parameters are used, the first

parameter is the pin, the second is the minimum (0 degree) angle in pulse width in microseconds

(defaults to 544), and the third parameter is the maximum degree angle (180 degrees) in pulse width in

microseconds (defaults to 2400). This will be explained in the hardware overview. For most purposes you

can simply set the pin and ignore the optional second and third parameters.

You can connect up to 12 servos to an Arduino Duemilanove (or equivalent) and up to 48 on the

Arduino Mega—perfect for robotic control applications!

Note that using this library disables the analogWrite (PWM) function on Pins 9 and 10. On the Mega

you can have up to 12 motors without interfering with the PWM functions. The use of between 12 and 23

motors will disable the PWM functionality on Pins 11 and 12.

In the main loop, read the analog value from the potentiometer connected to Analog Pin 0:

int angle = analogRead(0); // Read the pot value

Then that value is mapped so the range is now between 0 and 180, which will correspond to the

degree angle of the servo arm:

angle=map(angle, 0, 1023, 0, 180); // Map the values from 0 to 180 degrees

Then you take your servo object and write the appropriate angle, in degrees, to it (the angle must be

between 0 and 180 degrees):

194

CHAPTER 9 ■ SERVOS

servo1.write(angle); // Write the angle to the servo

Finally, a delay of 15ms is programmed to allow the servo time to move into position:

delay(15); // Delay of 15ms to allow servo to reach position

You can also detach() a servo from a pin, which will disable it and allow the pin to be used for

something else. Also, you can read() the current angle from the servo (this is the last value passed to the

write() command).

You can read more about the Servo library on the Arduino website athttp://arduino.cc/

en/Reference/Servo.

Project 25 – Servo Control – Hardware Overview

A servo is a little box that contains a DC electric motor, a set of gears between the motor and an output

shaft, a position sensing mechanism, and the control circuit. The position sensing mechanism feeds

back the servo’s position to the control circuitry, which uses the motor to adjust the servo arm to the

position that the servo should be at.

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