CIRC
04

What We're Doing

Spinning a motor is good fun but when it comes to projects where motion control is required they tend to leave us wanting more. The answer? Hobby servos. They are mass produced, widely available and cost anything from a couple of dollars to hundreds. Inside is a small gearbox (to make the movement more powerful) and some electronics (to make it easier to control). A standard servo is positionable from 0 to 180 degrees. Positioning is controlled through a timed pulse, between 1.25 milliseconds (0 degrees) and 1.75 milliseconds (180 degrees) (1.5 milliseconds for 90 degrees). Timing varies between manufacturer. If the pulse is sent every 25-50 milliseconds the servo will run smoothly. One of the great features of the Arduino is it has a software library that allows you to control two servos (connected to pin 9 or 10) using a single line of code.

CAUTION: Not all servos have the same connector or wire colours. If you are using a different brand of servo, double (and triple) check how it is wired before you start. You CAN damage the servo by connecting it incorrectly. A place to start for checking servo connector wiring is Servo City https://www.servocity.com/servo-connector-types.

The Circuit

The Parts

	CIRC-04 Breadboard Sheet x1		2 Pin Header x4		3 Pin Header x1		Wire
	Mini Servo x1

Code (no need to type everything in just)

File > Examples > Servo > Sweep

(example from the great arduino.cc site, check it out for other ideas)

// Sweep
// by BARRAGAN

#include <Servo.h>

Servo myservo;  // create servo object to control a servo
                // a maximum of eight servo objects can be created

int pos = 0;    // variable to store the servo position

void setup()
{
  myservo.attach(9);  // attaches the servo on pin 9 to the servo object
}


void loop()
{
  for(pos = 0; pos < 180; pos += 1)  // goes from 0 degrees to 180 degrees
  {                                  // in steps of 1 degree
    myservo.write(pos);              // tell servo to go to position in variable 'pos'
    delay(15);                       // waits 15ms for the servo to reach the position
  }
  for(pos = 180; pos>=1; pos-=1)     // goes from 180 degrees to 0 degrees
  {
    myservo.write(pos);              // tell servo to go to position in variable 'pos'
    delay(15);                       // waits 15ms for the servo to reach the position
  }
}

Not Working? (3 things to try)

Making it Better?

Potentiometer Control:

We have yet to experiment with inputs but if you would like to read ahead, there is an example program File > Library-Servo > Knob. This uses a potentiometer (CIRC08) to control the servo. You can find instructions online here: http://ardx.org/KNOB

Self Timing:

While it is easy to control a servo using the Arduino's included library sometimes it is fun to figure out how to program something yourself. Try it. We're controlling the pulse directly so you could use this method to control servos on any of the Arduino's 20 available pins (you need to highly optimize this code before doing that).

int servoPin = 9;

void setup() {
  pinMode(servoPin,OUTPUT);
}

void loop() {
  int pulseTime = 2100; //(the number of microseconds
                        //to pause for (1500 90 degrees
                        // 900 0 degrees 2100 180 degrees)
  digitalWrite(servoPin, HIGH);
  delayMicroseconds(pulseTime);
  digitalWrite(servoPin, LOW);
  delay(25);
}

Great Ideas:

Servos can be used to do all sorts of great things, here are a few of our favourites.

Xmas Hit Counter

http://ardx.org/XMAS

Open Source Robotic Arm (uses a servo controller as well as the Arduino)

http://ardx.org/RARM

Servo Walker

http://ardx.org/SEWA