Arduino
Week 2 Lab
ECE 1020
Prof. Ahmadi
Objectives
1.
Control the rotation of standard servo motor

2.
A standard servo motor is limited in its rotation
between 0 and 180 degrees
Control the speed of a continuous rotation servo
motor based on the light intensity

A continuous rotation servo motor can rotate freely
without restriction
Introduction to Servos
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A servo is a small, electrically-driven motor that provides
rotary actuation
Servos are controlled by using Pulse-Width Modulation
(PWM)
The duration of a voltage pulse determines how far the
shaft will turn (i.e. the angle)
Servos will not hold their position indefinitely, so the
position pulse must be sent repeatedly
The holding force of a servo is determined by it’s torque
rating
PWM Generation
 There
are 2 different ways in which you can
generate a PWM signal
1.
2.
Use the built-in PWM pins on the Arduino where you
only need to set the duty cycle
Manually generate one by alternating voltage HIGH
and LOW with specified delays
 We
will use the manual method since the built-in
PWM frequency does not match the servo’s
expected pulse timing
Part 1 – Controlling Servo
Rotation (Manual PWM)
int servoPin = 4;
int pulse = 700;
void setup()
{
pinMode(servoPin, OUTPUT);
Serial.begin(9600);
}
void loop()
{
digitalWrite(servoPin, HIGH);
delayMicroseconds(pulse);
digitalWrite(servoPin, LOW);
delay(20);
}
//variable to store the servo pin number
//variable to store the pulse duration
//set the servo pin as an output
//set serial data transfer rate
//send 5V to the servo
//for pulse microseconds
//send 0V to the servo
//for 20 milliseconds
You can change the duration of the pulse to vary the servo’s rotation angle.
Part 1 Schematic (Manual
PWM)
Standard servo
Part 1 Board Layout
Servo
motor
Pin 4
5V
Ground
Servo
connector
How to read a light sensor
[What is a light sensor?]
 The
light sensor we are using is the same one we
used when working with the Lego Botball robotics
kit.
 Light sensor is a photoresistor, also known as a light
dependent resistor.
 A photoresistor is a sensor whose resistance varies
with light intensity. Most decrease in resistance as
the light intensity increases.
How to read a light sensor
[How to connect it?]
 The
sensor is connected in series with a resistor
 Both of which are between the +5V terminal of the
Arduino and the Ground terminal
 They form a Voltage Ladder
 The data we want comes from the voltage at the
point of connection between the sensor and
resistor [This is what will change in response to light]
Reading the Light Sensor
int sensorPin = A0;
int sensorValue = 0;
void setup()
{
Serial.begin(9600);
}
void loop()
//variable to set the sensor input pin
//set serial data transfer rate
{
sensorValue = analogRead(sensorPin); //read the value from the light sensor
Serial.print ("Sensor value = "); //print the sensor value to the computer screen
Serial.print(sensorValue);
Serial.println(";");
//"printLN" creates a new line
}
On your keyboard, press “Ctrl+Shift+M” after uploading your program to open the
serial communication dialog.
Light Sensor Schematic
Board Layout
Pin A0
Light sensor
5V
Light sensor connector
Resistor
Ground
Now let’s combine the light
sensor with a servo motor to
build a light-sensitive servo that
rotates at speeds proportional
to the light intensity.
Part 2 – Controlling Servo Rotation Speed
as a Function of Light Intensity (1)
int sensorPin = A0;
int outPin = 5;
int sensorValue = 0;
int m = 0;
void setup()
{
Serial.begin(9600);
pinMode(outPin, OUTPUT);
}
//variable to set the sensor input pin
//variable to store the output pin
//variable to store the value coming from the sensor
//variable to store the motor signal (i.e. the voltage)
//voltage controls the speed of a continuous servo
//set serial data transfer rate
//set the output pin as an output
Continued on next slide…
Part 2 – Controlling Servo Rotation Speed
as a Function of Light Intensity (2)
void loop()
{
sensorValue = analogRead(sensorPin);
Serial.print ("Sensor value = ");
Serial.print(sensorValue);
Serial.print(";");
m = map(sensorValue, 0, 1023, 0, 255);
analogWrite(outPin, m);
}
Serial.print ("m = ");
Serial.print(m);
Serial.println(";");
//read the value from the light sensor
//print the sensor value to the computer screen
//convert sensorValue to motor signal
//PWM output is from 0-255
//send the motor signal to the servo
//print the motor signal to the computer screen
Part 2 Schematic
Continuous rotation servo
Part 2 Board Layout
Light sensor connector
Light sensor
Servo
connector
Servo
motor
Pin A0
5V
Resistor
Pin 5
Ground
Command Reference
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pinMode(pin,mode) – configures the pin to behave either as an
input or an output
Serial.begin(speed) – sets the data transfer rate for serial
communication
digitalWrite(pin,value) – sets the specified pin’s voltage to HIGH
(5V) or LOW (0V)
delay(ms) – pauses the program for the specified amount of
time in milliseconds
analogRead(pin) – reads the value from the specified pin; maps
voltage from 0V to 5V into integer values between 0 and 1023
map(value, fromLow, fromHigh, toLow, toHigh) – maps the
values in the from range to the to range
Serial.print() – writes data to the computer in ASCII text format
http://arduino.cc/en/Reference/HomePage