Arduino Week 2 LabECE 1020Prof. Ahmadi

Objectives

1. Control the rotation of standard servo motor A standard servo motor is limited in its rotation

between 0 and 180 degrees

2. 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 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 signal1. Use the built-in PWM pins on the Arduino where

you only need to set the duty cycle2. 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; //variable to store the servo pin numberint pulse = 700; //variable to store the pulse duration

void setup(){

pinMode(servoPin, OUTPUT); //set the servo pin as an outputSerial.begin(9600); //set serial data transfer rate

}

void loop(){

digitalWrite(servoPin, HIGH); //send 5V to the servodelayMicroseconds(pulse); //for pulse microsecondsdigitalWrite(servoPin, LOW); //send 0V to the servodelay(20); //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

Ground

5V

Pin 4

Servoconnector

Servomotor

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 Sensorint sensorPin = A0; //variable to set the sensor input pinint sensorValue = 0;void setup(){ Serial.begin(9600); //set serial data transfer rate}void loop()

{ 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

Light sensor

5VPin A0

Ground

Light sensor connector

Resistor

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; //variable to set the sensor input pinint outPin = 5; //variable to store the output pinint sensorValue = 0; //variable to store the value coming from the sensorint m = 0; //variable to store the motor signal (i.e. the voltage)

//voltage controls the speed of a continuous servo

void setup(){ Serial.begin(9600); //set serial data transfer rate pinMode(outPin, OUTPUT); //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); //read the value from the light sensor Serial.print ("Sensor value = "); //print the sensor value to the computer screen Serial.print(sensorValue); Serial.print(";"); m = map(sensorValue, 0, 1023, 0, 255); //convert sensorValue to motor signal

//PWM output is from 0-255 analogWrite(outPin, m); //send the motor signal to the servo Serial.print ("m = "); //print the motor signal to the computer screen Serial.print(m); Serial.println(";"); }

Part 2 Schematic

Continuous rotation servo

Part 2 Board Layout

Light sensor

Servo connector

5VPin A0

GroundPin 5

Light sensor connector

Servo motor

Resistor

Command Reference 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

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