Arduino Week 2 Lab ECE 1020 Prof. Ahmadi

Objectives Control the rotation of standard servo motor 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 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 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; //variable to store the servo pin number int pulse = 700; //variable to store the pulse duration void setup() { pinMode(servoPin, OUTPUT); //set the servo pin as an output Serial.begin(9600); //set serial data transfer rate } void loop() digitalWrite(servoPin, HIGH); //send 5V to the servo delayMicroseconds(pulse); //for pulse microseconds digitalWrite(servoPin, LOW); //send 0V to the servo delay(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 Servo motor Pin 4 5V Servo connector Ground

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; //variable to set the sensor input pin int 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 5V Pin A0 Light sensor 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; //variable to set the sensor input pin int outPin = 5; //variable to store the output pin int sensorValue = 0; //variable to store the value coming from the sensor int 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(";"); analogWrite(outPin, 50); //send pulse to servo delay(200); //constant high pulse duration analogWrite(outPin, 0); delay(sensorValue); //low pulse duration changes according to sensor reading }

Part 2 Schematic Continuous rotation servo

Part 2 Board Layout Light sensor connector Light sensor Pin A0 5V Servo connector Resistor Servo motor Pin 5 Ground

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 http://arduino.cc/en/Reference/HomePage