Movement in Modes

Eduator Intro

Length of the chapter: 1,5 - 3h

Adjust the time according to your schedule and goals Check out the lesson plan options below!

Learning Objectives

Students will learn…

• …to connect a servo motor
• …to use the servo library to program servo motors
• …to program the toggle functionality by following instructions: tracking button presses, activating things when a button is pressed and released after that
• …new ways to make use of digital logic: using the NOT sign ( ! ) in conditions and to flip values to their opposites

Depending on the final exercise, the students also practice…

• … creating a mechanism for the servo by making a small creeper robot or a moving mechanic prototype (Exercise 1: Mad Mechanisms)
• … to code a servo to turn towards light using inputs from two LDR sensors (Exercise 2: Light Follower)

Slides and Lesson PLans

Feel free to use these slides to introduce the third chapter to the students!

There are some speaker notes attached to the slides. To see the speaker notes, click Options > Open Speaker Notes in the bottom panel.

Lesson plan suggestion

Total: 90-130 min

There are a lot of code examples in the educator notes throughout this page - we hope it’s useful! You’ll be able to assist the students in every phase of this task using these code examples.

What if the time is running out?

Skip Programming 5 - Signal Lights if you have a tight schedule!

Key points:

• including the servo library in the code, creating a servo object
• setting the servo pin up with myServo.attach
• moving the servo back and forth with myServo.write

Example code

//include the servo library:
#include <Servo.h>
//create a servo object and name it myServo:
Servo myServo;

void setup() {
  //tell the Arduino that myServo is attached to pin 11
  myServo.attach(11);
}

void loop() {
  //move the servo to an angle (0-180) with write command:
  myServo.write(20);
  //add a delay:
  delay(500);
  //move the servo to a new angle:
  myServo.write(170);
  //add a delay:
  delay(1000); 
}

What if the servo doesn’t move?

• With very small delay values the motor may not move at all. In this case, the program may be executed so fast the servo motor doesn’t have time to move from one position to another!
• If the student’s code is written as above, suggest they check the connections on the breadboard.
• On rare occasions the servo motor may be broken. The plastic gears may break if you turn the servo manually.

Key points:

• “commenting out” a chunk of code to save it for later use
• mapping the value from the potentiometer to a servo angle

Example code

#include <Servo.h>
Servo myServo;

//create integer variable potValue:
int potValue;
//create integer variable angle:
int angle;

void setup() {
  myServo.attach(11);
}

void loop() {
  /* 
  myServo.write(20); 
  delay(500); 
  myServo.write(170); 
  delay(1000); 
  */

  //read the value from A0 and store to potValue:
  potValue = analogRead(A0);
  //give variable angle a value: map it from potValue:
  angle = map(potValue, 0, 1023, 0, 180);
  //move the servo with angle as parameter:
  myServo.write(angle);
  //delay of 50ms:
  delay(50);

}

Key point:

• learning to compare the state of the button between two loop runs

Example Code

#include <Servo.h>
Servo myServo;
int potValue;
int angle;
//create an integer variable to store the button state now:
int buttonState;
//create an integer variable to store the button state in the last loop run:
int lastButtonState;

void setup() {
  myServo.attach(11);
  //define pin 3 as input pullup:
  pinMode(3, INPUT_PULLUP);
  //start serial communication:
  Serial.begin(9600);
}

void loop() {
  //store the current state of the button:
  buttonState = digitalRead(3);
  //print the current state of the button:
  Serial.println(buttonState);
  //check if the current button state is the same as last round:
  if(buttonState != lastButtonState) {
    //if the state isn't the same, print this:
    Serial.println("Hey it changed!");
  }
  /*
  myServo.write(20);
  delay(500);
  myServo.write(170);
  delay(1000); 
  */
  potValue = analogRead(A0);
  angle = map(potValue, 0, 1023, 0, 180);
  myServo.write(angle);
  delay(50);
  
  // store the button state to lastButtonState:
  lastButtonState = buttonState;

}

Key points:

• using a variable (servoMode) to define different servo modes
• defining with if statements what happens when servoMode gets values 0 or 1
• changing the servoMode value when the button is pressed and released
• It’s a good idea to add some Serial.print / Serial.println commands to the code, especially if something is wrong and it’s hard to tell what it is! Print for example the servoMode variable if the mode doesn’t change, or the potValue if the manual mode doesn’t work well.

Example code

#include <Servo.h>
Servo myServo;
int potValue;
int angle;
int buttonState;
int lastButtonState;
//integer variable for storing the servo mode, initial value 1:
int servoMode = 1; //manual: 1, sweep: 0

void setup() {
  myServo.attach(11);
  pinMode(3, INPUT_PULLUP);
  Serial.begin(9600);
}

void loop() {
  buttonState = digitalRead(3);
  Serial.println(buttonState);
  
  if(buttonState != lastButtonState) {
    if(buttonState == 1) {    //if the button is up
      servoMode = !servoMode; //flip the value to its opposite
    }
  } 
  
  if (servoMode == 0) { //if servoMode is 0, go to sweep mode
    myServo.write(20);
    delay(500);
    myServo.write(170);
    delay(1000); 
  } else {             //else go to manual mode (servoMode is 1)  
    potValue = analogRead(A0);
    angle = map(potValue, 0, 1023, 0, 180);
    myServo.write(angle);
    delay(50);
  }
  
  lastButtonState = buttonState;
}

Key point:

• signaling with LED lights when the servo mode is about to change (when the button is pressed down)
• If you’re running out of time, this phase can be skipped.

The Final Code

#include <Servo.h>
Servo myServo;
int potValue;
int angle;
int buttonState;
int lastButtonState;
int servoMode = 1; //manual: 1, sweep: 0

void setup() {
  myServo.attach(11);
  pinMode(3, INPUT_PULLUP);
  //define pins 6 and 9 as outputs:
  pinMode(6, OUTPUT);
  pinMode(9, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  buttonState = digitalRead(3);
  Serial.println(buttonState);
  
  if(buttonState != lastButtonState) {
    //use digitalWrite to turn one LED on and the other off.
    //instead of HIGH or LOW, use servoMode and !servoMode as parameters
    digitalWrite(6, servoMode);
    digitalWrite(9, !servoMode);
    if(buttonState == 1) {    //if the button is up
      servoMode = !servoMode; //flip the value to its opposite
    }
  } 
  
  if (servoMode == 0) { //if servoMode is 0, go to sweep mode
    myServo.write(20);
    delay(500);
    myServo.write(170);
    delay(1000); 
  } else {             //else go to manual mode (servoMode is 1)  
    potValue = analogRead(A0);
    angle = map(potValue, 0, 1023, 0, 180);
    myServo.write(angle);
    delay(50);
  }
  
  lastButtonState = buttonState;
}

Learn More: Motors & Power

You might have problems with servo motors due to insufficient voltage or current. The current may be too weak especially if:

• You're using multiple servos at the same time.
• You're using for example a 9 V battery to power up the Arduino.

You'll notice the lack of power when the servo doesn't rotate smoothly.. Here are a couple of hints on how you can guarantee your servo receives enough current:

Use a separate power supply for the servos

An option is to use a separate power supply for the servos. The servos usually work with a voltage of 4-6 V (Arduino provides 5 V). For example, 4 AA batteries provide a voltage of 6 V, which is enough for multiple servos (4 x 1.5 V = 6 V).

In the picture, Arduino uses a voltage of 9 volts, while the servos use a voltage of 6 volts! Arduino's processor runs on a different power supply than the servos, which diminishes the load on the 9 V battery. The positive terminal of the 4-battery-pack has been connected to the servos' voltage wire and the ground terminal to servos' ground wire and to Arduino's ground. You can still use a USB cable to connect Arduino to the computer, which will then take care of powering up the board.

Use a mobile phone powerbank

A powerbank can easily be connected to Arduino, because it has a USB connection. The lifetime of the battery is at least 2500 mAh, when the lifetime of a 9 V battery is usually only about 500 mAh. At best, a powerbank can provide power to both an Arduino and the servos connected to it.

Use a power supply which connects to a power socket

Learn more about external power supplies for example on the Arduino website