Wall Avoidance

Introduction

Sparki can use its ultrasonic sensor to avoid running into walls. In this lesson you will program Sparki to do just that!

What You’ll Need

A Sparki.
Some space for it to run around in and some walls. You can also use solid objects like cardboard boxes for your walls. Try to have hard walls (instead of soft things like pillows or cloth) since the ultrasonic range finder thinks those are easier to see.

How It Works

Here is the ultrasonic sensor or ultrasonic range finder. Sparki uses it to see what is in front of it in a similar way to how a dolphin or a bat uses echolocation. If you are not familiar with this sensor, please read this previous lesson.

Also, please remember (you can find more information here) that this sensor has a conic detection zone, like this:

Please remember to check that the batteries are properly connected (and charged!). And as we are going to use the motors here, please check that the On/Off Switch is on. Another important thing to take care of when playing with the robot’s motors is to be careful not to be working over a table. A fall from that table could permanently damage your Sparki. In this example, we’re going to code up something where Sparki will wander with a green light on (using its RGB LED) until it finds a wall is shortly ahead of it. Sparki then puts on the red light, moves backward, turns, puts the LED back to green, and then continues on. These are the basic tasks that we want the robot to do in order to advance while avoiding obstacles:

Center the ultrasonic sensor so it points to the front.
Change the color of the LED to green.
Make Sparki go forward.
Sense distance with the rangefinder.
When Sparki’s rangefinder finds an obstacle:
- Make Sparki beep using the buzzer.
- Change the LED to red.
- Make Sparki move backward.
- Make Sparki turn.

Coding the Wall Avoidance Program

Now that we know what to do, let’s figure out how to do it. Looking at the parts list we can look up how to do the following things and find the following codes:

Center the ultrasonic sensor so it points to the front:

sparki.servo(SERVO_CENTER);

1	sparki.servo(SERVO_CENTER);

Change the color of the LED to green:

sparki.RGB(RGB_GREEN);

1	sparki.RGB(RGB_GREEN);

Make Sparki go forward:

sparki.moveForward()

1	sparki.moveForward()

Sense distance with the rangefinder:

sparki.ping();

1	sparki.ping();

Make Sparki beep:

sparki.beep();

1	sparki.beep();

Change the LED to red:

sparki.RGB(RGB_RED);

1	sparki.RGB(RGB_RED);

Make Sparki move backward:

sparki.moveBackward(10)

1	sparki.moveBackward(10)

Make Sparki turn:

sparki.moveRight(30);

1	sparki.moveRight(30);

Putting pieces together, we can make chunks of commands which represent what Sparki normally does and what Sparki does when it finds a wall. Normally, we want the robot to:

Change the color of the LED to green.
Go forward.

Code for this looks like:

sparki.moveForward(); // move forward
sparki.RGB(RGB_GREEN); // turn the light green

1 2	sparki.moveForward(); // move forward sparki.RGB(RGB_GREEN); // turn the light green

And the commands for the chunk when it detects the wall or obstacle are:

Make the LED red
Beep
Move backward
Turn

Which translated into code reads like:

sparki.RGB(RGB_RED); // turn the light red
sparki.beep(); // beep!
sparki.moveBackward(10); // back up 10 centimeters
sparki.moveRight(30); // rotate right 30 degrees

sparki.RGB(RGB_RED); // turn the light red

sparki.beep(); // beep!

sparki.moveBackward(10); // back up 10 centimeters

sparki.moveRight(30); // rotate right 30 degrees

Now let’s look at what that looks like when we put it all together! Remember that we want the robot to make decisions, so we have wrapped large parts of the code in if statements and only triggers under the right conditions. We have also added a delay before the robot checks the distance again. This is because Sparki’s brain is much faster than its wheels, so there is no use in checking again until the robot has moved a bit:

#include <Sparki.h> // include the sparki library

void setup()
{
    sparki.servo(SERVO_CENTER); // Center the Servo
}

void loop()
{
    sparki.RGB(RGB_GREEN); // turn the light green
    sparki.moveForward(); // move Sparki forward
    int cm = sparki.ping(); // measures the distance with Sparki's eyes

    if(cm != -1) // make sure its not too close or too far
    { 
        if(cm < 20) // if the distance measured is less than 20 centimeters
        {
            sparki.RGB(RGB_RED); // turn the light red
            sparki.beep(); // beep!
            sparki.moveBackward(10); // back up 10 centimeters
            sparki.moveRight(30); // rotate right 30 degrees
            delay(1000);
        }
    }
    delay(100); // wait 0.1 seconds (100 milliseconds)
}

#include <Sparki.h> // include the sparki library

void setup()

{

sparki.servo(SERVO_CENTER); // Center the Servo

}

void loop()

{

sparki.RGB(RGB_GREEN); // turn the light green

sparki.moveForward(); // move Sparki forward

int cm = sparki.ping(); // measures the distance with Sparki's eyes

if(cm != -1) // make sure its not too close or too far

{

if(cm < 20) // if the distance measured is less than 20 centimeters

{

sparki.RGB(RGB_RED); // turn the light red

sparki.beep(); // beep!

sparki.moveBackward(10); // back up 10 centimeters

sparki.moveRight(30); // rotate right 30 degrees

delay(1000);

}

delay(100); // wait 0.1 seconds (100 milliseconds)

}

Now you’ve made Sparki avoid walls and obstacles!

Related Lessons

To learn more about the ultrasonic range finder, take a look at the following lessons:

Using the Ultrasonic Distance Sensor
Theremin
Also, a similar technique but with different sensors is used in the Edge Avoidance lesson.

Lesson available for the miniBloq Programming Environment

This lesson is also available for the miniBloq Programming Environment. miniBloq is a graphical programming environment that you can use to easily program your Sparki.

Getting Started

Basic miniBloq

How to Code

Basic SparkiDuino

Advanced SparkiDuino

Sparki + Android