Program the Crab Bot

You've built the Crab Bot. Learn how to program the sensors to detect light, and then use variables, if statements, and loops to program the Crab Bot to move away from light, just like a nocturnal crab. You can also learn how to program the Smart Inventor Board's LEDs.
Crab robot cover Crab robot cover

This lesson works with:

Rokit Smart
Arduino
  • arduino
  • computer science
  • Crab
  • programming
  • robotics
  • Rokit Smart
  • sensors

Grade level:

3 - 12+

Approx. time required:

30 - 45 mins
CSTA

1B-AP-10

3-5

Create programs that include sequences, events, loops, and conditionals.

1B-CS-03

3-5

Determine potential solutions to solve simple hardware and software problems using common troubleshooting strategies.

1B-IC-20

3-5

Seek diverse perspectives for the purpose of improving computational artifacts.

2-CS-01

6-8

Recommend improvements to the design of computing devices, based on an analysis of how users interact with the devices.

2-CS-03

6-8

Systematically identify and fix problems with computing devices and their components.
NGSS

3-5-ETS1-3 Science

Grade 4

Plan and carry out fair tests in which variables are controlled and failure points are considered to identify aspects of a model or prototype that can be improved.

4-PS3-4 Science

Grade 4

Apply scientific ideas to design, test, and refine a device that converts energy from one form to another.
CCSS

CCSS.ELA-Literacy.RI.3.7 Language Arts

Grade 3

Use information gained from illustrations (e.g., maps, photographs) and the words in a text to demonstrate understanding of the text (e.g., where, when, why, and how key events occur).

Read More

CCSS.ELA-Literacy.RI.3.8 Language Arts

Grade 3

Describe the logical connection between particular sentences and paragraphs in a text (e.g., comparison, cause/effect, first/second/third in a sequence).

Read More

CCSS.ELA-Literacy.RI.4.7 Language Arts

Grade 4

Interpret information presented visually, orally, or quantitatively (e.g., in charts, graphs, diagrams, time lines, animations, or interactive elements on Web pages) and explain how the information contributes to an understanding of the text in which it appears.

Read More

CCSS.ELA-Literacy.RI.5.7 Language Arts

Grade 5

Draw on information from multiple print or digital sources, demonstrating the ability to locate an answer to a question quickly or to solve a problem efficiently.

Read More

CCSS.ELA-Literacy.RI.6.7 Language Arts

Grade 6

Integrate information presented in different media or formats (e.g., visually, quantitatively) as well as in words to develop a coherent understanding of a topic or issue.

Read More

CCSS.ELA-LITERACY.RST.6-8.3 Language Arts

6-8

Follow precisely a multistep procedure when carrying out experiments, taking measurements, or performing technical tasks. 

CCSS.ELA-Literacy.RST.6-8.7 Language Arts

Grade 8

Integrate quantitative or technical information expressed in words in a text with a version of that information expressed visually (e.g., in a flowchart, diagram, model, graph, or table).

Read More

CCSS.Math.Practice.MP1 Math

High School — Geometry

Make sense of problems and persevere in solving them.

Read More

CCSS.Math.Practice.MP5 Math

Grade 3

Use appropriate tools strategically.

Read More

CCSS.Math.Practice.MP7 Math

Grade 5

Look for and make use of structure.

Read More
Step 1

Briefing videos

These videos go over how to program your Crab Bot. Don’t forget to go through the rest of the lesson!

Step 2

What does it do?

Just like the nocturnal crabs you might have seen at the beach, the Crab Bot is programmed to avoid light! If any of its sensors detect light, the Crab Bot will move away from the light source.

This is the Crab Bot’s pseudocode:

  • Check the top left, center, and right IR sensors
  • If the light is shining from the left, move to the right.
  • Else, if the light is shining from the right, move to the left.
  • Else, if the light is shining from the center, move back and forth.
  • Else, stop.
Step 3

Set up the motors

The first thing you need to do is include the Smart Inventor library at the top of your code. Next, in void setup(), include your motors.

#include <SmartInventor.h>

void setup() {
    SmartInventor.DCMotorUse();
}
Step 4

Base level of the sensors

Each sensor corresponds to a pin on the Smart Inventor Board, and those need to be read for anything to happen with your Crab Bot! Underneath the Smart Inventor library and before void setup(), set variables for each sensors’ base values. Use those variables in void setup() so the sensors will know if they’re seeing a value that isn’t normal. Add a buffer of 50 to leave some room for error.

#include <SmartInventor.h>

int leftBaseLevel;
int centerBaseLevel;
int rightBaseLevel;
 
void setup() {
    SmartInventor.DCMotorUse();
    
    leftBaseLevel = analogRead(19) - 50;
    centerBaseLevel = analogRead(20) - 50;
    rightBaseLevel = analogRead(21) - 50;
}
Step 5

Read the sensors

In void loop(), set variables for each sensor so that they get and save the value that is being read from their corresponding pin.

#include <SmartInventor.h> 
int leftBaseLevel;
int centerBaseLevel;
int rightBaseLevel;
 
void setup() {
    SmartInventor.DCMotorUse();

    leftBaseLevel = analogRead(19) - 50;
    centerBaseLevel = analogRead(20) - 50;
    rightBaseLevel = analogRead(21) - 50;
}
 
void loop() {
    int leftSensor = analogRead(19);
    int centerSensor = analogRead(20);
    int rightSensor = analogRead(21);
}
Step 6

Left sensor

Next up: the main section of the code! You’ll need to use an if statement to check if the left sensor has detected any light. This would bring the value of the left sensor lower than the value of its base level. If the left sensor detects light, the left LEDs will light up and the Crab Bot will move to the right.

void loop() {
    int leftSensor = analogRead(19);
    int centerSensor = analogRead(20);
    int rightSensor = analogRead(21);

    if(leftSensor < leftBaseLevel)
    {
        digitalWrite(11, HIGH); // light the left LEDs
        digitalWrite(15, HIGH);
        digitalWrite(12, LOW);
        digitalWrite(17, LOW);
        digitalWrite(13, LOW);
        digitalWrite(18, LOW);

    SmartInventor.DCMotor(M1, CCW, 50); // move right
    }
}
Step 7

Right sensor

You’re going to do the same thing for the right sensor, but you’ll need to use an else if statement instead of an if statement. This means that your code will only check it if the last if statement about the left sensor was false.

void loop() {    
    int leftSensor = analogRead(19);    
    int centerSensor = analogRead(20);    
    int rightSensor = analogRead(21);    

    if(leftSensor < leftBaseLevel)    {        
        digitalWrite(11, HIGH); // light the left LEDs        
        digitalWrite(15, HIGH);        
        digitalWrite(12, LOW);        
        digitalWrite(17, LOW);        
        digitalWrite(13, LOW);        
        digitalWrite(18, LOW);    

        SmartInventor.DCMotor(M1, CCW, 50); // move right 
    }   
    else if(rightSensor < rightBaseLevel)
    {
        digitalWrite(11, LOW); // light the right LEDs
        digitalWrite(15, LOW);
        digitalWrite(12, LOW);
        digitalWrite(17, LOW);
        digitalWrite(13, HIGH);
        digitalWrite(18, HIGH);

    SmartInventor.DCMotor(M1, CW, 50); // move right
    }
}
Step 8

Center sensor

Add another else if statement so that when the center sensor detects light, the Crab Bot will move back and forth.

void loop() {    
    int leftSensor = analogRead(19);    
    int centerSensor = analogRead(20);    
    int rightSensor = analogRead(21);    

    if(leftSensor < leftBaseLevel)    
    {        
        digitalWrite(11, HIGH); // light the left LEDs        
        digitalWrite(15, HIGH);        
        digitalWrite(12, LOW);        
        digitalWrite(17, LOW);        
        digitalWrite(13, LOW);        
        digitalWrite(18, LOW);    

        SmartInventor.DCMotor(M1, CCW, 50); // move right    
    }    
    else if(rightSensor < rightBaseLevel)    
    {        
        digitalWrite(11, LOW); // light the right LEDs        
        digitalWrite(15, LOW);        
        digitalWrite(12, LOW);        
        digitalWrite(17, LOW);        
        digitalWrite(13, HIGH);        
        digitalWrite(18, HIGH);        
    
        SmartInventor.DCMotor(M1, CW, 50); // move right    
    }
    else if(centerSensor < centerBaseLevel)
    {
        digitalWrite(11, LOW); // light the right LEDs
        digitalWrite(15, LOW);
        digitalWrite(12, LOW);
        digitalWrite(17, LOW);
        digitalWrite(13, HIGH);
        digitalWrite(18, HIGH);

        SmartInventor.DCMotor(M1, CW, 50); // move right
        delay(100);
        SmartInventor.DCMotor(M1, CCW, 50); // move left
        delay(100);

        digitalWrite(11, HIGH); // light the left LEDs
        digitalWrite(15, HIGH);
        digitalWrite(12, LOW);
        digitalWrite(17, LOW);
        digitalWrite(13, LOW);
        digitalWrite(18, LOW);

        SmartInventor.DCMotor(M1, CW, 50); // move right
        delay(100);
        SmartInventor.DCMotor(M1, CCW, 50); // move left
        delay(100);    
    }
}
Step 9

Stop the motors

Finally, add an else statement so the Crab Bot stops if the sensors don’t detect any light.

void loop() {
    int leftSensor = analogRead(19);
    int centerSensor = analogRead(20);
    int rightSensor = analogRead(21);

    if(leftSensor < leftBaseLevel)
    {
        digitalWrite(11, HIGH); // light the left LEDs
        digitalWrite(15, HIGH);
        digitalWrite(12, LOW);
        digitalWrite(17, LOW);
        digitalWrite(13, LOW);
        digitalWrite(18, LOW);

    SmartInventor.DCMotor(M1, CCW, 50); // move right
    }    

    else if(rightSensor < rightBaseLevel)
    {
        digitalWrite(11, LOW); // light the right LEDs
        digitalWrite(15, LOW);
        digitalWrite(12, LOW);
        digitalWrite(17, LOW);
        digitalWrite(13, HIGH);
        digitalWrite(18, HIGH);

        SmartInventor.DCMotor(M1, CW, 50); // move right
    }

    else if(centerSensor < centerBaseLevel)
    {
        digitalWrite(11, LOW); // light the right LEDs
        digitalWrite(15, LOW);
        digitalWrite(12, LOW);
        digitalWrite(17, LOW);
        digitalWrite(13, HIGH);
        digitalWrite(18, HIGH);

        SmartInventor.DCMotor(M1, CW, 50); // move right
        delay(100);
        SmartInventor.DCMotor(M1, CCW, 50); // move left
        delay(100);

        digitalWrite(11, HIGH); // light the left LEDs
        digitalWrite(15, HIGH);
        digitalWrite(12, LOW);
        digitalWrite(17, LOW);
        digitalWrite(13, LOW);
        digitalWrite(18, LOW);

        SmartInventor.DCMotor(M1, CW, 50); // move right
        delay(100);
        SmartInventor.DCMotor(M1, CCW, 50); // move left
        delay(100);
    }
    else
    {
        digitalWrite(11, LOW); // light the middle LEDs
        digitalWrite(15, LOW);
        digitalWrite(12, HIGH);
        digitalWrite(17, HIGH);
        digitalWrite(13, LOW);
        digitalWrite(18, LOW);
    
        SmartInventor.DCMotor(M1, LOOSE, 0); // stop
    }
}
Step 10

Final code

Your final code should look something like this:

#include <SmartInventor.h>

int leftBaseLevel;
int centerBaseLevel;
int rightBaseLevel; 

void setup() {    
    SmartInventor.DCMotorUse();        

    leftBaseLevel = analogRead(19) - 50;    
    centerBaseLevel = analogRead(20) - 50;    
    rightBaseLevel = analogRead(21) - 50;
}

void loop() {    
    int leftSensor = analogRead(19);    
    int centerSensor = analogRead(20);    
    int rightSensor = analogRead(21);    

    if(leftSensor < leftBaseLevel)    
    {        
        digitalWrite(11, HIGH); // light the left LEDs        
        digitalWrite(15, HIGH);        
        digitalWrite(12, LOW);        
        digitalWrite(17, LOW);        
        digitalWrite(13, LOW);        
        digitalWrite(18, LOW);        

        SmartInventor.DCMotor(M1, CCW, 50); // move right    
    }        
    else if(rightSensor < rightBaseLevel)    
    {        
        digitalWrite(11, LOW); // light the right LEDs        
        digitalWrite(15, LOW);        
        digitalWrite(12, LOW);        
        digitalWrite(17, LOW);        
        digitalWrite(13, HIGH);        
        digitalWrite(18, HIGH);        

        SmartInventor.DCMotor(M1, CW, 50); // move right    
    }    
    else if(centerSensor < centerBaseLevel)    
    {           
        digitalWrite(11, LOW); // light the right LEDs        
        digitalWrite(15, LOW);           
        digitalWrite(12, LOW);        
        digitalWrite(17, LOW);        
        digitalWrite(13, HIGH);        
        digitalWrite(18, HIGH);        

        SmartInventor.DCMotor(M1, CW, 50); // move right        
        delay(100);        
        SmartInventor.DCMotor(M1, CCW, 50); // move left        
        delay(100);        

        digitalWrite(11, HIGH); // light the left LEDs        
        digitalWrite(15, HIGH);        
        digitalWrite(12, LOW);        
        digitalWrite(17, LOW);        
        digitalWrite(13, LOW);        
        digitalWrite(18, LOW);        

        SmartInventor.DCMotor(M1, CW, 50); // move right        
        delay(100);            
        SmartInventor.DCMotor(M1, CCW, 50); // move left        
        delay(100);    
    }    
    else    
    {        
        digitalWrite(11, LOW); // light the middle LEDs
        digitalWrite(15, LOW);
        digitalWrite(12, HIGH);
        digitalWrite(17, HIGH);
        digitalWrite(13, LOW);
        digitalWrite(18, LOW);            

        SmartInventor.DCMotor(M1, LOOSE, 0); // stop    
    }
}
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