D-1 Test Mechanical Bumpers

First, you'll code an app to test your mechanical bumpers.

Be sure that you've first checked the positions of your wire whiskers and bumper boards to make any necessary physical adjustments. (If necessary, refer back to the introduction for this tutorial.)

Save Copy of App With New Name

In your Arduino code editor, open your existing app named pivot_angle_test. Use the "Save As" command to save a copy as a different app named: mechanical_bumper_test

Once you saved the new app name, modify the block comment near the beginning of the app code to change Pivot Angle Test to Mechanical Bumper Test.

Create Objects for Bumpers

The SparkFun RedBot Library also defines a class named RedBotBumper that is used to control the left and right mechanical bumpers.

You'll need to create two new RedBotMotors objects for your left and right mechanical bumpers as part of the global variables in your app. Add this code before the setup() function:

RedBotBumper leftBumper(3);
RedBotBumper rightBumper(11);

Hopefully, the code syntax for creating new objects is starting to look familiar:

  • RedBotBumper declares the class for the new object.

  • leftBumper and rightBumper represent unique names for each object. Again, you decide what to name your objects. They should make sense to anyone reading the code.

  • 3 and 11 represent the I/O pin numbers that the left and right bumpers should be connected to. If your bumpers were connected to different pins, you'd change these pin numbers.

Add Custom Function to Check Bumpers

You'll add another custom function named checkBumpers() which will contain code to check whether the left or right mechanical bumpers have collided with an obstacle.

The RedBotBumper class defines a method named read() which is used to detect whether or not a bumper has collided with an obstacle. Each bumper acts like a switch or button.

The read() method will return a value of either HIGH or LOW:

  • If the value is LOW, it means the bumper has collided with an obstacle (i.e., the wire whisker has bent backwards far enough to make electrical contact with the metal screw on the bumper board).

Add this custom function after the loop() function (i.e., after its closing curly brace):

void checkBumpers() {
  if (leftBumper.read() == LOW) {
    // add code if left whisker collides: brake, back up, turn right
    motors.brake();
    tone(speaker, 1000, 200);
    
  }
  else if (rightBumper.read() == LOW) {
    // add code if right whisker collides: brake, back up, turn left
    motors.brake();
    tone(speaker, 1000, 200);
    
  }
}

You can see that the custom function contains an if-else statement to check the left and right bumpers. If a collision is detected, the first response is to brake the motors (which hopefully makes sense). It will also use the speaker to produce an "alert" sound.

You'll also notice that this function uses an alternate form of the tone() method, which saves a bit of coding. Notice that three parameters (instead of just two) are listed inside the parentheses:

  • speaker represents the speaker's pin number (which was declared as a global variable)

  • 250 represents the frequency of the tone (which can be any value between 20-20000)

  • 200 represents the duration (in milliseconds) to play the tone. After the duration is over, the tone will automatically stop playing.

By including a third parameter for the duration of the tone, you don't have to include the delay() and noTone() code statements, which is convenient.

Later, you'll add other code within the function to make the robot perform additional actions (such as backing up, etc.) when a collision is detected.

KEEP OTHER CUSTOM FUNCTIONS: Be sure to keep the driveDistance() and pivotAngle() custom functions in your app code. You'll use these custom functions when you modify this app in the next step.

Call Custom Function in Loop

You'll need to call the checkBumpers() function within the loop() function.

However, you first need to delete all the existing code within the loop() function (including the "Press to Start" code that checks if the button is pressed).

Then add a code statement to call the checkBumpers() function within the loop() function.

For reference, your loop() function should now look like this:

void loop() {
  // put your main code here, to run repeatedly:
  checkBumpers();  
}

Upload App to Robot

Follow the steps to connect your robot to your computer, and upload the app.

For this app, you don't have to unplug the USB cable. You can also just keep the robot standing upright on its back end (with its wheels in the air).

Use your finger to press down on the wire whisker of the left bumper. When the wire has bent far enough to touch the metal screw on the bumper board, you should hear a tone. If you release the whisker, the tone should stop. Repeat this test for the right bumper.

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