Programming Touch Sensors

This section applies to the use of the REV Touch Sensor or Limit Switch. Requirements may vary when using other 3rd party touch sensors.

The REV Touch Sensor must be configured to digital port 1, 3, 5, or 7.

Touch Sensor Basics

The following example code's file name is: HelloRobot_TouchSensor

Let's start by breaking down how a touch sensor works at its core!

The information collected by a touch sensor comes in two states, also known as binary states. This information is perfect to use with a conditional statement like an if/else statement.

The line test_touch.isPressed(); collects the binary TRUE/FALSE state from the touch sensor and acts as the condition for the if/else statement.

if (test_touch.isPressed()){
    //Touch Sensor is pressed 
} else {
    //Touch Sensor is not pressed 
        }

The code above highlights the basics structure of the if/elsestatement for a touch sensor. We could read this line of code as "If the touch sensor is pressed do ____, else if the touch sensor is not pressed do _____."

So with this in mind:

• Touch sensor pressed = true

• Touch sensor NOT pressed = false

Adding Telemetry

It's always helpful for us to be able to see what the robot thinks its doing on our Driver Hub's screen. To do this let's request the robot shares some telemetry data while our program is active.

Within our if/else statement we'll add a telemetry.addData for whether the touch sensor is pressed or not.

            if (test_touch.isPressed()){
                //Touch Sensor is pressed.
                telemetry.addData("Touch Sensor", "Is Pressed");
            } else {
                //Touch Sensor is not pressed 
                telemetry.addData("Touch Sensor", "Is Not Pressed");
                        }

How our robot displays this data back to our Driver Hub is up to us to define. In this case we would see something similar to the following when the touch sensor is pressed:

The blue text within our quotation marks controls what will show on the Driver Hub. With that in mind we could have the robot say "Hello World!" when the button is pressed:

To finish our program before testing we need to add a telemetry.update(); after our if/else statement to request our robot updates the telemetry each time it loops:

        // Wait for the game to start (driver presses PLAY)
        waitForStart();
        
        // run until the end of the match (driver presses STOP)
        while (opModeIsActive()) {
        
            if (test_touch.isPressed()){
                //Touch Sensor is pressed.
                telemetry.addData("Touch Sensor", "Is Pressed");
            } else {
                //Touch Sensor is not pressed 
                telemetry.addData("Touch Sensor", "Is Not Pressed");
                        }
        telemetry.update();
}

Touch Sensor as a Limit Switch

At the moment, our robot does not have any senses to help navigate the world around it like you might. However, that's the key advantage to adding sensors to our design.

For the touch sensor, one of the most common uses is for it to act as a limit switch. This will help the robot know when it needs to halt the movement of a mechanism, like an arm or lift, that's at its limit similar to how your nerves help to tell your brain to do the same.

We can test this idea by adding on to our existing if/else statement. This time we are going to ask our motor to move until our sensor is pressed:

 if (test_touch.isPressed()){
    //Touch Sensor is pressed  
     test_motor.setPower(0);
     telemetry.addData("Touch Sensor", "Is Pressed");
    
} else {
    //Touch Sensor is not pressed 
    test_motor.setPower(0.3);
    telemetry.addData("Touch Sensor", "Is Not Pressed");
                        }

Test it out! What happens when you test your program?

You'll learn more about how to use this with a completed arm in Part 2: Robot Control!

Click to view full code!

import com.qualcomm.robotcore.eventloop.opmode.Disabled;
import com.qualcomm.robotcore.hardware.DcMotor;
import com.qualcomm.robotcore.hardware.Servo;
import com.qualcomm.robotcore.hardware.TouchSensor;
import com.qualcomm.robotcore.eventloop.opmode.LinearOpMode;
import com.qualcomm.robotcore.eventloop.opmode.TeleOp;

@TeleOp

public class HelloRobot_TouchSensor extends LinearOpMode {
    TouchSensor test_touch;  // Touch sensor Object
    private DcMotor test_motor = null;
    private Servo test_servo = null;
    
    @Override
public void runOpMode() {
        test_motor = hardwareMap.get(DcMotor.class, "test_motor");
        test_servo = hardwareMap.get(Servo.class, "test_servo");
        test_touch = hardwareMap.get(TouchSensor.class, "test_touch");
        
        // Wait for the game to start (driver presses PLAY)
        waitForStart();
        
        // run until the end of the match (driver presses STOP)
        while (opModeIsActive()) {
        
            if (test_touch.isPressed()){
                //Touch Sensor is pressed.
                test_motor.setPower(0);
                telemetry.addData("Touch Sensor", "Is Pressed");
            } else {
                //Touch Sensor is not pressed 
                test_motor.setPower(0.3);
                telemetry.addData("Touch Sensor", "Is Not Pressed");
                        }
        telemetry.update();
        }
    }
}

Reversing it

In the above example the if/else is checking first for if the touch sensor is pressed. The full statement could be read as "If the touch sensor is pressed set the motor's power to 0 else, if it is not pressed, set the power to 0.3". This statement can be reversed by adding a ! before test_touch.isPressed().

   if (!test_touch.isPressed()){
            //Touch Sensor is not pressed  
           test_motor.setPower(0.3);
           telemetry.addData("Touch Sensor", "Is Not Pressed");
    
          } else {
            //Touch Sensor is pressed 
            test_motor.setPower(0);
            telemetry.addData("Touch Sensor", "Is Pressed");
                        }

In OnBot Java the operator ! tells the code to look for the opposite or to "not" be what is being called. So in this instance our if/else statement is checking if the touch sensor is NOT pressed first.

Give it a try!