Touch Sensor Guide

The touch sensor is a simple digital switch. It returns a boolean value: either pressed or not pressed.

[!NOTE] Even though it’s called a “Touch” sensor, it behaves exactly like a limit switch or a button. In code, it’s a DigitalChannel that returns true or false.

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To use a touch sensor as a digital input, use the DigitalChannel class.

import com.qualcomm.robotcore.hardware.DigitalChannel;

DigitalChannel touchSensor = hardwareMap.get(DigitalChannel.class, "touchSensor");
// Important: Set the mode to INPUT
touchSensor.setMode(DigitalChannel.Mode.INPUT);

The getState() method returns the current electrical state. For most FTC sensors (like the REV Touch Sensor), false means the sensor is pressed (grounded), and true means it is open.

if (touchSensor.getState() == false) {
    telemetry.addData("Touch", "IS PRESSED");
} else {
    telemetry.addData("Touch", "Not Pressed");
}

Tip

Use !touchSensor.getState() to get a “logic high” when the button is pressed.

If you have a lift or an arm, you can place a touch sensor at the extreme end of its range. When the mechanism hits the sensor, you can:

1. Stop the motor immediately to prevent damage.
2. Reset the encoder to zero to ensure your software stays calibrated.

if (limitSwitch.getState() == false) {
    // Stop and reset encoder once it hits the bottom
    slideMotor.setMode(DcMotor.RunMode.STOP_AND_RESET_ENCODER);
    slideMotor.setMode(DcMotor.RunMode.RUN_USING_ENCODER);
}

4. Single-Press Logic (Debouncing)

If you want to toggle something (like a claw) when you press a touch sensor, you need to make sure it only triggers once per press.

boolean lastState = false;
boolean clawOpen = false;

// Inside your loop:
boolean currentState = touchSensor.isPressed();
if (currentState && !lastState) {
    // This only runs the moment the sensor is FIRST pressed
    clawOpen = !clawOpen; 
}
lastState = currentState;

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This example shows how to use a DigitalChannel as a limit switch for a simple motor-based lift.

package org.firstinspires.ftc.teamcode;

import com.qualcomm.robotcore.eventloop.opmode.LinearOpMode;
import com.qualcomm.robotcore.eventloop.opmode.TeleOp;
import com.qualcomm.robotcore.hardware.DigitalChannel;
import com.qualcomm.robotcore.hardware.DcMotor;

@TeleOp(name = "Digital Limit Switch Example", group = "Sensor")
public class TouchSensorExample extends LinearOpMode {

    private DigitalChannel limitSwitch;
    private DcMotor liftMotor;

    @Override
    public void runOpMode() {
        // 1. Initialize hardware
        limitSwitch = hardwareMap.get(DigitalChannel.class, "touchSensor");
        limitSwitch.setMode(DigitalChannel.Mode.INPUT);
        
        liftMotor = hardwareMap.get(DcMotor.class, "liftMotor");

        telemetry.addData("Status", "Initialized");
        telemetry.update();

        waitForStart();

        while (opModeIsActive()) {
            // 2. Control Motor with joystick
            double liftPower = -gamepad1.left_stick_y;

            // 3. Limit Switch Logic:
            // State is 'false' when the sensor is pressed
            boolean isPressed = !limitSwitch.getState(); 

            if (isPressed && liftPower < 0) {
                 liftMotor.setPower(0);
                 liftMotor.setMode(DcMotor.RunMode.STOP_AND_RESET_ENCODER);
                 liftMotor.setMode(DcMotor.RunMode.RUN_USING_ENCODER);
                 telemetry.addData("Limit", "LIFT AT BOTTOM");
            } else {
                 liftMotor.setPower(liftPower);
                 telemetry.addData("Limit", "Normal Operation");
            }

            // 4. Telemetry output
            telemetry.addData("Lift Power", "%.2f", liftPower);
            telemetry.addData("Switch Pressed", isPressed);
            telemetry.update();
        }
    }
}

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