Skip to main content

Lesson 7.3: Mapping Digital and Analog Sensors into Java Objects

Technical Context​

Sensors are mapped to different hardware buses — Digital, Analog, or I2C. Mapping a DigitalChannel (like a touch sensor) using the AnalogInput class, or vice versa, will result in incorrect voltage readings or hardware errors. The SDK uses distinct classes for each sensor type to enforce this separation and prevent silent logic failures.

How Sensor Mapping Stays Organized​

The SDK differentiates between two common sensor categories:

Digital sensors (e.g., REV Touch Sensor, magnetic limit switches) operate on a binary signal — the pin is either HIGH or LOW. They are instantiated with the DigitalChannel class and return a boolean via getState(). One critical step: you must explicitly call setMode(DigitalChannel.Mode.INPUT) to configure the pin to receive data rather than send it.

Analog sensors (e.g., potentiometers, analog distance sensors) return a continuous voltage between 0V and the maximum port voltage. They are instantiated with the AnalogInput class and return a double via getVoltage(). Analog input ports do not require a mode to be set.

Annotated Code​

package org.firstinspires.ftc.teamcode;

import com.qualcomm.robotcore.eventloop.opmode.OpMode;
import com.qualcomm.robotcore.eventloop.opmode.TeleOp;
import com.qualcomm.robotcore.hardware.DigitalChannel;
import com.qualcomm.robotcore.hardware.AnalogInput;

@TeleOp(name="Sensor_Mapping_Demo")
public class SensorMappingDemo extends OpMode {

    private DigitalChannel touch;
    private AnalogInput    pot;

    @Override
    public void init() {
        // Mapping to a Digital port — requires INPUT mode to be set
        touch = hardwareMap.get(DigitalChannel.class, "limit_switch");
        touch.setMode(DigitalChannel.Mode.INPUT);

        // Mapping to an Analog port — functional immediately upon registration
        pot = hardwareMap.get(AnalogInput.class, "arm_pot");

        telemetry.addData("Status", "Sensors mapped");
    }

    @Override
    public void loop() {
        boolean isPressed  = !touch.getState(); // Active-low: false = pressed
        double  armVoltage = pot.getVoltage();

        telemetry.addData("Limit Switch Pressed", isPressed);
        telemetry.addData("Arm Pot Voltage",      armVoltage);
    }
}

Fill-in-the-Blank Practice​

  1. A touch sensor is mapped using the __________ class in the SDK.
  2. To configure a digital sensor port to receive data, you must set its mode to DigitalChannel.Mode.__________.
  3. A potentiometer is instantiated using the __________ class, and its value is read with getVoltage().
Show answers
  1. DigitalChannel
  2. INPUT
  3. AnalogInput

Template Challenge​

Robot Scenario: You are adding a "claw_sensor" (Digital) and a "height_pot" (Analog) to your robot. Map these components and set the required mode for the digital sensor, then display both readings on the Driver Station.

package org.firstinspires.ftc.teamcode;

import com.qualcomm.robotcore.eventloop.opmode.OpMode;
import com.qualcomm.robotcore.eventloop.opmode.TeleOp;
import com.qualcomm.robotcore.hardware.DigitalChannel;
import com.qualcomm.robotcore.hardware.AnalogInput;

@TeleOp(name="Sensor_Map_Challenge")
public class SensorMap extends OpMode {

    private DigitalChannel clawSensor;
    private AnalogInput    heightPot;

    @Override
    public void init() {
        // INSERT CODE HERE: Map the DigitalChannel named "claw_sensor"
        // INSERT CODE HERE: Set its mode to INPUT

        // INSERT CODE HERE: Map the AnalogInput named "height_pot"
    }

    @Override
    public void loop() {
        telemetry.addData("Claw Sensor State", clawSensor.getState());
        telemetry.addData("Height Voltage",    heightPot.getVoltage());
    }
}
Show answer
@Override
public void init() {
    clawSensor = hardwareMap.get(DigitalChannel.class, "claw_sensor");
    clawSensor.setMode(DigitalChannel.Mode.INPUT);

    heightPot = hardwareMap.get(AnalogInput.class, "height_pot");

    telemetry.addData("Status", "Sensors mapped");
}

Ready to move on?

Sign in with Google to save your progress with Telemark, or continue without saving.