Reading sensors

Choose the measurement#

References: VEX Robotics: Inertial Sensor — C++ API (opens in a new tab) · VEX Robotics: Rotation Sensor — C++ API (opens in a new tab) · VEX Robotics: Distance Sensor — C++ API (opens in a new tab) · VEX Robotics: Optical Sensor — C++ API (opens in a new tab)

Read an optical sensor#

The Optical Sensor can report proximity and a hue angle around the color wheel. Check isNearObject() before classifying color. A hue value without an object in the intended sensing area is not a reliable detection.

The example checks a red interval that crosses 0° using an OR condition. Set the light power and test your own thresholds with the real object, mounting distance, and expected ambient lighting.

optical colorSensor(PORT9);

bool isRedObject() {
  if (!colorSensor.isNearObject()) return false;
  double hue = colorSensor.hue();
  return hue >= 340.0 || hue <= 20.0;
}

void autonomous() {
  stopDrive();
  colorSensor.setLightPower(50, percent);
  timer elapsed;
  elapsed.reset();
  while (elapsed.time(msec) < 10000) {
    Brain.Screen.setCursor(1, 1);
    Brain.Screen.print("near %d hue %.1f red %d   ",
      colorSensor.isNearObject(), colorSensor.hue(), isRedObject());
    wait(50, msec);
  }
  colorSensor.setLight(ledState::off);
}

References: VEX Robotics: Optical Sensor — C++ API (opens in a new tab) · VEX Robotics: Brain Screen — C++ API (opens in a new tab)

Reject invalid readings#

Check that the expected device is connected, that an object is detected when required, and that the value is finite and inside a plausible range. A missing reading should trigger a defined fallback instead of being treated as a real distance.

Keep the original units until a clear conversion point. For example, convert millimeters to inches with rangeMm / 25.4 before combining a distance reading with an inch-based pose.

References: VEX Robotics: Distance Sensor — C++ API (opens in a new tab)

Filter noise without hiding motion#

A median over a few recent valid readings can reject an isolated spike. An average can smooth noise but also delays the signal. That delay matters when a moving object passes a color sensor or a robot approaches a wall.

For a detection, require several consecutive matching samples if brief flicker is a problem. Reset the counter when the condition fails. Confirm that the added delay still leaves enough time to respond. A stable incorrect object can pass a filter, so filtering does not establish object identity.

Test before controlling a motor#

1. Print the raw reading while the robot is stationary.
2. Move one object or shaft at a time. Confirm the sign, units, wraparound, and useful range.
3. Try no object, an unexpected surface, and normal room lighting changes.
4. Record observed ranges before selecting a threshold.
5. Only connect the reading to motor control once you can explain both the normal and invalid states.