ROBOTC: Using the NXT 2.0 Colour Sensor as a Light Sensor

Using the NXT 2.0 Colour Sensor as an old fashioned NXT 1.0 Light Sensor as very simple in NXT-G but a little more involved in ROBOTC. The old Light Sensor uses a small red LED to illuminate the target and a small sensor to see how much was reflected. The new colour sensor can be used in a very similar way.  The only thing is you will need to do some work yourself to turn it into a normalised value (0-100).

Below is the code for a simple program that allows you to read both the raw value from the Colour Sensor and a normalised one.  Make sure you change the blackValue and whiteValue variables to match your own environment.

#pragma config(Sensor, S1, COLOUR, sensorCOLORRED)
//*!!Code automatically generated by 'ROBOTC' configuration wizard !!*//

/*
* Program to use the NXT 2.0 colour sensor as a standard Lego Light sensor
* Written by Xander Soldaat 18-Feb-2011
*/

// Calibration values, these may be different for you
const int blackValue = 220;
const int whiteValue = 580;

// Normalise a raw value, returns a value from 0 to 100
int normaliseReading(int rawValue) {
  // Anything less than the black value should return 0
  if (rawValue <= blackValue)
    return 0;
  
  // Anything brighter than the white value should return 100
  else if (rawValue >= whiteValue)
    return 100;
  
  // Anything else should be calculated in a scale from 0-100%
  else
    return ((long)(rawValue - blackValue) * 100) / (whiteValue - blackValue);
}

task main () {
  int rawValue = 0;
  int normalisedValue = 0;
  
  while (true) {
    // Get the raw value from the sensor.
    rawValue = SensorRaw[COLOUR];
    
    // Calculate the normalised value
    normalisedValue = normaliseReading(rawValue);
    
    nxtDisplayTextLine(4, "Raw: %3d", rawValue);
    nxtDisplayTextLine(5, "Norm: %3d", normalisedValue);
    wait1Msec(100);
  }
}

You can download the program here: [LINK].