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TCS34725

The TCS34725 is a color light-to-digital converter that provides digital readings for red, green, blue (RGB), and clear light sensing values. In a specific application, it was utilized to detect black and blue tiles. The sensor was strategically positioned at the bottom front of the robot, allowing it to have a time buffer for timely responses.

Link

Library

The main methods used were: 

tcs.getRawData(&red_r, &green_r, &blue_r, &clear_r);
tcs.getRGB(&red, &green, &blue);

Processing RGB input

The idea behind our implementation to relate a RGB output with a color was very simple:

  • For each color, establish the expected values for each color channel.

// BLUE TILE
  static constexpr float kRedValueInBlue_ = 211;
  static constexpr float kGreenValueInBlue_ = 770;
  static constexpr float kBlueValueInBlue_ = 1190;
  // BLACK TILE
  static constexpr float kRedValueInBlack_ = 70.00;
  static constexpr float kGreenValueInBlack_ = 90.00;
  static constexpr float kBlueValueInBlack_ = 90.00;
- COLOR SENSOR CALIBRATION: Calibration is performed using calibrateTCS(), place the robot directly under each color on the field and read the values printed to Serial.

  • Update the constants to match the displayed readings.

If readings look off, adjust integration time and gain in TCS.h(): - Undersaturated (values too small / differences barely distinguishable): increase integration time or gain. - Oversaturated (values maxed out / clipping): decrease integration time or gain.

Recalibrate whenever the arena lighting or sensor mounting height changes.

  • Each expected value passes through a treshold that makes a range of values for color.
  static constexpr uint8_t rgbThreshold = 200; // Makes range: baseValue +/- 200

  • After each reading, check if the values are within the expected range for each color.

  • Return a value indicating a specific color if all three channels match the expected range.

char TCS::getColor() {
  updateRGBC(); // Update the RGB values
  char colorLetter = kUndefinedColor_;

  if (red_ > kMinRedValueInBlue_ && green_ > kMinGreenValueInBlue_ &&
      blue_ > kMinBlueValueInBlue_ && red_ < kMaxRedValueInBlue_ &&
      green_ < kMaxGreenValueInBlue_ && blue_ < kMaxBlueValueInBlue_) {
    colorLetter = kBlueColor_;
#if DEBUG_TCS
    Serial.println("blue");
#endif
  } else if (red_ > kMinRedValueInBlack_ && green_ > kMinGreenValueInBlack_ &&
             blue_ > kMinBlueValueInBlack_ && red_ < kMaxRedValueInBlack_ &&
             green_ < kMaxGreenValueInBlack_ && blue_ < kMaxBlueValueInBlack_) {
    colorLetter = kBlackColor_;
#if DEBUG_TCS
    Serial.println("black");
#endif
  } else if (red_ > kMinRedValueInCheckpoint_ &&
             green_ > kMinGreenValueInCheckpoint_ &&
             blue_ > kMinBlueValueInCheckpoint_ &&
             red_ < kMaxRedValueInCheckpoint_ &&
             green_ < kMaxGreenValueInCheckpoint_ &&
             blue_ < kMaxBlueValueInCheckpoint_) {
    colorLetter = kCheckpointColor_;
#if DEBUG_TCS
    Serial.println("checkpoint");
#endif
  } else {
    colorLetter = kUndefinedColor_;
#if DEBUG_TCS
    Serial.println("unknown");
#endif
  }

#if DEBUG_TCS
  Serial.print("colorLetter: ");
  Serial.println(colorLetter);
#endif
  return colorLetter;
}