TCS3200 Programmable Color Light-to-Frequency Sensor

Working Principle

The TCS3200 (and earlier TCS230) is a programmable color light-to-frequency converter. It contains an 8×8 array of photodiodes with four types of filters: 16 red, 16 green, 16 blue, and 16 clear (no filter). Two select pins (S2, S3) choose which filter group is active. The current from selected photodiodes drives a current-to-frequency converter, outputting a square wave whose frequency is proportional to light intensity of the selected colour channel.

Analogy: Imagine looking through coloured glasses — red glasses block everything except red light. The TCS3200 has three pairs of glasses and counts how many photons get through each.

Electrical Characteristics

Parameter	Value
Supply Voltage	2.7 V – 5.5 V
Output	Square wave (frequency proportional to intensity)
Colour Channels	Red, Green, Blue, Clear
Photodiode Array	8 × 8 (64 photodiodes)
Frequency Scaling	2%, 20%, 100% (selectable via S0, S1)
Non-linearity	0.2% at 50 kHz
Dark Frequency	12 Hz typical
Package	SOIC-8 (chip) or GY-31 module (with LEDs)

Interfacing with an MCU

The TCS3200 module (GY-31) has pins: VCC, GND, S0, S1 (frequency scaling), S2, S3 (filter selection), OUT (frequency), and OE (output enable, usually tied LOW). Four white LEDs illuminate the target object.

Calibration

Colour accuracy depends on white-balance calibration:

• White reference: Place a white card at the sensor distance; read R, G, B frequencies. These represent maximum reflectance per channel.
• Black reference: Block all light; read R, G, B to determine the noise floor.
• Mapping: R_mapped = map(R_raw, R_black, R_white, 0, 255) — repeat for G and B.
• Consistent lighting: The on-board LEDs provide fixed illumination; ambient light introduces error — shade the sensor.

Code Example

/*
 * TCS3200 Color Sensor — Arduino
 * Wiring: S0→4, S1→5, S2→6, S3→7, OUT→8
 */
#define S0 4
#define S1 5
#define S2 6
#define S3 7
#define OUT_PIN 8

void setup() {
    Serial.begin(9600);
    pinMode(S0, OUTPUT); pinMode(S1, OUTPUT);
    pinMode(S2, OUTPUT); pinMode(S3, OUTPUT);
    pinMode(OUT_PIN, INPUT);

    /* Frequency scaling to 20% */
    digitalWrite(S0, HIGH); digitalWrite(S1, LOW);
    Serial.println("TCS3200 Color Sensor Ready");
}

int readColor(bool s2, bool s3) {
    digitalWrite(S2, s2); digitalWrite(S3, s3);
    delay(20);
    return pulseIn(OUT_PIN, LOW);  /* Period ∝ 1/frequency */
}

void loop() {
    int red   = readColor(LOW, LOW);
    int green = readColor(HIGH, HIGH);
    int blue  = readColor(LOW, HIGH);

    Serial.print("R: "); Serial.print(red);
    Serial.print(" G: "); Serial.print(green);
    Serial.print(" B: "); Serial.println(blue);

    /* Simple colour classifier */
    if (red < green && red < blue) Serial.println("  → RED");
    else if (green < red && green < blue) Serial.println("  → GREEN");
    else if (blue < red && blue < green) Serial.println("  → BLUE");
    else Serial.println("  → UNCLEAR");

    delay(500);
}

Real-World Applications

Limitations

• Ambient light sensitivity: External light sources shift readings — enclose the sensor and object in a light-proof chamber.
• No true spectroscopy: Reports broad R/G/B bands, not narrow wavelengths — cannot distinguish metameric colours.
• Distance dependent: Reading changes with target distance; maintain a fixed sensor-to-object gap.
• Glossy surfaces: Specular reflections from shiny objects skew colour readings — matte targets are ideal.