TCRT5000 Reflective IR Optical Sensor

Working Principle

The Vishay TCRT5000 is a reflective optical sensor containing an IR LED emitter and a phototransistor detector in one package. The LED emits 950 nm infrared light. When a reflective surface is within range (1–25 mm), light bounces back to the phototransistor, causing it to conduct current proportional to the reflected intensity.

Analogy: Imagine holding a flashlight and a light-meter side by side, pointing at a wall. The closer and whiter the wall, the more light bounces back to your meter. Dark surfaces absorb the light, giving low readings.

Electrical Characteristics

Parameter	Value
Emitter Wavelength	950 nm (infrared)
Optimal Detection Distance	2.5 mm (peak sensitivity)
Working Range	1 – 25 mm
Emitter Forward Current	60 mA max (20 mA typical)
Collector Current (detector)	Up to 100 mA
Output	Analog (phototransistor collector) or digital via comparator module
Package	Through-hole, 4-pin

Interfacing with an MCU

The bare TCRT5000 has 4 pins: emitter anode, emitter cathode, collector, and emitter (phototransistor). Most hobbyists use breakout modules with built-in comparator (LM393) providing both analog (A0) and digital (D0, adjustable threshold via pot) outputs.

Calibration

Calibration depends on target surface and distance:

• Distance tuning: Mount the sensor 2–5 mm above the surface for line-following; adjust if the analog reading saturates or is too low.
• Threshold adjustment: On modules with an LM393, turn the potentiometer until the digital output toggles at the desired reflectance boundary (e.g., black vs white tape).
• Multi-sensor normalisation: Read each sensor on a known white and black surface; map raw ADC values to a 0–1000 normalised range.

Code Example

/*
 * TCRT5000 Line Follower — Arduino
 * Uses breakout module with A0 (analog) and D0 (digital)
 * Wiring: VCC→5V, GND→GND, A0→A0, D0→Pin2
 */
#define ANALOG_PIN  A0
#define DIGITAL_PIN 2

void setup() {
    Serial.begin(9600);
    pinMode(DIGITAL_PIN, INPUT);
    Serial.println("TCRT5000 Ready");
}

void loop() {
    int analogVal = analogRead(ANALOG_PIN);  /* 0-1023 */
    int detected  = digitalRead(DIGITAL_PIN);

    Serial.print("Analog: "); Serial.print(analogVal);
    Serial.print(" | Object detected: ");
    Serial.println(detected == LOW ? "YES (reflective)" : "NO (dark/absent)");

    delay(200);
}

Real-World Applications

Limitations

• Short range: Effective only to ~25 mm — unsuitable for object detection beyond close proximity.
• Ambient IR: Direct sunlight contains strong IR that can swamp the phototransistor, causing false readings outdoors.
• Surface dependent: Works best on matte surfaces; glossy or transparent materials cause specular reflections or pass-through.
• Analogue noise: The bare sensor output varies with temperature and LED ageing; periodic recalibration is recommended.