1) What the TCRT5000 sensor does

The TCRT5000 is a reflective infrared optical sensor. It emits infrared light downward and measures how much light is reflected back from a nearby surface.

• Light surfaces reflect more IR
• Dark surfaces absorb more IR
• The sensor converts this difference into an electrical signal

This contrast-based detection makes the module ideal for:

• Line-following robots (black line on white surface)
• Edge or cliff detection
• Short-range object presence detection

2) Reflective IR sensing principle

The sensor contains:

• An IR LED emitter (usually ~940 nm)
• A phototransistor receiver

When the IR LED emits light:

• White/light surfaces reflect IR strongly
• Black/dark surfaces reflect IR weakly

3) Module overview and internal circuitry

The TCRT5000 module typically includes:

• TCRT5000 reflective IR sensor
• Current-limiting resistor for IR LED
• LM393 comparator (on digital-output variants)
• Potentiometer for threshold adjustment
• Indicator LED

4) Pinout and electrical characteristics

• Logic compatible with 3.3V and 5V MCUs
• DO typically goes LOW when reflection is high (line detected)

5) Analog vs digital output behavior

Analog Output (AO):

• Voltage proportional to reflected IR
• Higher value = more reflection
• Used for fine-grained control and calibration

Digital Output (DO):

• Comparator-based ON/OFF signal
• Threshold set by onboard potentiometer
• Ideal for simple line detection

6) Detection distance and surface effects

• Typical working distance: ~2 mm – 15 mm
• Best contrast at 5–10 mm
• Surface texture and gloss strongly affect readings

7) Wiring to Arduino

TCRT5000 VCC ? Arduino 5V
TCRT5000 GND ? Arduino GND
TCRT5000 AO  ? Arduino A0
TCRT5000 DO  ? Arduino D2
    

8) Arduino Example 1: Analog reflectivity reading

/*
  TCRT5000 Analog Read
  Product #251
*/

const int IR_AO = A0;

void setup() {
  Serial.begin(9600);
}

void loop() {
  int value = analogRead(IR_AO); // 0–1023
  Serial.print("Reflectivity: ");
  Serial.println(value);
  delay(200);
}
    

9) Arduino Example 2: Digital line detection

/*
  TCRT5000 Digital Detection
*/

const int IR_DO = 2;

void setup() {
  pinMode(IR_DO, INPUT);
  Serial.begin(9600);
}

void loop() {
  if (digitalRead(IR_DO) == LOW) {
    Serial.println("Line detected");
  } else {
    Serial.println("No line");
  }
  delay(200);
}
    

10) Arduino Example 3: Simple line-following logic

/*
  Simple Line Logic (single sensor)
*/

const int IR_DO = 2;

void setup() {
  pinMode(IR_DO, INPUT);
}

void loop() {
  bool onLine = (digitalRead(IR_DO) == LOW);

  if (onLine) {
    // move forward
  } else {
    // adjust direction
  }
}
    

11) Threshold adjustment and calibration

• Place sensor over target surface
• Turn potentiometer until LED switches cleanly
• Calibrate under actual lighting conditions
• Re-calibrate if sensor height changes

12) Mechanical placement guidelines

• Mount perpendicular to surface
• Avoid IR LED shadowing the receiver
• Shield from strong sunlight if possible
• Use rigid mounting to avoid vibration

13) Troubleshooting

Always detecting line

• Threshold set too low
• Sensor too close to surface
• Highly reflective background

Never detecting line

• Threshold set too high
• Sensor too far from surface
• Insufficient contrast

14) Quick checklist

TCRT5000 Line Tracking Sensor (#251) Checklist
---------------------------------------------
? Power with 3.3V or 5V
? Maintain consistent sensor height (5–10 mm ideal)
? Use AO for calibration, DO for simple logic
? Adjust threshold under real lighting
? Expect reflectivity, not color detection
? Shield from sunlight for outdoor use
? Rigidly mount sensor to avoid vibration