How to set up ultrasonic and IR sensors for object detection on a conveyor

thijs · September 2, 2026, 12:14am

Based on contributions by Okay.

Ultrasonic and IR (infrared) distance sensors are commonly used to detect boxes on a conveyor belt, for example to trigger a conveyor stop or tell a robot when to pick up or place an object. This guide covers wiring, basic Arduino code, and testing for both sensor types.

What you need

Ultrasonic sensor (e.g. HC-SR04)
IR sensor (e.g. GP2Y0A21YK0F)
Arduino (or another microcontroller with digital/analog I/O)
Breadboard and wires
5V power supply for both sensors
Boxes of different sizes to test with

Steps

1. Understand the two sensor types

Ultrasonic sensors emit high-frequency sound pulses and measure how long the echo takes to return, converting that time into a distance. They work well for irregularly shaped or transparent objects and are suited to longer-range detection, object counting, or level measurement.

IR sensors emit infrared light and measure the reflection. They respond quickly and are best for opaque, non-reflective surfaces at shorter range — useful for edge detection and more precise positioning.

2. Wire the ultrasonic sensor

VCC → 5V
GND → Ground
Trig pin → a digital pin (e.g. pin 9)
Echo pin → another digital pin (e.g. pin 10)

Double-check the wiring before powering it on.

3. Wire the IR sensor

VCC → 5V
GND → Ground
OUT pin → an analog input pin (e.g. A0)

The IR sensor’s output is analog, so it must be read through an analog input pin.

4. Program the ultrasonic sensor

const int trigPin = 9;
const int echoPin = 10;
long duration;
int distance;

void setup() {
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  Serial.begin(9600);
}

void loop() {
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  duration = pulseIn(echoPin, HIGH);
  distance = duration * 0.034 / 2;  // Speed of sound: ~0.034 cm/µs, divided by 2 for the round trip
  Serial.println(distance);

  delay(1000);  // Wait 1 second before the next reading
}

This sends a pulse, waits for the echo, and prints the calculated distance (in cm) to the Serial Monitor.

5. Program the IR sensor

const int irPin = A0;
int irValue;

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

void loop() {
  irValue = analogRead(irPin);  // Read the raw analog value from the IR sensor
  Serial.println(irValue);
  delay(1000);
}

This prints the raw analog reading, which changes with the distance to the object. Convert it to a distance using your specific sensor’s datasheet curve if you need actual units.

6. Position and test on the conveyor

Mount the sensors where the boxes will pass. Ultrasonic sensors should point perpendicular to the box surface for the most accurate reading; IR sensors should point directly at the object.
Watch the Serial Monitor while boxes pass: for the ultrasonic sensor, check that the measured distance matches the real distance; for the IR sensor, check that the analog value changes consistently as a box gets closer or farther away.
Adjust sensor height/angle if readings are inconsistent or boxes are missed.