Building an Infrared Distance Sensor

Measure distance with light. A Sharp infrared sensor bounces a beam off an object and reports, as a voltage, the angle it returns at — closer objects give a higher reading. The Arduino turns that into an approximate distance and lights an LED when something comes near: a touchless switch, a hand-wave trigger, or a robot's eyes. Unlike the ultrasonic sensor, this uses infrared light, works at short range, and makes no sound.

中级

1 hour

说明

Wire the sensor and LED

The Sharp sensor has a 3-wire cable: VCC (red) to Arduino 5V, GND (black) to GND, and signal (white or yellow) to A0. On the breadboard, wire an LED from pin 7 through a 330 Ω resistor to GND (long leg to the pin).

此步骤所需材料：

Arduino Uno R31 个

Infrared Proximity Sensor - Sharp GP2Y0A21YK1 个

LED - Basic 5mm1 个

Resistor 330 Ohm 1/6 Watt PTH - 20 pack1 包

Breadboard1 个

Jumper Wires (Male-to-Male)1 包

Connect and open the IDE

Plug the Arduino into your computer with the USB cable, open the Arduino IDE, and select Arduino Uno and its serial port.

此步骤所需材料：

USB-B Cable1 个

所需工具：

Computer with Arduino IDE

Upload the distance sketch

Paste this sketch and upload, then open the Serial Monitor. It reads the sensor, estimates the distance, and lights the LED when something is within 20 cm.

ir_distance_sensor.inoarduino

// Sharp GP2Y0A21YK infrared distance sensor (valid ~10-80 cm).
// The output is NON-LINEAR (roughly 1/distance); the formula below is a common
// approximation - calibrate against known distances if you need accuracy.
// Sensor signal on A0; indicator LED on pin 7.

const int IR_PIN = A0;
const int LED_PIN = 7;
const int NEAR_CM = 20;   // light the LED when something is closer than this

void setup() {
  pinMode(LED_PIN, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  int raw = analogRead(IR_PIN);
  float volts = raw * (5.0 / 1023.0);

  // approximate distance in cm for the GP2Y0A21 curve
  float distance = 27.86 * pow(volts, -1.15);

  Serial.print(distance);
  Serial.println(" cm");

  if (distance < NEAR_CM) {
    digitalWrite(LED_PIN, HIGH);   // object nearby
  } else {
    digitalWrite(LED_PIN, LOW);
  }
  delay(200);
}

Test and understand the curve

Open the Serial Monitor and move your hand between about 10 and 80 cm — the printed distance should track it, and the LED lights inside 20 cm. Two things to know: below ~10 cm the reading becomes ambiguous (the sensor's curve folds back), and the output is non-linear, so for real accuracy note the raw value at a few known distances and fit your own curve.

Put it to work

Use it as a touchless switch (wave to trigger), a shelf or drawer 'is-it-open' sensor, or an obstacle detector for a small robot. Change NEAR_CM to set the trigger distance, or swap in the short-range (4–30 cm) or long-range (20–150 cm) Sharp sensor for a different span.