IR obstacle sensor with ESP32 DevKit V1 — 3.3 V wiring and counter

The IR obstacle module bounces infrared off anything in front of it and gives a clean digital LOW when something is within range. It is used in line-following and obstacle-avoiding robots, hand-wave switches and simple object counters.

On the ESP32 DevKit V1 the key point is the supply: the module’s output follows VCC, so running it from 3V3 keeps the signal at a safe level with no divider. The sketch counts each object that breaks the beam.

Wiring

Board quirks

• Power it from 3V3, not VIN. The comparator output is pulled up to VCC, so at 5 V it would put 5 V on the GPIO. The module works fine at 3.3 V, with a slightly shorter range.
• Set the range with the blue potentiometer while watching the green LED, not the serial output. Typical range is 2–15 cm, less on black or shiny surfaces.
• Sunlight and halogen lamps contain lots of infrared and can trigger it constantly — shade the sensor for outdoor or window-side use.
• GPIO18 is a plain GPIO (also VSPI SCK). If your project uses SPI, D27, D32 or D33 work just as well; avoid D2, D12 and D15 because the module holds OUT at a fixed level during reset.

Code

// IR obstacle sensor module (FC-51 style) on an ESP32 DevKit V1.
// VCC → 3V3, GND → GND, OUT → D18 (GPIO18). OUT goes LOW when an obstacle is in range.

constexpr uint8_t OBSTACLE_PIN = 18;

bool lastBlocked = false;
uint32_t count = 0;

void setup() {
  Serial.begin(115200);
  pinMode(OBSTACLE_PIN, INPUT);  // the module has its own pull-up to VCC (3.3 V here)
  Serial.println("IR obstacle sensor on GPIO18 — wave a hand in front of it");
}

void loop() {
  bool blocked = digitalRead(OBSTACLE_PIN) == LOW;
  if (blocked && !lastBlocked) {
    count++;
    Serial.printf("Obstacle detected (#%lu)\n", (unsigned long)count);
  } else if (!blocked && lastBlocked) {
    Serial.println("Path clear");
  }
  lastBlocked = blocked;
  delay(10);
}

// IR obstacle sensor module (FC-51 style) on an ESP32 DevKit V1.
// VCC → 3V3, GND → GND, OUT → D18 (GPIO18). OUT goes LOW when an obstacle is in range.

constexpr uint8_t OBSTACLE_PIN = 18;

bool lastBlocked = false;
uint32_t count = 0;

void setup() {
  Serial.begin(115200);
  pinMode(OBSTACLE_PIN, INPUT);  // the module has its own pull-up to VCC (3.3 V here)
  Serial.println("IR obstacle sensor on GPIO18 — wave a hand in front of it");
}

void loop() {
  bool blocked = digitalRead(OBSTACLE_PIN) == LOW;
  if (blocked && !lastBlocked) {
    count++;
    Serial.printf("Obstacle detected (#%lu)\n", (unsigned long)count);
  } else if (!blocked && lastBlocked) {
    Serial.println("Path clear");
  }
  lastBlocked = blocked;
  delay(10);
}

Expected serial output

IR obstacle sensor on GPIO18 — wave a hand in front of it
Obstacle detected (#1)
Path clear
Obstacle detected (#2)
Path clear

IR obstacle sensor on GPIO18 — wave a hand in front of it
Obstacle detected (#1)
Path clear
Obstacle detected (#2)
Path clear

Common errors