Arduino sketch to scan for I2C addresses

i2c-detect.ino

/*
 * i2c-detect.ino
 * just like the Linux utility
 *
 * 2016.01.09 darell tan
*/

#include <Wire.h>

int led_pin = 13;
int start_addr = 0;

void setup() {
  Wire.begin();

  Serial.begin(9600);
  Serial.println("begin!");

  pinMode(led_pin, OUTPUT);

  // lets you open up the console
  delay(2000);
}

void loop() {
  // use built-in LED to indicate working status
  digitalWrite(led_pin, (start_addr % 2) == 0);

  Wire.beginTransmission(start_addr);
  Wire.write(0x00);
  int n = Wire.endTransmission();
  if (n == 0) {
    Serial.print("found addr! 0x");
    Serial.print(start_addr, HEX);
    Serial.println();
  }
  start_addr++;

  // once start_addr becomes 8-bit, hang here
  if (start_addr == 0x80) {
    Serial.println("finished scanning.");
    start_addr = 0; // reset
  }

  delay(50);
}