08_example_2.ino

// Arduino pin assignment
#define PIN_LED 9
#define PIN_TRIG 12
#define PIN_ECHO 13

// configurable parameters
#define SND_VEL 346.0 // sound velocity at 24 celsius degree (unit: m/s)
#define INTERVAL 25 // sampling interval (unit: ms)
#define _DIST_MIN 100 // minimum distance to be measured (unit: mm)
#define _DIST_MAX 300 // maximum distance to be measured (unit: mm)

// global variables
float timeout; // unit: us
float dist_min, dist_max, dist_raw; // unit: mm
float last_raw;
unsigned long last_sampling_time; // unit: ms
float scale; // used for pulse duration to distance conversion

void setup() {
// initialize GPIO pins
  pinMode(PIN_LED,OUTPUT);
  pinMode(PIN_TRIG,OUTPUT);
  digitalWrite(PIN_TRIG, LOW); 
  pinMode(PIN_ECHO,INPUT);

// initialize USS related variables
  dist_min = _DIST_MIN; 
  dist_max = _DIST_MAX;
  timeout = (INTERVAL / 2) * 1000.0; // precalculate pulseIn() timeout value. (unit: us)
  dist_raw = 0.0; // raw distance output from USS (unit: mm)
  last_raw = 0.0;
  scale = 0.001 * 0.5 * SND_VEL;

// initialize serial port
  Serial.begin(57600);

// initialize last sampling time
  last_sampling_time = 0;
}

void loop() {
// wait until next sampling time. 
// millis() returns the number of milliseconds since the program started. Will overflow after 50 days.
  if(millis() < last_sampling_time + INTERVAL) return;

// get a distance reading from the USS
  dist_raw = USS_measure(PIN_TRIG,PIN_ECHO);

// output the read value to the serial port
  Serial.print("Min:0,");
  Serial.print("raw:");
  
  // turn on the LED if the distance is between dist_min and dist_max
  if (dist_raw < dist_min || dist_raw > dist_max) {
    dist_raw = last_raw;
    Serial.print(dist_raw);
    analogWrite(PIN_LED, LED_light(dist_raw));
  }
  else {
    Serial.print(dist_raw);
    analogWrite(PIN_LED, LED_light(dist_raw));
  }
  Serial.print(",");
  Serial.println("Max:400");

  last_raw = dist_raw;
// update last sampling time
  last_sampling_time += INTERVAL;
}

// get a distance reading from USS. return value is in millimeter.
float USS_measure(int TRIG, int ECHO)
{
  float reading;
  digitalWrite(TRIG, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG, LOW);
  reading = pulseIn(ECHO, HIGH, timeout) * scale; // unit: mm
  if(reading < dist_min || reading > dist_max) reading = 0.0; // return 0 when out of range.
  return reading;
  // Pulse duration to distance conversion example (target distance = 17.3m)
  // - round trip distance: 34.6m
  // - expected pulse duration: 0.1 sec, or 100,000us
  // - pulseIn(ECHO, HIGH, timeout) * 0.001 * 0.5 * SND_VEL
  //           = 100,000 micro*sec * 0.001 milli/micro * 0.5 * 346 meter/sec
  //           = 100,000 * 0.001 * 0.5 * 346 * micro * sec * milli * meter
  //                                           ----------------------------
  //                                           micro * sec
  //           = 100 * 173 milli*meter = 17,300 mm = 17.3m
  // pulseIn() returns microseconds.
}

float LED_light(float dist_raw)
{
  int light;
  if ((dist_raw < 210)&&(dist_raw > 190)) {
    light = 0;
  }
  else if ((dist_raw < 160)&&(dist_raw > 140)) {
    light = 127;
  }
  else if ((dist_raw < 260)&&(dist_raw > 240)) {
    light = 127;
  }
  else if ((dist_raw < 120)&&(dist_raw > 100)) {
    light = 250;
  }
  else if ((dist_raw < 300)&&(dist_raw > 280)) {
    light = 250;
  }
  else if (dist_raw == 0) {
    light = 255;
  }
  else if ((dist_raw < 140)&&(dist_raw > 120)) {
    light = 200;
  }
  else if ((dist_raw < 280)&&(dist_raw > 260)) {
    light = 200;
  }
  else {
    light = 60;
  }
  return light;
}