HC-SR04 Ultrasonic Sensor with LED feedback

1#define echoPin 8 // echo pin connected to pin 8 
2#define trigPin 9  // trig pin connected to pin 9 
3#define RED 5 // red led connected to pwm pin  5
4#define GREEN 6 // green led connected to pwm pin 6 
5
6int time;
7int  dist; 
8const int MAX_DIST = 400; // Anything over 20 cm (120us pulse) is "out  of range"
9char outputValue; //8bit 0 to 255
10
11void setup() {
12  pinMode(trigPin,  OUTPUT); // Sets the trigPin as an OUTPUT
13  pinMode(echoPin, INPUT); // Sets  the echoPin as an INPUT
14  pinMode(RED, OUTPUT);
15  pinMode(GREEN, OUTPUT);
16  Serial.begin(9600);//start serial monitor
17}
18
19void loop() {
20  // trigger  sensor for 10us pulse
21  digitalWrite(trigPin, LOW); //reset trig condition 
22  delayMicroseconds(2);
23  digitalWrite(trigPin, HIGH); // set trig HIGH for 10  us
24  delayMicroseconds(10);
25  digitalWrite(trigPin, LOW); // return to LOW
26  
27  // read echo pin, output in us
28  time = pulseIn(echoPin, HIGH);
29  
30  // Calculate distance in cm
31  dist = time * 0.0343 / 2; // time * speed of  sound through air, divided by 2 (pulse is there and back)
32  outputValue = map(dist,  0, MAX_DIST, 0, 255); //map int to 8 char 
33  
34  Serial.print("Distance: ");//Prints  distance in serial monitor
35  Serial.print(dist);
36  Serial.println(" cm");
37  
38  if (dist < MAX_DIST){
39    analogWrite(RED, outputValue); // more red  when close
40    analogWrite(GREEN, 255 - outputValue); // more green when far  away
41  }
42
43  else{
44    analogWrite(RED, 255);
45    analogWrite(GREEN,  255); 
46  }
47
48}
49