Parking sensor

1/**************************************************************
2 *  PARKING SENSOR WITH HC-SR04                               *
3 *                                                            *
4  *  This code receives data from the HC-SR04 proximity        *
5 *  sensor, analyses  them, sends them to the serial monitor   *
6 *  and produces intermittent sounds  to warn of an obstacle.  *
7 **************************************************************/
8
9//  Definition of trigger, echo, beep pins and other constants
10#define trigger      2
11#define  echo         3
12#define beep        11
13#define beep_start 100
14#define min_distance  5
15
16// Definition of sound speed (centimetres / microsecond)
17#define c 0.0343
18
19//  Definition of the variables
20long tempo;
21float space;
22
23void setup() {
24  // Definition of input and output
25  pinMode(trigger, OUTPUT);
26  pinMode(echo,  INPUT);
27  pinMode(beep, OUTPUT);
28
29  // Serial communication initialisation  (optional)
30  Serial.begin(9600);
31}
32
33void loop() {
34  // Before measurement,  the trigger is set to low level
35  digitalWrite(trigger, LOW);
36  delayMicroseconds(5);
37
38  // Send one pulse (trigger goes high level for 10 microseconds)
39  digitalWrite(trigger,  HIGH);
40  delayMicroseconds(10);
41  digitalWrite(trigger, LOW);
42
43  //  Reading echo, via pulseIn, which returns the duration of the impuse (in microseconds)
44  // The acquired data is then divided by 2 (forward and backward)
45  tempo =  pulseIn(echo, HIGH) / 2;
46  // Computation of distance in centimetres
47  space  = tempo * c;
48
49  // space is displayed in the serial monitor ([Ctrl] + [Shift]  + M)
50  // approximated to the first decimal place
51  Serial.println("Distanza  = " + String(space, 1) + " cm");
52
53  // If the distance is less than one  metre
54  if (space < beep_start) { 
55    // Emits sounds at intervals proportional  to distance (1 m = 400 ms)
56    tone(beep, 1000); 
57    delay(40);
58    //  Below min_distance cm it emits a continuous sound
59    if (space > min_distance)  {
60      noTone(beep); 
61      delay(space * 4);
62    }
63  } 
64  // Waits  50 milliseconds before another measurement
65  delay(50);
66}