Ultrasonic Sensor HY-SRF05 One Pin Mode

The whole project is about measuring the distance between the sensor and an object in front of it. The goal is to check if a person passes through the area where the sensor is at. A super simple way to check if an area is trespassed ;)

To start with you need to run the code below:

const unsigned int TRIG_PIN=12;
const unsigned int ECHO_PIN=12;
const unsigned int BAUD_RATE=9600;

void loop () {}
void setup() {

 Serial.begin(BAUD_RATE);
 pinMode(TRIG_PIN, OUTPUT);
 digitalWrite(TRIG_PIN, LOW);
 delayMicroseconds(2);
 digitalWrite(TRIG_PIN, HIGH);
 delayMicroseconds(10);
 digitalWrite(TRIG_PIN, LOW);
 delayMicroseconds(2);

pinMode(ECHO_PIN, INPUT);
const unsigned long duration= pulseIn(ECHO_PIN, HIGH);
int distance= duration/29/2;

if(duration==0){
  Serial.println("Warning: no pulse from sensor");
  } 
 else{
     Serial.print("Distance: ");
     Serial.print(distance);
     Serial.print(" cm\n");
 }
delay(100);
}

So as to count the distance once and to show you how much it is. From then on you can use this in a loop:

const unsigned int TRIG_PIN=12;
const unsigned int ECHO_PIN=12;
const unsigned int BAUD_RATE=9600;

void setup() {}
void loop () {

 Serial.begin(BAUD_RATE);
 pinMode(TRIG_PIN, OUTPUT);
 digitalWrite(TRIG_PIN, LOW);
 delayMicroseconds(2);
 digitalWrite(TRIG_PIN, HIGH);
 delayMicroseconds(10);
 digitalWrite(TRIG_PIN, LOW);
 delayMicroseconds(2);

pinMode(ECHO_PIN, INPUT);
const unsigned long duration= pulseIn(ECHO_PIN, HIGH);
int distance= duration/29/2;

if(duration==0){
  Serial.println("Warning: no pulse from sensor");
  } 
if(distance <50){
  Serial.println("Warning: Somebody has breached the bunker!");
   }
 else{
     Serial.print("You are safe. For now...\n");
     }
delay(2000);
}

So as to check if somebody is in a hallway/doorway every 2 seconds. The amount of time between the loops can be changed via the:

delay(2000);

All done!