Arduino Robot with Temp, Ultrasonics, and Flammable Gas

#include <dht.h>

dht DHT;

#define DHT11_PIN 5



const int trigPin = 2;

const int echoPin = 4;

const int sensorPin= 0;

const int buzzerPin= 13;

int smoke_level;



void setup() {
  
Serial.begin(9600);
 //sets the baud rate for data transfer in bits/second
  
pinMode(sensorPin, INPUT);//the smoke sensor will be an input to the arduino
  
pinMode(buzzerPin, OUTPUT);//the buzzer serves an output in the circuit
}


void loop()
{
  // establish variables for duration of the ping, 
  // and the distance result in inches and centimeters:
    int chk = DHT.read11(DHT11_PIN);
long duration, inches, cm;

  // The sensor is triggered by a HIGH pulse of 10 or more microseconds.
  
// Give a short LOW pulse beforehand to ensure a clean HIGH pulse:
  
pinMode(trigPin, OUTPUT);
 
 digitalWrite(trigPin, LOW);
 
 delayMicroseconds(2);
  
digitalWrite(trigPin, HIGH);
  
delayMicroseconds(10);
 
 digitalWrite(trigPin, LOW);

  // Read the signal from the sensor: a HIGH pulse whose
  // duration is the time (in microseconds) from the sending
  // of the ping to the reception of its echo off of an object.
 
 pinMode(echoPin, INPUT);
  
duration = pulseIn(echoPin, HIGH);

  // convert the time into a distance

  inches = microsecondsToInches(duration);

  cm = microsecondsToCentimeters(duration);
  
 
 smoke_level= analogRead(sensorPin); //arduino reads the value from the smoke sensor

Serial.println(smoke_level);//prints just for debugging purposes, to see what values the sensor is picking up
 
 
 Serial.print(inches);
 
 Serial.print("in, ");
 
 Serial.print(cm);
  
Serial.print("cm");
  
Serial.println();

   Serial.print("humidity = ");
  Serial.println(DHT.humidity,1);
  Serial.print("temperature = ");
  Serial.println(DHT.temperature,1);
  
 
 if(smoke_level > 170){ //if smoke level is greater than 170, the buzzer will go off
    
digitalWrite(buzzerPin, HIGH);
     }
   
else{
    
digitalWrite(buzzerPin, LOW);
   
 }
  
 
 delay(150);
}




/////////////////////////////////////////// FUNCTIONS ////////////////////////////////////////


long microsecondsToInches(long microseconds)

{
  // According to Parallax's datasheet for the PING))), there are
  // 73.746 microseconds per inch (i.e. sound travels at 1130 feet per
  // second).  This gives the distance travelled by the ping, outbound
  // and return, so we divide by 2 to get the distance of the obstacle.
  // See: http://www.parallax.com/dl/docs/prod/acc/28015-PING-v1.3.pdf
  return microseconds / 74 / 2;
}

long microsecondsToCentimeters(long microseconds)
{
  // The speed of sound is 340 m/s or 29 microseconds per centimeter.
  // The ping travels out and back, so to find the distance of the
  // object we take half of the distance travelled.
  return microseconds / 29 / 2;
}