#include<LiquidCrystal.h>
LiquidCrystal lcd(2, 3, 4, 5, 6, 7);

#define echo A0    //Echo pin
#define trigger A1 //Trigger pin

#define Recheck A5 // choose the pin for the Recheck button

#define G_led 8 // choose the pin for the Green Led
#define R_led 9 // choose the pin for the Red Led
#define buz  10 // choose the pin for the Buzzer

// defines variables
float Speed=0, distance=0, Time=0;
int flag1=0, flag2=0;
int time1, time2;

// Other configuration
const unsigned int BEEP_FREQUENCY = 3000;

void setup(){
pinMode(Recheck, INPUT_PULLUP);

pinMode(echo, INPUT );// declare ultrasonic sensor Echo pin as input
pinMode(trigger, OUTPUT); // declare ultrasonic sensor Trigger pin as Output 

pinMode(R_led,OUTPUT); // declare Red LED as output
pinMode(G_led,OUTPUT); // declare Green LED as output
pinMode(buz,OUTPUT);   // declare Buzzer as output

lcd.begin(16,2);
lcd.clear();
lcd.setCursor(0,0);
lcd.print(" Vehicle  Speed ");
lcd.setCursor(0,1);
lcd.print("   Measurement  ");
delay(2000);
lcd.clear();
}

void loop(){
ultrasonicRead(); //calls ultrasoninicRead() function below

if(distance<=30 && flag1==0){time1 = millis(); flag1=1;}
if(distance<=20 && flag2==0){time2 = millis(); flag2=1;}

if(flag1==1 && flag2==1){flag1=2, flag2=2;
     if(time1 > time2){Time = time1 - time2;}
else if(time2 > time1){Time = time2 - time1;}
 Time=Time/1000;//convert millisecond to second
 Speed=(10/Time);//v=d/t
 Speed=Speed*3600;//multiply by seconds per hr
 Speed=Speed/1000;//division by meters per Km

digitalWrite(R_led, 0);
digitalWrite(G_led, 1);
tone(buz, BEEP_FREQUENCY, 200);  // Beep when done
}

if(digitalRead(Recheck)==0){
Speed=0;
flag1=0, flag2=0;
digitalWrite(R_led, 1);
digitalWrite(G_led, 0);
tone(buz, BEEP_FREQUENCY, 400);  // Beep when done
}

lcd.setCursor(0,0);
lcd.print("Dist. in cm ");
lcd.print(distance);
lcd.print("   ");

lcd.setCursor(0,1); 
lcd.print("Speed Km/Hr ");
lcd.print(Speed); 
delay(10);   
}

void ultrasonicRead(){
digitalWrite(trigger, LOW); //PULSE ___|---|___
delayMicroseconds(2); 
digitalWrite(trigger, HIGH); 
delayMicroseconds(10); 
long time = pulseIn(echo, HIGH); 
distance = time / 28.5 / 2;
}