Project 2 - Measuring distance of an object using ultrasonic sensor (HC-SR04)

Here is the code

#define F_CPU 8000000UL    // Define the system clock frequency as 8 MHz
#include <avr/io.h>        // Include AVR input/output header file
#include <avr/interrupt.h> // Include AVR interrupt handling header file
#include <util/delay.h>    // Include delay header file
#include <string.h>        // Include string handling header file
#include <stdlib.h>        // Include standard library header file#define lcdport PORTB


#define lcdport PORTB      // Define LCD port as PORTB
#define rs_high PORTD |= (1<<0);   // Set RS pin high
#define rs_low PORTD &= ~(1<<0);   // Set RS pin low
#define en_high PORTD |= (1<<1);   // Set EN pin high
#define en_low PORTD &= ~(1<<1);   // Set EN pin low

static volatile int pulse =0;  // Declare a global variable for ultrasonic sensor
static volatile int i =0;     // Declare a global variable for ultrasonic sensor



// Interrupt service routine for INT0
ISR(INT0_vect)
{
	if (i==1)  // If i is 1
	{
		TCCR1B =0;    // Stop timer
		pulse = TCNT1;  // Store timer count in pulse variable
		TCNT1=0;    // Reset timer count to 0
		i=0;       // Reset i to 0
	}

	if (i==0)   // If i is 0
	{
		TCCR1B |=(1<<CS10);   // Start timer with no prescaling
		i=1;                 // Set i to 1
	}
}

// Function to send command to LCD
void lcd_cmd (unsigned char cmd)
{
	lcdport=cmd;    // Send command to LCD
	rs_low;         // Set RS pin low
	en_high;        // Set EN pin high
	_delay_ms(1);   // Delay for 1 millisecond
	en_low;         // Set EN pin low
}


// Function to send data to LCD
void lcd_data (unsigned char data)
{
	lcdport=data;   // Send data to LCD
	rs_high;        // Set RS pin high
	en_high;        // Set EN pin high
	_delay_ms(1);   // Delay for 1 millisecond
	en_low;         // Set EN pin low
}


void lcd_init()
{
	lcd_cmd(0x38);  // 8-bit mode, 2-line display, 5x8 font
	_delay_ms(5);   // Delay for 5 milliseconds
	lcd_cmd(0x02);  // Return home
	_delay_ms(5);   // Delay for 5 milliseconds
	lcd_cmd(0x01);  // Clear display
	_delay_ms(5);   // Delay for 5 milliseconds
	lcd_cmd(0x0c);  // Display on, cursor off
	_delay_ms(5);   // Delay for 5 milliseconds
	lcd_cmd(0x06);  // Entry mode: increment address, no display shift
	_delay_ms(5);   // Delay for 5 milliseconds
	lcd_cmd(0x80);  // Set DDRAM address to 0x00
	_delay_ms(5);   // Delay for 5 milliseconds
}

void lcd_print(char *str)
{
	unsigned char i=0;
	while (str[i]!=0)
	{
		lcd_data(str[i]);  // Send each character of the string to the LCD
		i++;               // Increment i
	}
}



int main(void)
{
	DDRD = 0x03;                // Set the direction of PORTD pins 0 and 1 as output
	// (to be used as trigger and LED pins)
	PORTD = 0xFF;               // Turn on pull-up resistor for all pins of PORTD
	GICR |= (1<<INT0);          // Enable external interrupt INT0
	MCUCR |= (1<<ISC00);        // Set interrupt triggering to occur when INT0 is low
	int16_t count_a = 0;        // Initialize variable to hold distance measurement
	char show_a[16];            // Initialize character array to hold distance measurement as string
	sei();                      // Enable global interrupts
	lcd_init();                 // Initialize the LCD
	lcd_print("Ultrasonic");    // Display "Ultrasonic" on the LCD
	_delay_ms(500);             // Wait for 500 milliseconds
	lcd_cmd(0x01);              // Clear the LCD
	lcd_print("Distance Sensor");// Display "Distance Sensor" on the LCD
	_delay_ms(500);             // Wait for 500 milliseconds

	while(1)                    // Start an infinite loop
	{
		PORTD |= (1<<PIND3);    // Set trigger pin high
		_delay_ms(15);          // Wait for 15 milliseconds
		PORTD &= ~(1<<PIND3);   // Set trigger pin low
		count_a = pulse/58;     // Calculate distance measurement from pulse duration
		_delay_ms(1000);        // Wait for 1 second
		lcd_cmd(0x01);          // Clear the LCD
		lcd_print("Distance: "); // Display "Distance: " on the LCD
		itoa(count_a, show_a, 10); // Convert distance measurement to string and store it in character array
		lcd_cmd(0xC0);          // Move cursor to second line of LCD
		lcd_print(show_a);      // Display distance measurement as string on the LCD
		lcd_cmd(0xC4);          // Move cursor to the end of second line on the LCD
		lcd_print("cm ");       // Display "cm " on the LCD
	}
}