Basic Example - How to use Ultrasonic SR04 distance sensor with Atmega8 and Timer0 (8Mhz)

Ultrasonic_SR04_Atmega8_8Mhz_Timer0_Basic_Example.c

// Notice: 8 Mhz frequency is expected

#define SONIC_DDR DDRC
#define SONIC_PORT PORTC
#define SONIC_PIN PINC
#define SONIC_TRG_PIN PINC0
#define SONIC_ECHO_PIN PINC1

#include <avr/io.h>
#include <util/delay.h>

// Setup sonic pins
void sonic_init(void) {
	SONIC_DDR |= 1 << SONIC_TRG_PIN; // Set trigger PIN to output
	SONIC_PORT &= ~(1 << SONIC_TRG_PIN); // Set trigger PIN to low
	SONIC_DDR &= ~(1 << SONIC_ECHO_PIN); // Set echo PIN to input
}

// Get the distance
// By using timer0 and 8Mhz clock maximum calculated distance is ~139 CM
uint8_t sonic_get_distance_cm(void) {
	// Trigger sensor measurement
	SONIC_PORT |= (1 << SONIC_TRG_PIN);
	_delay_us(10);
	SONIC_PORT &= ~(1 << SONIC_TRG_PIN);

	// Wait until echo goes up
	while(((SONIC_PIN >> SONIC_ECHO_PIN) & 1) == 0);
	
	// Calculate distance by calculating response time
	TCNT0 = 0; // Reset timer0
	TCCR0 |= 1 << CS02; // Start timer0 (256)

	// Wait until echo goes low or timer0 overflow occurred
	while(((TIFR >> TOV0) & 1) == 0 && ((SONIC_PIN >> SONIC_ECHO_PIN) & 1) == 1);

	TCCR0 = 0; // Stop timer0

	// If overflow occurred then return 255
	if ((TIFR >> TOV0) & 1) {
		TIFR |= 1 << TOV0;
		return 255;
	}

	// Return calculated distance
	return TCNT0 * 0.5488; // 0.000032 * (34300 * 0.5) = 0.5488
}

int main(void)
{
	sonic_init();
	
	uint8_t dist_cm;

	while (1)
	{
		dist_cm = sonic_get_distance_cm();
		
		// TODO: Use the "dist_cm" variable distance as you want
		
		_delay_ms(333);
	}
}