Ultrasonic sensor interfacing with AVR

Question

I'm working on a project part of it to have some reads with ultrasonic sensor and send it with serial communication, i wrote code and it gives random reads and sometimes gives 0 as a read, is the formula i used for finding distance right !?, or there is another formula, I'm using Atmega32 with internal 8MHz clock, can someone help me and know what's wrong with my code !?.

#define F_CPU 8000000UL
#include <avr/io.h>
#include <util/delay.h>
#include <avr/interrupt.h>

void inti_serial();

static volatile int pulse = 0;
static volatile int change = 0;

int main(void)
{ 

/* Replace with your application code */
inti_serial();

MCUCR |= (1 << ISC00); //Any logical change on INT0
GICR |= (1 << INT0); //Enable INT0

TCCR1A=0;
sei();

while (1) 
{
PORTC |= (1<<0);
_delay_us(15);
PORTC &= ~(1<<0);
while(!(UCSRA & (1<<UDRE)));
UDR = ((pulse/2)*1*(1/F_CPU)*343) ;
_delay_ms(100);
}
}

ISR(INT0_vect){


if (change==1)//when logic from HIGH to LOW

{

    TCCR1B=0;//disabling counter

    pulse=TCNT1;//count memory is updated to integer

    TCNT1=0;//resetting the counter memory

    change=0;

}

if (change==0)//when logic change from LOW to HIGH

{

    TCCR1B|=(1<<CS10);//enabling counter

    change=1;

}
}

void inti_serial()
{
 UCSRB |= (1<<TXEN);
 UCSRC |= (1<<UCSZ0) | (1<<UCSZ1) | (1<<URSEL);
 UBRRL = 0x33;
}

Possible duplicate of [Serialize Data Structures in C](https://stackoverflow.com/questions/371371/serialize-data-structures-in-c) — Gianluca Ghettini, Oct 19 '17 at 14:59
@GianlucaGhettini This question has nothing to do with serialization but, remotely, with *serial communication*. — JimmyB, Oct 19 '17 at 15:14

score 1 · Accepted Answer · answered Oct 19 '17 at 14:09

I see a few options for improvement in your development:

You are writing a sample from the ISR to variable and you read it continuously from the main loop and output it. Instead you should only output a new sample once (makes the serial data much smaller and easier to concentrate on the actual content and sample timing)
Before you think about the correct formula you should verify that your sampling mechanism is right. Without details about your sensor, nobody here can judge your formula, anyway.
Instead of sampling a free running counter you could use the input capture circuit of the processor (more accurate, less jitter due to interrupt latency)
Instead of resetting the counter register to zero you could subtract two consecutive samples from each other (less sample jitter due to interrupt latency)
Instead of deducing the edge from a toggled flag, ask the hardware about the state of the pin or which edge triggered the interrupt (or the capture)

Ultrasonic sensor interfacing with AVR

1 Answers1