UltraSonic sensor reading varies at different baud rate.

Other Hardware Sensors
1

Hello! I have built my own code to interfacing ultrasonic(HC-SR04) sensor with Arduino/Genuino UNO board. It give correct reading at or below 9600 baud rate but when I change the baud rate above 9600 it goes crazy and the values come uneven.

Here's the code
sketch_dec21a

#include "US.h"
#include <SoftwareSerial.h>

uint16_t distance;
char gbuf[50];
int count;

void setup() {
  // put your setup code here, to run once:
  Serial.begin(38400);
  while (!Serial) {
    ; // wait for serial port to connect. Needed for native USB port only
  }

  // send an intro:
 ("UART Initialize");
  Serial.println();
  HC_SR04_Inti();
}

void loop() {
  // put your main code here, to run repeatedly:
  distance = HC_SR04_fun();
  sprintf(gbuf, "%d cm \r\n", distance);
  //Serial.println("HELLO\r\n");
  Serial.print(gbuf);
}

US.h

#ifndef __US_H_
#define __US_H_

/*
 * US_HC_SR04.c
 *
 * Created: 12/19/2016 11:38:57 AM
 * Author: Utpal
 * MCU: ATmega328
 */ 


#include <Arduino.h>
#include <util/delay.h>
#include <avr/interrupt.h>



static volatile uint16_t pulse = 0;
static volatile int ext_Int_count = 0;


void HC_SR04_Inti(void)
{
 DDRD |= 0b11111011;
  DDRD &= 0b11111011;
 _delay_ms(50);
 EIMSK &= (1 << INT0);
 EICRA |= (1 << ISC00);
 EIFR |= (1 << INTF0);
 EIMSK |= (1 << INT0);
 
 TCCR1A = 0; //Timer1 normal mode
 sei();    //Enable Global Interrupt 
  Serial.println("HC_SR04_Inti\r\n");
}



int16_t HC_SR04_fun(void)
{
 static uint16_t SR04_range = 0, avgSR04_range = 0; //Distance in cm
 int16_t  SR04_Read_count = 0;
 for(SR04_Read_count = 0; SR04_Read_count < 10; SR04_Read_count++)
 {
 PORTD |= (1 << PIND3); //trigger
 _delay_us(25);
 PORTD &= ~(1 << PIND3);
 SR04_range = pulse;
 SR04_range /= 116;
    //SR04_range /= 58;
 
 avgSR04_range += SR04_range;
 if(SR04_range <= 2){
 avgSR04_range = 0;
 return -1; //Minimum Range
 }
 if(SR04_range >= 350){
 avgSR04_range = 0;
 return -2; //Maximum Range
 }
 }
 avgSR04_range /= 10;
  return avgSR04_range;
}


ISR(INT0_vect)
{
 if (ext_Int_count == 1)
 {
 TCCR1B = 0; //TurnOff Timer1
 pulse = TCNT1;
 TCNT1 = 0;
 ext_Int_count = 0;
 }
 if (ext_Int_count == 0)
 {
 //TCCR1B |= (1 << CS10) | (1 << CS11); //TurnON Timer1 Clk/8 prescaler(CLK is 16MHz).
    TCCR1B |= (1 << CS11);  //TurnON Timer1 Clk/8 prescaler(CLK is 16MHz).
 ext_Int_count = 1;
 }
}

#endif

Here are readings at or below 9600 baud rate
112cm
116cm
117cm
117cm
116cm
116cm
116cm
117cm
116cm
116cm
116cm
116cm
116cm
116cm

These are readings above 9600 baud rate(at this time it's 38400 baud rate)
15 cm
117 cm
42 cm
35 cm
99 cm
24 cm
17 cm
16 cm
118 cm
37 cm
29 cm
102 cm
21 cm
13 cm
60 cm
14 cm
9 cm
8 cm
107 cm

Don't know what's wrong with my code.

Thank´s for help in advance and greetings

Utpal

2

How are we to help fix code that we can't see? The baud rate should have nothing to do with the rangefinder, so the code or your wiring is incorrect.

Please read the "how to use the forum" stickies to see how to format (ctrl-t) and post (code tags) code. Note the part about writing a small sketch that demonstrates the problem so we don't have to wade through pages of code.

3

Hello groundfungus. I have posted the code above. I don't know whether the issue is with code. If it's wrong then how do it work with 9600 or below baud rate.
Thanks for your reply.

4

Did you ever consider using one of the functioning libraries that are already available?

5

Hello npa62. Yeah I have written code using arduino libraries and that's working absolutely fine at all available baud rates. But I want to know that what's wrong in this code. Why it's malfunctioning at higher baud rates. As par algorithm Ultrasonic have nothing to do with baudrate.

6

What happens if you put a delay(30) at the end of loop()?

7

@AWOL yupzz it's working by adding 30ms delay. :slight_smile:
Thanks

8

Can you figure out why that is?

9

AWOL:
Can you figure out why that is?

I assume your response is rhetorical but I'd really like to know the answer. The only two suppositions I can suppose (and I have no background knowledge) are:

  1. the data transfer rate has increased so you can fit more readings in and it's picking up all of the echos from the table surface and more distant objects. Like a high precision low accuracy problem.

  2. I assumed the baud rate you chose was the measuring device's default rate. If not, could it be that you are trying to read between cycles and just getting garbage that's left in the registers?

I hope someone who knows can clarify!

10

The speed of sound is very very slow compared to a microcontroller. You can send dozens of characters
at 9600 baud in the time the ultrasound pulses are still rattling round the room. The 30ms delay provides time for the air in the room to recover.