[PIC] HC-SR04 ultrasonic sensor problem.

[ruben91]

can i know why my sensor cannot detect more than 230cm? perhaps in data sheet it stated can detect more than 400 cm.. im using pic18f4580 with 20Mhz crystal frequency

 

[paulfjujo]

hello,

what is your power supply voltage ?
show all your code ..
maybe your device is out of spec. or your code is not compliant for that.

 

[ruben91]

hello,currently im using 5v dc supply, this my code

#include <p18f4580.h>
#include <delays.h>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#pragma config OSC= HS
#pragma config WDT=OFF
#pragma config LVP=OFF

#define Trig PORTBbits.RB3
#define Echo PORTBbits.RB2

void T0Delay10us(void);
void T0Delay5ms(void);
void uart(void);
void Call_Init_PIC (void);
void sendPulse(void);

unsigned int distance ;
unsigned int time;
unsigned f,b;

void main(void)
{
TRISDbits.TRISD2=0;
TRISDbits.TRISD3=0;
TRISDbits.TRISD1=0;
TRISDbits.TRISD0=0;
Call_Init_PIC ();
uart();
while(1)
{
TMR1H= 0;
TMR1L= 0;
sendPulse();

while(Echo == 0);

T1CONbits.TMR1ON = 1;
while(Echo == 1);
T1CONbits.TMR1ON = 0;  

Delay10KTCYx(255);
Delay10KTCYx(255);
Delay10KTCYx(255);
Delay10KTCYx(255);                   

time= TMR1H;
time= time<<8;
time= time|TMR1L;
//time = (TMR1L + (TMR1H<<8));

distance = time/28.8;
f=distance/10;
b=distance%10;
printf("\r\nDistance = %d.%d cm",f,b);  
PIR1bits.TMR1IF=0;
Delay10KTCYx(255); 
T0Delay5ms(); 
/*
if(distance>=0 && distance<=250)
{
PORTDbits.RD2=1;
//printf("\ndangerous");
}

if(distance>=251 && distance<=500)
{
PORTDbits.RD3=1; 
}

if (distance>=501 && distance<=1000)
{
PORTDbits.RD0=1; 
}

if(distance>=1001)
{
PORTDbits.RD1=1;
//printf("\nsafe zone");
}
*/
}
}

void Call_Init_PIC (void)
{
TRISBbits.TRISB3=0;
TRISBbits.TRISB2=1;
}


void uart(void)
{
TXSTA=0B00100000;
SPBRG=32;
TRISCbits.RC6=0;
RCSTAbits.SPEN=1;
}


void sendPulse(void)
	{
	Trig=1;
	T0Delay10us();
	Trig=0;
	}


void T0Delay10us()
	{
	T0CON=0x08;
	TMR0H=0XFF;
	TMR0L=0XCE;
	T0CONbits.TMR0ON=1;
	while(INTCONbits.TMR0IF==0);
	T0CONbits.TMR0ON=0;
	INTCONbits.TMR0IF=0;
	}


void T0Delay5ms()
	{
	T0CON=0x08;
	TMR0H=0X9E;
	TMR0L=0X58;
	T0CONbits.TMR0ON=1;
	while(INTCONbits.TMR0IF==0);
	T0CONbits.TMR0ON=0;
	INTCONbits.TMR0IF=0;
	}

 

[Easyrider83]

When I tested this sensor a year ago with STM32 Discovery it shown the same result. About 2-3m range. Possible, china's meters are shorter as always? ))))

 

[paulfjujo]

hello,


Your code is correct but limited to a range of 2229 mm!
Time for sound move (in the air at 20°C) for 1mm is 2.94 µS =>5.88µS aller-retour
With Q=20Mhz Cycle is 4/20=>0.2µS
With timer0 16bits you can count a maxima of
65536*0.2=13107µS
corresponding displacement is 13107/5.88=> 2229 mm
after you have timer0 oveflow..
You need to take account oth this overflow,bit adding 65536 evrey time
Time1r interrupt flag is On..
so use a long int 32bits for time value..

unsigned long Over;
Unsigned long time;
....


while(1)
{

sendPulse();
T1CONbits.TMR1ON = 0;  
PIR1bits.TMR1IF=0;
TMR1H= 0;
TMR1L= 0;
Over=0;
time=0;

while(Echo == 0);
T1CONbits.TMR1ON = 1;
while(Echo == 1)
{
 if (PIR1bits.TMR1IF==1)
  {
     Over=Over+65536;
     PIR1bits.TMR1IF=0;
  }
}
T1CONbits.TMR1ON = 0;  

time= TMR1H;
time= time<<8;
time= time|TMR1L;
Distance= (time + Over)/58;    // <- don't forget travel of sound in both way forward then reverse

// or you can  use floating point calculus  to get distance in mm  distance/5.88

my application uses Capture CCP1 mode and i add air temperature coorection
you can see it on my web page.

 

[ruben91]

hello brother paulfjujo,

thank for enlighthing me, now i understand why my sensor can read up to 2 metres.

I have implemented ur coding in my project but i dun seem to get the result i wanted, now it jus can detect up to 80cm,
i have tested it same way i test previously in open space wit a box as an obstacle.

here i atached my result displayed in hyperterminal
<a title="Capture.PNG" href="http://obrazki.elektroda.pl/9948109700_1419570811.png"><img src="http://obrazki.elektroda.pl/9948109700_1419570811_thumb.jpg" alt="Capture.PNG" /></a>

 

[paulfjujo]

hello,


link to *.png is corrupted !..
add some intermediate printout of raw values to help for debugging
Sorry; if forgetted to tell you ,multiply counts by 0.2 to get result in µS !

unsigned long Over;
Unsigned int  time;
float Distance;


while(1)
{

sendPulse();
T1CONbits.TMR1ON = 0;  
PIR1bits.TMR1IF=0;
TMR1H= 0;
TMR1L= 0;
Over=0;
time=0;

while(Echo == 0);
T1CONbits.TMR1ON = 1;
while(Echo == 1)
{
 if (PIR1bits.TMR1IF==1)
  {
     Over=Over+65536;
     PIR1bits.TMR1IF=0;
  }
}
T1CONbits.TMR1ON = 0;  
time= TMR1H;
time= time<<8;
time= time|TMR1L;
printf("\r\nTime = %d",time);
printf("\r\nOver = %ul",Over); 
Distance=(float) time + (float) Over;
printf("\r\nTravel duration %4.1f µS",Distance); 
Distance=Distance*0.2/5.88;    // counts * 0,2µS / 5.88 => result in mm
printf("\r\nDistance %4.1f mm",Distance);