8051 tacho

I,ve made a "tacho" using an 8051 , a 4511 decoder and 4 digit 7 seg display. its not very accurate where am i going wrong with my code.

Code:

#include <reg66x.h>

#define on 1
#define off 0

void delay();

unsigned int F,number,i,count,overflow,digit1,digit2,digit3,digit4;
 float T;

sbit enable_digit1 = P1^0;
sbit enable_digit2 = P1^1;
sbit enable_digit3 = P1^2;
sbit enable_digit4 = P1^3;

void an_interrupt() interrupt 0 using 1
{
 TR0 =on;
  if (count<3)
  {count++;}
  else
   TR0 = off;
   T = overflow* 65536 ;
   T = T + ( TH0 *256 ) + TL0 ;
   T = T * 0.000000543;
   F = 1/T;
   number = F * 60 ;
   digit1 = (number/1000);
   digit2 = ( (number%1000)/100 );
   digit3 = ( (number%100)/10 );
   digit4 = ( (number%10) );
   count = 0;
   overflow = 0;
   TH0 = 0x00;
  TL0 = 0x00;
    }

void timing ()interrupt 1 using 2
 {
  overflow++;
 }

void main (void)
{
  count = 0; // set count zero
  IT0 =on;  // make interrupt edge triggered
  TMOD = 0x01;   //mode 1
  TH0 = 0x00;
  TL0 = 0x00;
  TR0 = off; //timer0 off
  EA = on;   //global enable all
  ET0 = on;  //enable timer zero
  EX0 = on;    //enable external interrupt
 
  while (on)
    {
   P2 = digit1;         //multiplex digits on and off
   enable_digit1 = on;
   delay();
   enable_digit1 = off;
   P2 = digit2;
   enable_digit2 = on;
   delay();
   enable_digit2 = off;
   P2 = digit3;
   enable_digit3 = on;
   delay();
   enable_digit3 = off;
   P2 = digit4;
   enable_digit4 = on;
   delay();
   enable_digit4 = off;
    }
}


void delay()
   {
     for(i=0; i<255; i++)
    {
    }
   }

How large in bits is an "unsigned int" on your micro-controller?
I think you are overflowing it with this statement "T = overflow* 65536 ;"

Correction, I was right the first time. Try casting by using this code.

Code:

T = (float)overflow* 65536 ;

Is the value you are getting too large or too small? Or both?


Tim S.

Thanks for pointing that out. i'll give it a try as soon as i can.
Any more advice is more than welcome. Thanks again

The value shown on the dislay is too high and is fluctuating

> else
> TR0 = off;
> T = overflow* 65536 ;
Your indentation suggests that the whole code should belong to the else, but in reality, only one line is part of the else.

Everything else happens all the time (possibly fluctuating).

ALWAYS use braces, then you always know what you mean.

ive changed code a little values on the display are changing by 60 each time, the reading are quite good between 1-5Hz and 56 -165 Hz Between 5 to 56 the reading fluctuates

Code:

#include <reg66x.h>
#define on 1
#define off 0

void delay();

unsigned int number,i,count, digit1,digit2,digit3,digit4;
float T,F,overflow;

sbit enable_digit1 = P1^0;
sbit enable_digit2 = P1^1;
sbit enable_digit3 = P1^2;
sbit enable_digit4 = P1^3;

void an_interrupt() interrupt 0 using 1
  {
  TR0 = on;
  if (count == 0)
    {
     count++;}
  else
  {
  TR0 = off;
   T = overflow* 0x10000 ;
   T = T + ( TH0 *256 ) + TL0 ;
   T = T * 0.000000543;
   F = 1/T;
   number = F * 60* count ;
   digit1 = (number/1000);
   digit2 = ( (number%1000)/100 );
   digit3 = ( (number%100)/10 );
   digit4 = ( (number%10) );
   count = 0;
   overflow = 0;
   TH0 = 0x00;
  TL0 = 0x00;
   
  }
}

void timing ()interrupt 1 using 2
 {
  overflow++;
 }

void main (void)
{
  count = 0; 
  IT0 =on;    
  TMOD = 0x01;   
  TH0 = 0x00;
  TL0 = 0x00;
  TR0 = off; 
  EA = on;   
  ET0 = on;  
  EX0 = on;    
  
  while (on)
    {
  

   P2 = digit1;         
   enable_digit1 = on;
   delay();
   enable_digit1 = off;
   P2 = digit2;
   enable_digit2 = on;
   delay();
   enable_digit2 = off;
   P2 = digit3;
   enable_digit3 = on;
   delay();
   enable_digit3 = off;
   P2 = digit4;
   enable_digit4 = on;
   delay();
   enable_digit4 = off;
    }
}


void delay()
   {
     for(i=0; i<55; i++)
    {
    }
   }

The display is now not jumping up in steps of sixty, but using an input signal of less than 60 Hz, i am still getting the wrong readings on the display.Could this be due to the micro I am using

Well you did multiply by 60 for some reason.