adc problem in pic16f877a

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anjalimidhuna

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HI ALL,

I am doing my first project in pic. i have successfully completed the display portion. but can't do with adc. it always shows the same value. i am using pic16f877a and HI TECH C compiler. i want to display the ac voltage.i have selected AN2 for this.
 

hello,

i want to display the ac voltage
Click to expand...

what is the peak to peak value and frequency ?
Is the AC centered around zero volt or has a DC average value.
remenber ADC input is 0 to 5V .. so AC must be measured around +2,5V DC average
with AC amplitude of +-2,5V peak to peak .
 

HI paulfjujo,
thax for the rply.
i want to display the value of average ac from the mains ultimately(230V, 50 Hz). but now i just tried to display the instantaneous value which directly taken from the adc port pin. it always shows 9.
 

sankar.m8 said:
What is the ADC input signal voltage you have given (For getting the value 9 )?
Click to expand...

it always shows 9 even the signal is off
this is the code i used

Code C - [expand]
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/********************program to test adc functioning*********************/
#include<pic.h>
#include<htc.h>
#include<stdlib.h>
#include"lcdfn.h"
#include"ADC.h"
 
unsigned long value;
char *int_to_string(unsigned long int i, unsigned char buf[]);
void convert(unsigned long adc_value);
//MAIN STARTS HERE
void main()
{
    Lcd_Init();
    adc_init();
    LCD(Lcd_clear,ModCmd);
    Delay_ms(100);
    LCD(FstLin_FstColumn,ModCmd);
    while(1)
    {
    value=AdcRead(ch0);
    convert(value);
    }   
}
void convert(unsigned long adc_value)
{
unsigned int int_part,deci_part;
unsigned char strngIntPart[],strngDeciPart[];
unsigned char strngInt[4],strngDeci[4];
 
int_part=adc_value/100;
deci_part=adc_value%100;
 
int_to_string(int_part,strngIntPart);
int_to_string(deci_part,strngDeciPart);
 
Disp_STRING(strngIntPart);
LCD('.',ModData);
Disp_STRING(strngDeciPart);
}
 
char *int_to_string(unsigned long int i, unsigned char buf[])
{
    unsigned char temp;
    unsigned char s = 0,t = 0;
    while(i) 
    {
        buf[s++] = i % 10 + 0x30;
        i /= 10;
    }
    buf[s] = 0;
    s-=1;
    for(;t<s;t++,s--) 
    {
        temp = buf[s];
        buf[s]=buf[t];
        buf[t]=temp;
    }
    return buf;
}
 
Last edited by a moderator:

hello,

did you allready checked your "convert(value);" function..
with direct value assigned to the variable "value"..
to separate problems
ADC problem
or display problem
 

milan.rajik said:
Post code of ADCRead() function.
Click to expand... 

Code C - [expand]
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/*INITIALISE ADC*/
void adc_init()
{
    TRISA=0XFF;
    TRISE0=1;
    ADCON1=0X80;
}
 
/* READ ADC VALUES*/
unsigned char AdcRead()     
{
    ADCON0=0x55;
    while(GODONE==1);
    temp=((ADRESH<<8)+ADRESL);
    return temp;    
}
 
Last edited by a moderator:

hello


Code: 
unsigned char AdcRead()	
{
ADCON0=0x55;
while(GODONE==1);
temp=((ADRESH<<8)+ADRESL);
return temp;	
}

return value must be integer 16 bits not unsigned char
Where is defined temp ?
in the main you use a long int to receive result of AdcRead..
so
Code: 
[B]unsigned int [/B]AdcRead()	
{
[B]unsigned int temp;[/B]
ADCON0=0x55;
while(GODONE==1);
temp=((ADRESH<<8)+ADRESL);
return temp;	
}
 


i have made the correction.but now it only shows '.' i think the problem is with my convert(value) function..
 

"9" means 9V or the hex code "1001" ? How many bit is the ADC ? If you have not properly terminate the ADC channel, you may get some noise. Try reading by grounding the ADC input.
 

Actually problem is with my code.. i got the correct result by using micro C using i built function. now i am trying to make it my own in mplab. but it doesn't work.
 

hello,


in your conv to string routine, you use an undefined table instead of a pointer of this table

first declare the table wich receive the chars

unsigned char buf[16];

and modify the function

Code: 
char *int_to_string(unsigned long int i, unsigned char* buf)
{
    unsigned char temp;
    unsigned char s = 0,t = 0;
    while(i) 
    {
        buf[s++] = i % 10 + 0x30;
        i /= 10;
    }
 buf[s] = 0;
    s-=1;
    for(;t<s;t++,s--) 
    {
        temp = buf[s];
        buf[s]=buf[t];
        buf[t]=temp;
    }
    return buf;
}

it's works !!! tested with C18 MPLAB


Code: 
Value=513;int_to_string(Value, buf);
 k=fprintf(_H_USART,(const rom unsigned char *)"ADC= %ld    %s\r\n",Value,buf); 
 
Value=1023;
int_to_string(Value, buf);
 k=fprintf(_H_USART,(const rom unsigned char *)"ADC= %ld    %s\r\n",Value,buf); 


Value=Mesure_ADC(0);
int_to_string(Value, buf);
 k=fprintf(_H_USART,(const rom unsigned char *)"ADC= %ld    %s\r\n",Value,buf); 
 CRLF()

gives this result on terminal

ADC= 513 513
ADC= 1023 1023
ADC= 224 224
Click to expand...

int_to_string(Value, buf); is enough to get the result ...
Why using long for value , result of ADC measure... maximum is 1023
integer size is enough.

or rename function as

long_to_string(Value,buf);
 
Last edited:

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