Reading From ADC atmega32

[Bluestar88]

i am using Atmega32 ADC to measure a 5V analog voltage.
i want to make an ADC conversation using ADMUX=0x40 (AVCC ref.) So I used the below code and I attached the AREF pin(number pin=32)to VCC. (I used the putchar() becauuse I want to send the value to visual basic(PC))

unfortunately it's not working and the results keep changing without any changes in the voltages (the value which I measure doesnot change)...can i get some HELP please?......

#include <mega32.h>

// Standard Input/Output functions
#include <stdio.h>
#include <delay.h>
#include <math.h>



// Read the AD conversion result
unsigned char i=0;
unsigned int read_adc(unsigned char adc_input)
{
unsigned char t;
ADMUX=adc_input | (ADC_VREF_TYPE & 0xff);
// Delay needed for the stabilization of the ADC input voltage
delay_us(10);
// Start the AD conversion
ADCSRA|=0x40;
// Wait for the AD conversion to complete
while ((ADCSRA & 0x10)==0);
ADCSRA|=0x10;
//t=ADCW;
//t=((ADCW*2.56)/1023)*100;
t=((ADCW*5)/1023);
return t;
}


void main( )
{

ADMUX=ADC_VREF_TYPE & 0xff;
ADCSRA=0x86;


while (1)
      {   
        
        if (a=='$')
         {
          
          i=1;
           adc_value=read_adc(i);    
           PORTB=adc_value;
           putchar(adc_value);
           delay_ms(10); 
          
         }    
   }
}

 

[KlausST]

Hi,

Please specify "the value is changing".

+/- 1LSB one can not avoid.
With a 10bit ADC it should be stable within this range.
If the change is more than that, then there are a lot of possible problems. Ranging from software problems, setup problems, hardware problems....

To give you better assistance we need mor information..

Klaus

 

[Bluestar88]

I used 8bit ADC, and AVCC(5volt)as a v Refrence....
but for two input which are 0 and 2.5 volt the ADC measures 1.5 and 2.1, respectively...I donot why..please help me..the code is here...

#include <mega32.h>
#include <stdio.h>
#include <delay.h>
#include <math.h>
#define CLBR 0x33 


#define ADC_VREF_TYPE 0x60
///////////////////////////////////////////////////////////////
// Read the AD conversion result
unsigned char i=0;
unsigned int read_adc(unsigned char adc_input)
{
//unsigned char t;

ADMUX=adc_input | (ADC_VREF_TYPE & 0xff);
// Delay needed for the stabilization of the ADC input voltage
delay_us(10);
// Start the AD conversion
ADCSRA|=0x40;
// Wait for the AD conversion to complete
while ((ADCSRA & 0x10)==0);
ADCSRA|=0x10;
//t=((ADCW*5)/255); 
//t=((ADCW*2.56)/1023)*100;
//t=((ADCW*5)/1023);
return ADCW;
}


void main( )
{
char a=0;

unsigned char adc_value;

UCSRA=0x00;
UCSRB=0x18;
UCSRC=0x86;
UBRRH=0x00;
UBRRL=0x19;


SFIOR=0x00;
ADMUX=ADC_VREF_TYPE & 0xff;
ADCSRA=0x84;

while (1)
      {   
     
   a=getchar();
 if (a=='$')
         {
          
          i=1;
           adc_value=read_adc(i); 
           putchar(ADCH);
           //PORTB=ADCH;
           delay_ms(10); 
          
         }    
        

  } 
  
  }