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problem in analog to digital convertion in atmega 8

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selva murugesan

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what is wrong with this following code? i am using 1Mhz clk



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void adc_init (void);
int adc_read (unsigned char ch_select);
 
void adc_init (void)
{
    ADCSRA |= 0x83;
}
 
int adc_read (unsigned char ch_select)
{
    int tenbit_value,adc_low;
    ADMUX |= ch_select;
 
    ADCSRA = ADCSRA | (1<<ADSC);    // Start ADC conversion
    while(!(ADCSRA & (1<<ADIF)))    // Wait for AD interrupt flag 
    adc_low = ADCL;
 
    tenbit_value = (ADCH << 2 | adc_low>>6); 
    ADCSRA.ADSC |= 0;
 
    return tenbit_value;
}

there is show no error.but i cant get output.
 
Last edited by a moderator:

this is how i do it !
Code: 
void InitADC()
{
ADMUX=(1<<REFS0);                  // For Aref=AVcc;
ADCSRA=(1<<ADEN)|(1<<ADPS2)|(1<<ADPS1)|(1<<ADPS0);
}

uint16_t ReadADC(char ch_select)
{
   ADMUX |= ch_select;  
   ADCSRA|=(1<<ADSC);
   while(!(ADCSRA & (1<<ADIF)));
   ADCSRA|=(1<<ADIF);
   return(ADC);
}

hope this will help you
 

selva murugesan said:
what is wrong with this following code? i am using 1Mhz clk



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void adc_init (void);
int adc_read (unsigned char ch_select);
 
void adc_init (void)
{
    ADCSRA |= 0x83;
}
 
int adc_read (unsigned char ch_select)
{
    int tenbit_value,adc_low;
    ADMUX |= ch_select;
 
    ADCSRA = ADCSRA | (1<<ADSC);    // Start ADC conversion
    while(!(ADCSRA & (1<<ADIF)))    // Wait for AD interrupt flag 
    adc_low = ADCL;
 
    tenbit_value = (ADCH << 2 | adc_low>>6); 
    ADCSRA.ADSC |= 0;
 
    return tenbit_value;
}

there is show no error.but i cant get output.
Click to expand...

Since your ATmega8 is running at 1MHz there are 2 valid ADC clock frequencies you can select:
125KHz and 62.5kHz

If you want to run the ADC at 125kHz you can initialize it this way:
ADCSRA = _BV(ADEN) | _BV(ADPS1) | _BV(ADPS0);
This expression is similar to
ADCSRA = (1 << ADEN) | (1 << ADPS1) | (1 << ADPS0);
and
ADCSRA = 0x83;

Publish the whole code with main and circuit if you want detailed help

---------- Post added at 14:56 ---------- Previous post was at 14:50 ----------

https://extremeelectronics.co.in/avr-tutorials/using-the-analog-to-digital-converter/

---------- Post added at 14:56 ---------- Previous post was at 14:56 ----------

https://extremeelectronics.co.in/avr-tutorials/using-the-analog-to-digital-converter/
 

here i have phased main() program. my task is get 2 analog value from out side,change into corresponding decimal value and finally ,show the values in 6 (7 segments display) as (0-999) format.here, i used max 7219 interface for LED driver.the header files of the SPI and max 7219 are download from net

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#include <mega8.h>
#include <delay.h>
#include <macros.h>
#include <ADC_EDT_10bit.H>
#include <spi_header.h>
#include <max7219.h>
 
#define mul 199.8
//display test normal mode
 
 
 
// Declare your global variables here
unsigned char w,x,y,z;
unsigned char flag;
int adc_result1,adc_result2,i;
int adc_display1,adc_display2;
 
 
void adc_read_in(void);
void hex_dec(unsigned int value);
void main(void)
{                              
     
    //PORTC = 0x00;
    //DDRC  = 0x00;
                 
    DDRB|=0x20; 
    
    PORTD = 0x01;
    DDRD  = 0x01; 
    
    adc_init(); 
    spi_init();
    max_init(); 
 
    TCCR0 = 0x00;
    TCNT0 = 0x00;
    TIMSK  = 0x02;
 
    #asm("sei")
 
while (1)
      { 
        PORTD.0 = 1;                           //for LED
        adc_read_in();
        hex_dec(adc_display1);       
      }
}
void adc_read_in(void)
{
    adc_result1  = adc_read(0x61);                                  //adc connected to 1 so 61(0110 0001) see the adc header
    flag = 0;
    adc_display1 =(int) (adc_result1 * mul);                       //mul for bring (0-999) format
    hex_dec (adc_display1);
    
    delay_ms(100);
    
    adc_result2  = adc_read(0x62);
    flag = 1;
    adc_display2 = (int)(adc_result2 * mul);
    hex_dec (adc_display2);
  
    delay_ms(100);
}
void hex_dec(unsigned int value)
{ 
  if (value>100)
  {
    for (i=900;i>=100;i-=100)
    {
        if (value>=i)
        {
            value = (value - i);
            i = i/100;
            x=i;
            w = value/10;
            z = value%10;
            y = w%10;
            break;
        }
    }
  }
  else 
  {
        w = value/10;
        x = w/10;
        z = value%10;
        y = w%10;
        w = x/10;
        x = x%10;
  }
    
  if (flag == 0)
  {         
        max_data(6,(z + 0x30));
        delay_ms(10);
        max_data(5,(y+0x30));
        delay_ms(10);
        max_data(4,(x+0x30));
        delay_ms(10);
           
  }
  else if (flag == 1)
  {
        max_data(3,(z+0x30));
        delay_ms(10);
        max_data(2,(y+0x30));
        delay_ms(10);
        max_data(1,(x+0x30));
        delay_ms(10);
  }  
}
 
Last edited by a moderator: 

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void InitADC()
{
ADMUX=(1<<REFS0);                         // For Aref=AVcc;
ADCSRA = (1 << ADEN) | (1 << ADPS1) | (1 << ADPS0); //Rrescalar div factor =28 , 125KHz
//same as ADCSRA=0x83;
}
 
unsigned int ReadADC(unsigned char ch)
{
   
   ch=ch&0b00000111;
   ADMUX|=ch;
   ADCSRA|=(1<<ADSC);
   while(!(ADCSRA & (1<<ADIF)));
// mind the ; in the previous line
    ADCSRA|=(1<<ADIF);
 
   return(ADC);
}
 
void main()
{
float mul;
 unsigned int  adc_result;
mul=199.8;
float temp;
--------------------
---------------------- 
     InitADC();
-----------------------
  
   while(1)
   {
        adc_result=ReadADC(0); // Read Analog value from channel-0
    temp=adc_result*mul;
    adc_result=temp;
    //Display routine here
    Wait(); //enough delay
    adc_result=ReadADC(1); // Read Analog value from channel-1
    temp=adc_result*mul;
    adc_result=temp;
    //display routine here
    Wait();//enough delay
 
 
   }
}
 
Last edited:
i check my whole code . i got problem in ADC ,this code is not run in proteus software,properly .my point is ,ADC conversion is not finished.it means the code struggle at this line - while(!(ADCSRA & (1<<ADIF))); // Wait for AD interrupt flag

ADC program is
Code: 
void adc_init (void);                            //adc initialisation
unsigned int adc_read (unsigned char ch_select); //channel selection

void adc_init (void)
{
     ADCSRA  = (1<<ADEN) | (1<<ADPS1) | (1<<ADPS0); //125Khz
     ADMUX   = (1<<REFS0) | (1<<ADLAR);             //For Aref = AVcc 
}

unsigned int adc_read (unsigned char ch_select)
{
    unsigned int tenbit_value;
    unsigned char adc_low;
    
    ADCSRA  = (1<<ADEN) | (1<<ADPS1) | (1<<ADPS0); //125Khz    
    ADMUX |= ch_select; 
    ADCSRA = ADCSRA | (1<<ADSC);	            // Start ADC conversion
    while(!(ADCSRA & (1<<ADIF)));               // Wait for AD interrupt flag 
    ADCSRA |= (1<<ADIF);                        // Stop convertion 
    delay_ms(100);
    ADCSRA &= 0X00;    
    adc_low = ADCL;
    tenbit_value = (ADCH << 2 | adc_low>>6);     //make 10 bit value
    return tenbit_value;
}
 

selva murugesan said:
i check my whole code . i got problem in ADC ,this code is not run in proteus software,properly .my point is ,ADC conversion is not finished.it means the code struggle at this line - while(!(ADCSRA & (1<<ADIF))); // Wait for AD interrupt flag

ADC program is
Code: 
void adc_init (void);                            //adc initialisation
unsigned int adc_read (unsigned char ch_select); //channel selection

void adc_init (void)
{
     ADCSRA  = (1<<ADEN) | (1<<ADPS1) | (1<<ADPS0); //125Khz
     ADMUX   = (1<<REFS0) | (1<<ADLAR);             //For Aref = AVcc 
}

unsigned int adc_read (unsigned char ch_select)
{
    unsigned int tenbit_value;
    unsigned char adc_low;
    
    ADCSRA  = (1<<ADEN) | (1<<ADPS1) | (1<<ADPS0); //125Khz    
    ADMUX |= ch_select; 
    ADCSRA = ADCSRA | (1<<ADSC);	            // Start ADC conversion
    while(!(ADCSRA & (1<<ADIF)));               // Wait for AD interrupt flag 
    ADCSRA |= (1<<ADIF);                        // Stop convertion 
    delay_ms(100);
    ADCSRA &= 0X00;    
    adc_low = ADCL;
    tenbit_value = (ADCH << 2 | adc_low>>6);     //make 10 bit value
    return tenbit_value;
}
Click to expand...
Dear Selva,
I just have had like this problem with atmega8 ADC within proteus software, the firmware codes works over the PCB board but it does not work in proteus simulator;
 

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