problem with adc conversion code in atmega 16

[Shivam]

My adc conversion code is as follows…I am giving the analog i/p at pin 39 of atmega16….the adc is used in 10 bit resolution and lcd is in 4 bit mode…I have tested the code on the lcd…It shows me 1023 as the o/p….but the value doesnt change even if i change the analog i/p to pin 39.I think there might be some problems with my adc initialization….Can u please help me?

 

 

 

 

//ICC-AVR application builder : 7/22/2011 8:16:48 PM
// Target : M16
// Crystal: 16.000Mhz

#include <iom16v.h>
#include <macros.h>
#include <lcd.h>

void port_init(void)
{
 PORTA = 0x00;
 DDRA  = 0xFD;
 PORTB = 0x00;
 DDRB  = 0x00;
 PORTC = 0x00; //m103 output only
 DDRC  = 0xFF;
 PORTD = 0x00;
 DDRD  = 0x00;
}

//ADC initialize
// Conversion time: 52uS
void adc_init(void)
{
 ADCSR = 0x00; //disable adc
 ADMUX = 0x21; //select adc input 1
 ACSR  = 0x80;
 ADCSR = 0x87;
 ADCSRA|=(0x40);
}

unsigned int read_adc(unsigned char ADC_channel_no)
{
  unsigned int j=0,val;
unsigned char i;
  ADCH=0x00;
  i=ADC_channel_no&0x0F;
  ADMUX=i|0x21;
  ADCSR|=0x40;
  for(j=1;j<1023;j++);
   val=(ADCH*4)+(ADCL/64);
    return(val);
}

void DELAY1(unsigned int dela)
{
    
    int i,k;
    for(k=0;k<dela;k++)
    {

        for(i=0;i<50000;i++)
        {}
        
            
    }

}
 
 

 

//call this routine to initialize all peripherals
void init_devices(void)
{
 //stop errant interrupts until set up
 CLI(); //disable all interrupts
 port_init();
 adc_init();

// MCUCR = 0x00;
// GICR  = 0x00;
// TIMSK = 0x00; //timer interrupt sources
 SEI(); //re-enable interrupts
 //all peripherals are now initialized
}

//
void main(void)
{
 unsigned int i;
 init_devices();
 LCD_INIT();

  while(1)
  {       
           i=read_adc(1);
           LCD_WRITE(“vtg=”,4);
           LCD_NO(i);
           DELAY1(5000);
  }    
}

[GANEEV SINGH]

Hi Shivam

The code thing seems to be fine. One reason could be that you might have not given a proper voltage to Aref pin (pin 32). It is used to provide a reference voltage for A to D conversions, generally we connect this pin to +5 V. 

This might work

[Ashutosh Bhatt]

connect AVCC pin and AREF pins of ATMega16 micro controller to +5 V

try to check if analog voltage at pin 39 actually varies or not. what kind of input you have given to pin 39?

[Author]

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