reading adc from atmega8

[gavi prakash]

Hi to all,

I am reading adc values using atmega8 controller, the problem is it is always reading 1023 if im changing valus through pot. the code is lik below

 

 #include <avr/io.h>

#include <util/delay.h>

 #include "lcd.h"

  

void InitADC()

{

ADMUX=(1<<REFS0);                         // For Aref=AVcc;

ADCSRA=(1<<ADEN)|(1<<ADPS2)|(1<<ADPS1)|(1<<ADPS0); //Rrescalar div factor =128

}

 

uint16_t ReadADC(uint8_t ch)

{

   //Select ADC Channel ch must be 0-7

   ch=ch&0b00000111;

   ADMUX|=ch;

   

 ADCSRA |= (1<<ADSC);

 

    // wait for conversion to complete

    // ADSC becomes '0' again

    // till then, run loop continuously

    while(ADCSRA & (1<<ADSC));

 

    return (ADC);

}

 

void Wait()

{

   uint8_t i;

   for(i=0;i<20;i++)

      _delay_loop_2(0);

}

 

void main()

{

   uint16_t adc_result;

   char int_buffer[10];

DDRB=0xFF;

DDRC=0x00;

DDRD=0xFF;

   //Initialize ADC

   InitADC();

init_lcd();

while(1)

   {

      adc_result=ReadADC(0);           // Read Analog value from channel-0

       itoa(adc_result, int_buffer, 10);

 

lcd_str(int_buffer);

lcd_cmd(0x01);

lcd_cmd(0x03);

      Wait();

   }

}

….

 

Please help me i hav connect pot to adc(0) channel if any varying pot then also it is taking high(1023) value only .

 

[gavi prakash]

please anyone tell me the solution

[Arjun Singh]

Hello friend

As i come to know there is problem in your "uint16_t ReadADC(uint8_t ch)" function

 " while(ADCSRA & (1<<ADSC));" this statement is wrong. As adsc is to start conversion.

You need to write-

while(!(ADCSRA & (1<<ADIF))); // waiting for ADIF, conversion complete

ADCSRA|=(1<<ADIF); // clearing of ADIF, it is done by writing 1 to it

 

After this modification your code will properly run.

 

Any doubt, feel free to ask

[Author]

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