Need Help: AVR Analog-to-Digital Converter

[Don_dody]

I use the following part of code to read the ADC value:

 unsigned int read_adc(unsigned char adc_input)
 {
    ADMUX=adc_input | (ADC_VREF_TYPE & 0xff);
    delay_us(10);
    ADCSRA|=0x40;
    while ((ADCSRA & 0x10)==0);
    ADCSRA|=0x10;
    return ADCW;
 }


    while (1)
      {
        A1=read_adc(0);
        lcd_gotoxy(0,0);
        sprintf(buf,"L1:%d%d%d%d",A1/1000,(A1%1000)/100,(A1%1000%100)/10,A1%1000%100%10);
        lcd_puts(buf);
       }

The value that I see in the 16x2 LCD is always changing (very very fast). Is there any way to overcome this so that ADC value will be updated slowly, at least I can see it??

 

[alexxx]

There are two methods for that. You could read ADC at a slower rate, or you could update the result on LCD at a slower rate. I have heard people using both techniques. If you ask me, I prefer the second approach. The ADC result could be used from other parts of the program as well, like the detection of a low AC level for example, if we assume that the ADC is used to read mains voltage. Since you are not keeping a timebase in this sample program, you could experiment with cycles delays like this:

#define _VISUALIZATION_CYCLES    100000ul
unsigned long cnt=0;

while (1)
{
  A1=read_adc(0);

  cnt++;
  if (cnt >= _VISUALIZATION_CYCLES)
  {
    cnt = 0;
    lcd_gotoxy(0,0);
    sprintf(buf,"L1:%d%d%d%d",A1/1000,(A1%1000)/100,(A1%1000%100)/10,A1%1000%100%10);
    lcd_puts(buf);
  }
}

You could then experiment with _VISUALIZATION_CYCLES value, to achieve the result that is most convenient for you.

 

[wp100]

Hi,

Add in a delay of say ms(250) after each ADC result.

You may find the lsb of the result fluctuate a lot, even if the input is stable; often over come by running a x16 averaging routine

 

[Don_dody]

Thanks for helping.
I need to use this ADC value for another program and it should be accurate. If it changing too much, I bet I'll get more problem.