unexpected A/D converted values.

[thivanka321]

i wrote a programme in ccs c, to display A/D conversion values in hyperterminal.
i used pic 18f452. what i'm really converting is anlogue values taken from accelerometer.
but there is a unexpected problem. that is even without setting accelerometer to the A PORT of the pic, hyperterminal displays A/D converted values.
i checked the controler board whether there is a signals to A port. but there is not.
i;m sure pic controller board is ok. it works with other programmes ,well.

what is the reason for that? any problem with programme or what?
reply me soon.

#include "G:\ccsfiles\project2.h"


void main()
{
 float value;

   setup_adc_ports(AN0_AN1_AN2_AN3_AN4);
   setup_adc(ADC_OFF);
   setup_psp(PSP_DISABLED);
   setup_spi(FALSE);
   setup_wdt(WDT_OFF);
   setup_timer_0(RTCC_INTERNAL);
   setup_timer_1(T1_DISABLED);
   setup_timer_2(T2_DISABLED,0,1);
   setup_oscillator(False);

   // TODO: USER CODE!!
  setup_adc(ADC_CLOCK_DIV_8);
  // setup_uart(19200);
   set_tris_b(255);
  output_D(0);

     while(1)
   {
       set_adc_channel( 2 );
      delay_us(20);
     value = read_adc();
       
    
     printf("x = %8.3f\n\r",value);
      set_adc_channel( 1 );
      delay_us(20);
    value = read_adc();
     printf("y = %8.3f\n\r",value);

      set_adc_channel( 0 );
      delay_us(20);
      value = read_adc();
     printf("z = %8.3f\n\r",value);
     output_D(255);
}

}

 

[FvM]

even without setting accelerometer to the A PORT of the pic, hyperterminal displays A/D converted values

It can hardly do different, I think. The ADC doesn't care what's connected to it's input, it's simply measuring voltages. To check correct
ADC operation, you may want to connect a variable voltage source (e.g. a potentiometer connected to the 5V supply) to
the ADC and observe the readings.

 

[numa]

I never worked with CCS C, but I believe the return value from read_adc() function should be an int rather than float. Try declaring variable value as int instead of float. And try averaging 2-3 samples to get the final value rather than using a single sample. This is not very important but may help you a bit if your hardware sits in a noisy environment.