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PIC16F877-A ADC random values.

 
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meme



Joined: 29 Jun 2005
Posts: 13

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PIC16F877-A ADC random values.
PostPosted: Sun Aug 07, 2005 5:15 am     Reply with quote
I am using pic16f877A and on pin A1 I have a analog input. the code is:


Code:
#include "C:\Program Files\PICC\Termometru\termometru1.h"
#include <LCD.C>
#include <stdlib.h>

void main()
{

unsigned long val;
   setup_adc_ports(AN0_AN1_VSS_VREF);
   setup_adc(ADC_CLOCK_INTERNAL);
   setup_psp(PSP_DISABLED);
   set_adc_channel(1);

   setup_spi(FALSE);
   setup_timer_0(RTCC_INTERNAL|RTCC_DIV_1);
   setup_timer_1(T1_DISABLED);
   setup_timer_2(T2_DISABLED,0,1);
   setup_comparator(NC_NC_NC_NC);
   setup_vref(FALSE);
   lcd_init();

delay_ms(200);
lcd_putc("Termometru...\n   Asteptati...");
while(1){
   delay_ms(2000);
   val = read_adc();
   delay_ms(100);
   printf(lcd_putc,"\fADC Val: %ld",val);
  }

}


Termometru1.h is:

Code:
#include <16F877A.h>
#device adc=10
#use delay(clock=4000000)
#fuses NOWDT,XT, PUT, NOPROTECT, NODEBUG, NOBROWNOUT, NOLVP, NOCPD, NOWRT



on pin A1 I connected a 50K variable resistor (connected between the power supply 5V and ground).

Even if I don't modify the resistor I get strange results on my LCD: sometimes I get 1023 (the maximum value) sometimes I get 0. Also i get other values: 512, 640, 1 etc without modifying the resistor.
Any Ideas ?
thanks
Humberto



Joined: 08 Sep 2003
Posts: 1215
Location: Buenos Aires, La Reina del Plata

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PostPosted: Sun Aug 07, 2005 7:42 am     Reply with quote
setup_adc_ports(AN0_AN1_VSS_VREF);

Is expecting the Vrefh in PIN_A3. Are you getting the Vref HIGH to this pin ?

Check the possible constants used in SETUP_ADC_PORTS() in the 16F877A.H file.

Best wishes,

Humberto
meme



Joined: 29 Jun 2005
Posts: 13

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PostPosted: Sun Aug 07, 2005 8:08 am     Reply with quote
that was it. thanks !
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