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ahmad-al3omar
Joined: 25 May 2007
Posts: 16
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| multiple ADC problem |
 Posted: Wed May 14, 2008 3:57 pm |
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hello all;
i am working on
PIC16F877A
CRYSTAL 4MHz
i am using a program that read from two potentiometers to the channel (0) and channel (1). when play the code on the simulation every thing is ok.
but when we apply it on the circuit there is a problem which is the value read from the first channel when we change the pot. meter value changes and also the read value from the second channel changes why i don't know, and the read value does not print the maximum value which is +5 volts.
my code below and please help me!!
| Code: |
#include<16f877a.h>
#fuses noprotect,nowdt,xt
#use delay(clock=4000000)
#include<lcd.c>
#define A pin_c6
#define B pin_c7
#define C pin_c5
int tim,motor,con,timm;
int16 freq,count;
float dig_alc,ang_alc,ang_temp,dig_temp;
int over();
main()
{
lcd_init();
setup_adc_ports(all_analog);
setup_adc(adc_clock_internal);
output_low(pin_b3);
output_low(pin_b4);
output_low(pin_b5);
output_low(pin_b6);
output_low(pin_b2);
output_low(pin_b1);
con=1;
while(1)
{
set_adc_channel(0);
dig_alc=read_adc();
ang_alc=dig_alc/510;
delay_us(50);
set_adc_channel(1);
dig_temp=read_adc();
ang_temp=dig_temp/51;
delay_us(50);
motor = input(pin_e0);
lcd_gotoxy(1,1);
printf(lcd_putc," alcohol = %f%% \n t=%f ",ang_alc,ang_temp);
if(ang_alc>0.25 && con==1)
{
con=0;
motor = input(pin_c1);
over();
}
if(ang_temp>2 && con==1)
{
con=0;
motor = input(pin_c1);
over();
}
if(freq > 200 && con==1)
{
con=0;
motor = input(pin_c1);
over();
}
}
}
over()
{
motor = input(pin_c1);
output_high(pin_b1);
enable_interrupts(INT_RTCC);
output_high(pin_c5);
if(motor)
{
output_high(pin_b1);
delay_ms(1000);
output_low(pin_b1);
delay_ms(1500);
output_high(pin_b1);
delay_ms(1000);
output_low(pin_b1);
delay_ms(2500);
output_high(pin_b1);
delay_ms(1000);
output_low(pin_b1);
delay_ms(3500);
output_high(pin_b1);
delay_ms(1000);
output_low(pin_b1);
delay_ms(4500);
output_high(pin_b1);
delay_ms(1000);
output_low(pin_b1);
delay_ms(5500);
output_high(pin_b1);
delay_ms(1000);
output_low(pin_b1);
delay_ms(6500);
output_high(pin_b1);
}
output_low(pin_b3);
output_low(pin_b4);
output_low(pin_b5);
output_low(pin_b6);
output_low(pin_b2);
} |
_________________
A.T.N |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Wed May 14, 2008 4:27 pm |
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The compiler defaults to using 8-bit mode for the A/D result.
You have to add the line shown in bold below to get a 10-bit result.
Also, you should add the NOLVP fuse for safety.
| Quote: | #include<16f877a.h>
#device adc=10
#fuses noprotect,nowdt,xt,NOLVP
#use delay(clock=4000000)
#include<lcd.c> |
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n-squared
Joined: 03 Oct 2006
Posts: 99
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| Posted: Wed May 14, 2008 9:58 pm |
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I found out that ADC readings work much better if you put a short delay between channel selection and the actual read:
| Code: |
set_adc_channel(3);
delay_us(10);
x = read_adc();
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_________________
Every solution has a problem. |
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