ADC problem on 16F877

[Onur]

I wrote a adc program.. but cant understand some point...

I used 2 acd input.. first input for lm35
second inpur for 0 to 5v range ...

pic can measure lm35 out...I haven't got any problem abot this..

I connected other port potantiometer(pot)
pots wire connected +,- and adc input..

if I turn pot middle I see 0
it can measure 0v to 2.55 volt
an I continue turning I see 0 to 255

it can measure 0 to 255
I must measure 0V to 5v
it range 0-255
How to do it this?
Thank you

(I connected RA2 to gnd and RA3 to 5v)
#INCLUDE <16F877.h>
#DEVICE ADC=10
#use delay(clock=20000000)
#FUSES HS,NOWDT,NOPROTECT,NOLVP,noPUT, NOBROWNOUT
#use rs232(baud=9600, xmit=PIN_E0, rcv=PIN_E1)

long number;
long number2;

set_tris_A(1);
void main(){


setup_port_a(RA0_RA1_ANALOG_RA3_RA2_REF);

setup_adc( ADC_CLOCK_DIV_32 );
SETUP_ADC(ADC_CLOCK_INTERNAL);



do{
set_adc_channel( 1 );
delay_ms(200);
number = Read_ADC();
delay_ms(200);

putc(number);

set_adc_channel( 0 );
delay_ms(200);
number2 = Read_ADC();
delay_ms(200);

putc(number2);


} while(true);

}

[asjad]

I think the problem is with your ADC reference voltage.

OR

I do not think the PIC ADC can measure upto +5v, if the supply to the PIC
is +5v


Hope this helps!!
_________________
Best Regards

[Neutone]

[Guest]

not sure what your looking for help on?

but with an 8bit a/d you get 255 levels
so you divide 5v by 255 = 20mv per level

so when it dsys 1 it is reading 20mv,
10 = 200mv
100 = 2v
.
....
......
.......
255 = 5v

[Onur]

but when I turn pot I can read in the middle of the pot 0-255 and I contunue turning it starts 0 t0 255

[Guest]