A/D Conversion - Changing Resolution

[Bryan]

I am new to PICs and have been experimenting with the A/D convert function on my PIC18F1320. Here is the code I use to turn on an LED when the analog input voltage goes above a certain threshold:

#include <18F1320.h>
#fuses NOWDT,NOPROTECT,NOLVP,NOMCLR,INTRC_IO// CCPB0
#use delay(clock=20000000)

void main ()
{
setup_adc(ADC_CLOCK_INTERNAL);
setup_adc_ports(ALL_ANALOG);
set_adc_channel(1);
output_a(0x00);
output_b(0x00);
set_tris_a (0xFF);
set_tris_b (0x00);

while (1)
{
if(read_adc() >= 128)
{
output_high(PIN_B0);
}

else
{
output_low(PIN_B0);
}
}
}

Now, since I am comparing the read_adc() with 128, I expect this to be 1/8 of the reference voltage (I use 5V Vdd so I was expecting the LED to turn on at around 0.625V) since the resolution is supposed to be 10-bit or 1024 possible discrete levels. The strange thing is that it is acting like there is an 8-bit resolution since the LED turns on when I reach half of the reference voltage (Vdd is 5V and the LED comes on at 2.5V exactly) - I used a multimeter to make sure that my voltage readouts were correct. Anyone know how I can change a setting to make the A/D the full 10-bit that is possible with the PIC18? Any help would be appreciated!

[PCM programmer]

You could look in the manual or Help file in the read_adc() section.
But the answer is to add the line shown in bold below, immediately
after the #include line for your PIC.

#include <18F1320.h>
#device adc=10

[Bryan]

Thanks for the help, worked like a charm!

[UFAnders]

I have scoured the forum for reasons as to why I keep getting an 8-bit maximum value from my PIC 18F2520's ADC. I included the #device adc=10 statement directly after my chip's include file directive, and I have the read_adc() result flowing into an integer. I am viewing the value through HyperTerminal with fprintf() shooting out a zero-padded 4-digit result, but it still never goes higher than 255!

Any ideas? I'm using PCH 3.217.

Thank you!

[PCM programmer]

[UFAnders]

Haha, no way! You're absolutely correct - I declared this:

int ADCResult;

Then, just before I checked the forum again I tried:

long int ADCResult;

And ran it through:

fprintf(swrs232, "%04lu\r", ADCResult);

Works like a charm! Thanks for the super-quick reply, I imagined it would take weeks!