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steppermotor
Joined: 24 Oct 2010
Posts: 10
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| PIC 16F877A LCD with ADC |
 Posted: Thu Oct 28, 2010 7:33 pm |
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I'm new to the world of PIC. I've got my LCD working, but I'm trying to display the voltage I that is read in by the PICs ADC port. I'm using the PIC 16F877A, here is sections of my code. However it keeps displaying 8, even when I have it connected to 5 Volts or ground. Any idea what's wrong with my code, that is does not measure the correct voltage.
| Code: |
char print_lcd(char s[])
{
delay_ms(1000);
lcd_putc('\f');
delay_ms(250);
output_high(pin_b0);
delay_ms(250);
printf(lcd_putc,"LCD Works");
delay_ms(5000);
lcd_gotoxy(0x1,2);
lcd_putc(s);
return s;
}
void measure_voltage()
{
char txt[20];
int16 voltage, adc_value;
while(true){
set_adc_channel(0);//set the pic to read from AN0
delay_us(20)
adc_value = read_adc();
voltage = adc_value*(5/1023);
sprintf(txt, "%i\0", (int)voltage);
print_lcd(txt);
}
}
void main()
{
char txt[20] = "yes";
setup_adc(ADC_CLOCK_DIV_8);
setup_adc_ports(ALL_ANALOG);
setup_psp(PSP_DISABLED);
setup_spi(SPI_SS_DISABLED);
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);
output_low(pin_b0);
lcd_init();
print_lcd(txt);
measure_voltage();
} |
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vinniewryan
Joined: 29 Jul 2009
Posts: 154
Location: at work
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| Posted: Thu Oct 28, 2010 8:19 pm |
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Well in the line "voltage = adc_value*(5/1023);", you're multiplying "voltage" by .004, and if your ADC value is anywhere between 1875 and 2124, then your outcome would always be 8 because the PIC would round the number to the nearest integer. Try removing the "(5/1023)" and report the result.
I see no appearent mistakes in your code, so you may also want to post the rest of the code as well.
You can also try writing a simple code that only tests the ADC port, something like:
| Code: |
#include '16f677.h'
#use_delay(clock=xxxxxxx)
#use adc=10
#define//
int16 voltage=0;
void main()
{
while(1)
{
setup_adc(ALL_ANALOG)
set_adc_channel(0);
delay_us(20);
voltage=read_adc;
printf('%i', voltage);
}
}
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This is just an example, not a working code.
_________________
Vinnie Ryan |
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steppermotor
Joined: 24 Oct 2010
Posts: 10
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| Re:LCD W ADC |
| Posted: Thu Oct 28, 2010 8:33 pm |
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Thanks, Vinnie for your reply, I made the following modifications. The output is just 000000, even when I have plugged the RA0 to 5 V.
| Code: |
void measure_voltage()
{
//char txt[20];
int adc_value;
int16 voltage;
//float voltage;
output_high(pin_b0);
delay_ms(250);
printf(lcd_putc,"LCD Works");
while(1)
{
set_adc_channel(0);
delay_us(20);
voltage=read_adc();
printf(lcd_putc,"%lu",voltage);
}
}
void main()
{
setup_adc(ADC_CLOCK_INTERNAL);
setup_adc_ports(ALL_ANALOG);
setup_psp(PSP_DISABLED);
setup_spi(SPI_SS_DISABLED);
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(TRUE);
output_low(pin_b0);
lcd_init();
//print_lcd(txt);
measure_voltage();
} |
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steppermotor
Joined: 24 Oct 2010
Posts: 10
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| Got it working |
| Posted: Thu Oct 28, 2010 8:43 pm |
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Thanks, but I got it working.
I modified to the following:
| Code: |
while(1)
{
set_adc_channel(0);
delay_us(20);
voltage=read_adc();
printf(lcd_putc,"%u",voltage);
} |
and changed setup_adc(ADC_CLOCK_DIV_32);
from setup_adc(ADC_CLOCK_INTERNAL);
Thanks |
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steppermotor
Joined: 24 Oct 2010
Posts: 10
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| One more problem |
| Posted: Thu Oct 28, 2010 9:12 pm |
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When I have a 5V input on my PIC 16F877A ADC AN0 Port is outputs:
1023 on the LCD which I know is the correct value, but when I attempt to multiply by 5/1023 and this does not gives me a result of zero. Perhaps I'm using the wrong int/float/lu. Any suggestions?
| Code: |
void measure_voltage()
{
int16 voltage;
int16 con_voltage;
float con_voltage2;
//float voltage;
output_high(pin_b0);
delay_ms(250);
printf(lcd_putc,"LCD Works");
//while(1)
// {
set_adc_channel(0);
delay_us(20);
voltage=read_adc();
printf(lcd_putc,"%lu\n",voltage); // This displays 1023 which is correct for 5 VDC
con_voltage = (int)voltage * (5/1023);
printf(lcd_putc,"%lu",con_voltage); //outputs 0
delay_ms(20);
con_voltage2 = (int)voltage * (5/1023);
delay_ms(20);
printf(lcd_putc," %lf",con_voltage2); //outputs 0
// }
} |
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steppermotor
Joined: 24 Oct 2010
Posts: 10
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| Got it again |
| Posted: Thu Oct 28, 2010 9:41 pm |
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I changed:
| Code: |
while(1)
{
set_adc_channel(0);
delay_us(20);
voltage=read_adc();
con_voltage2 = voltage * (5.0/1023.0);
delay_ms(20);
printf(lcd_putc,"\n%lf",con_voltage2);
}
} |
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