pic16f877a ADC source code for lm35

[Tys0n]

Hi

I'm using CCS PCWHD compiler,
What changeS should I make so as to keep my PIC ADC : +Vref = 1.2v and -Vref = ground
(which I kept using potential divider arrangement)

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Transmitting side code
#include <16F877A.h>
#device *= 16
#device adc=8
#fuses HS, NOWDT, NOPROTECT,
NOLVP, PUT
#fuses NOBROWNOUT, CPD,
NODEBUG, NOWRT
#use delay(clock=10MHz)
#use rs232(baud=1200, xmit=PIN_
C6, bits=8, parity=N)
#include <lcd.c>
void main()
{
byte s=0;
lcd_init();
lcd_putc("\f");
setup_adc_ports(adc_clock_internal);
setup_adc(AN0);
set_adc_channel(0);
while(true)
{
read_adc(adc_start_only);
while(!adc_done());
s = read_adc(adc_read_only);
lcd_gotoxy(1,1);
printf(lcd_putc, "\fTx Data = %u" s);
putc(s);
delay_ms(100);
}
}

 

[jayanth.devarayanadurga]

See here. https://www.edaboard.com/threads/282844/

I have posted a working project there.

 

[Tys0n]

I just want to know how to configure PIC adc for given reference voltage in that source code.....

setup_adc(???);

 

[jayanth.devarayanadurga]

Setup_adc() right. I have used 2V Vref+ and 0V Vref-.

 

[Tys0n]

But its not helping, in proteus simulation it is showing 255 equivalent to 5V. I just want my range to be btwn 0 to 1.2V for ADC.

 

[jayanth.devarayanadurga]

LM35 max output is 1.5 V, So your Vref+ should be around 1.8V. Post your project files. Maybe you used an int8 variable to hold the value of adc read. You need a 16bit int or float for that.

I found the problem.

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Code C - [expand]
1
#device adc=8

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is wrong. You have to use

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Code C - [expand]
1
#device adc=10

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as PIC16F877A's adc is 10 bit.

If adc=8 is used then 8bit is considered and 2^8 is 256 i.e., 0-255, so, you are getting 255.

 

[Tys0n]

Actualy I used byte since my I'm doing 8-bit data transmission later so can't use 10bit adc.... So as to increase the 8bit resolution, I want my ADC conversion range to be just 0-1.2 V
i.e. 1.2v should be equivalent to 255

 

[jayanth.devarayanadurga]

PIC16F877A ADC is 10 bit. If you use Vref+ as 1.2 V then with 10 bit adc you get 1023 raw adc value for 1.2 V. I don't know how to make it work as 8 bit adc.

 

[Tys0n]

8bit ADC is working fine, but by this source code its taking 5V as reference even aftr applying 1.2V to Vref+ i.e pin 5
How to configure ADCON in CCS code to make PIC to take into account the reference voltage?

 

[jayanth.devarayanadurga]

Post your setup_adc() statement you used in your code. If possible post 16f877a.h file included in your code.

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Code C - [expand]
1
2
setup_adc_ports(AN0_AN1_AN2_AN4_AN5_AN6_AN7_VSS_VREF);
setup_comparator(NC_NC_NC_NC);

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