How to initialize ADC for PIC18f4620?

how to intitialize ADC in PIC18f4620?

what is adcon1,adcon2,vref?
i'm planning to make a temperature sensor using lm35.. pls help me.. where do i start..

sorry for my english..

You can find a project here: Tahmid's blog: Digital thermometer with LM35 and PIC18F452

There are many temperature sensor circuits here: Tahmid's blog

ADCON1 and ADCON2 are the control registers for the ADC. VREF is the reference voltage.

You can start reading about ADC here:
Using Analog to Digital Converter
www.gooligum.com.au/tutorials/midrange/PIC_Mid_A_13.pdf


Hope this helps.
Tahmid.

thank you very much..

when do i use ADCON1 or ADCON2 sir?

ADCON2 = 0x80; what is the meaning of "0x80"?

im using MikroC sir.. PIC18f4620.

0x80 means 80 in hexadecimal which is equal to 128 in decimal and 10000000 in binary.

I suggest you first download the datasheet for PIC 18F4620: ww1.microchip.com/downloads/en/DeviceDoc/39626b.pdf

Go to page 227 of the datasheet. There you have the ADCON2 register.
Writing 0x80 means you're commanding the ADC to display readings as right justified. Acquisition time is 0TAD, conversion clock is FOSC/2.

Go through the tutorials above and you should be able to understand everything clearly.

Hope this helps.
Tahmid.

sir can you please check what's wrong with my code?
the problem is i can't get the actual temperature.. for example The value of my LM35 is 31.0C in ISIS, but the output in virtual terminal is 31.2C..
27.0 c = 27.3 c
27.1 c = 27.3 c
27.2 c = 27.3 c
27.3 c = 27.3 c
27.4 c = 27.3 c
27.5 c = 27.8 c

void main() {
float temp,AdcTemp;
int IntegTemp1, IntegTemp2,DeciTemp;
ADCON2 = 0x82; // Configure analog inputs and Vref
TRISA = 0xFF; // PORTA is input
TRISB = 0x3F; // Pins RB7, RB6 are outputs
TRISD = 0; // PORTD is output
usart_init(9600);
delay_ms(500);


do {
AdcTemp= Adc_Read(2);
Temp = (AdcTemp*5000)/1023;
IntegTemp1 = (int) Temp*.01;
IntegTemp2 = (int) Temp*.1 - (IntegTemp1*10);
DeciTemp = (int) Temp*1 - (IntegTemp1*100+(IntegTemp2*10));

usart_write('T');
usart_write('E');
usart_write('M');
usart_write('P');
usart_write('=');
usart_write(IntegTemp1+48);
usart_write(IntegTemp2+48);
usart_write('.');
usart_write(DeciTemp+48);
usart_write(' ');
usart_write('C');
usart_write(13);
usart_write(10);
delay_ms(400);
} while(1);
}

the problem actually is the "DeciTemp". Please help sir.

This is because, LM35 provides an output with a guaranteed accuracy of 0.5°C. Expecting any better accuracy is useless. So, your reading has to vary by 0.5°C steps, not 0.1°C steps like your program does.

Hope this helps.
Tahmid.

so if i want better accuracy, i have to change my sensor(LM35)?
can you suggest other sensor for temperature sir...?

Yes, you need to change the sensor. I don't know of any sensor IC that accurate. However, you could see if you can find a suitable thermistor. There are some quite accurate ones.

Tnx sir.