how to select acquisition time in A/D?

[FvM]

I guess, you expect highbyte to be copied to the upper byte of full_value?

full_value = ((high_byte<<8)|low_byte);

But according to C language rules it isn't. high_byte<<8 is still an int8 value. (int16)high_byte<<8 will do.
With CCS C, you'll possibly want to use the built-in make16() function for this purpose, or even more comfortable, use the respective ADC functions.

 

[hemnath]

yes when i tried using inbuilt functions, it works perfectly. for 0V, it shows 0 in LCD and for 5V it shows 1023 in LCD display.

Now the problem is solved. i have changed the line

unsigned int8 low_byte,high_byte;

to

unsigned int16 low_byte,high_byte;

.Now simulated in proteus, it works good. Tomorrow ill run it in hardware and check. thank you so much tahmid and jayanth for your help ...

 

[hemnath]

I tested with real hardware. It works. but the problem is, display value is haunting. i rotated the pot to some value and kept silent.
for eg. if lcd value is 910. and it rolling over from 890 to 920. why is it so?

 

[jayanth.devarayanadurga]

Post your code.

 

[hemnath]

It's good in proteus. But in hardware, value in LCD fluctuates.

#include "18F2520.h"
#include "f2520_regs.h"
#fuses INTRC_IO					// Internal clock
#use delay(clock=4000000) 		// 4MHZ

#define RS PIN_A2  	// LCD RS pin connected to uC PIN_A2
#define EN PIN_A1	// LCD EN pin connected to uC PIN_A1

void lcd_init();
void lcd_cmd(unsigned char);
void lcd_data(unsigned char);

unsigned int16 low_byte,high_byte;
unsigned int16 full_value; 

void main()
{
lcd_init(); 				// lcd initialization
TRISA  = 0b00100000;		// RA5 -input, rest as output
ADCON0 = 0b00010000;		// analog channel 4, A/D on
ADCON1 = 0b00001010;		// ref volt. VSS and VDD. AN4 to AN0 as analog
//ADCON2 = 0b10110100;		// Right justified, 16 TAD, 1/4Tosc
//ADCON2 = 0b10110101;       //FOSC/16
 ADCON2 = 0b10111100;
ADON = 1;
while(1)
{
delay_us(10);   
GO = 1;  					// to start conversion	
while(GO==1);				// wait for bit to be cleared
low_byte = ADRESL;			 
high_byte = ADRESH;
full_value = ((high_byte<<8)|low_byte);
lcd_cmd(0x80);
printf(lcd_data,"%4lu",full_value);
delay_ms(100);
}
}

void lcd_init()
{
lcd_cmd(0x30);      // Configure the LCD in 8-bit mode, 1 line and 5x7 font
lcd_cmd(0x0c);      // display on and cursor off
lcd_cmd(0x01);      // clear display screen
lcd_cmd(0x06);      // increment cursor
lcd_cmd(0x80);      // set cursor to 1st line
}

void lcd_cmd(unsigned char c)
{
output_b(c);
output_low(RS);
output_high(EN);
delay_ms(15);
output_low(EN);
}

void lcd_data(unsigned char z)
{
output_b(z);
output_high(RS);
output_high(EN);
delay_ms(15);
output_low(EN);
}

 

[jayanth.devarayanadurga]

Then the problem is with your hardware. Post your circuit.

 

[hemnath]

This is the circuit, i used inbuilt functions. It works good. But when using the registers in the program, it makes some problem

 

[Tahmid]

It's good in proteus. But in hardware, value in LCD fluctuates.

If the fluctuation is within a small range, using an RC filter should solve this issue and help stabilize it.

Go through the TIPS AND TRICKS section here: https://www.edaboard.com/blog/1574/

Hope this helps.
Tahmid.

 

[jayanth.devarayanadurga]

Post the code which uses registers.