ADC to LCD doesn't convert over 2.5v???

harsha3842 · Jul 5, 2013

i'm using pic18f4520 and coding from mplab c18 using C
the below code works absolutely fine
only prob is it doesn't convert values above 2.5v i.e 511
wats the error????????

Rich (BB code):

#include <p18cxxx.h>
#include <adc.h>
#include <stdlib.h>
#include <delays.h>
#include <stdio.h>

#define rel_staff PORTA
#define  E LATDbits.LATD7
#define  RS  LATDbits.LATD6
#define lcdport LATB
#define _XTAL_FREQ 20000000

#pragma config WDT=OFF, LVP=OFF, DEBUG=ON, MCLRE = OFF
#pragma config OSC=HS

int adc_out=0;
float adc_value=0;
unsigned char voltage[5];

void ftoa(float, char *);
void lcdcomm(unsigned char);
void lcddata(unsigned char);
void lcdout(unsigned char);
void lcdmsg(const rom char *);
void lcdstr(unsigned char *);
void lcdblank(void);
void lcdblink(void);
void lcdclear(void);
void lcdinit(void);

void main (void)
{
    TRISC = 0x00;
    TRISA = 0x0F;
    TRISB = 0x00;
    TRISD = 0x00;
    lcdinit();
    lcdcomm(0x80);
    lcdmsg("RELISYS");
    lcdcomm(0xC0);
    lcdmsg("TECHNOLOGIES");
    Delay10KTCYx(1000);
    Delay10KTCYx(1000);
    lcdblank();
    lcdcomm(0x80);
    lcdmsg("Channel 1:");
    lcdcomm(0x8F);
    lcdmsg("V");
    lcdcomm(0xC0);
    lcdmsg("Channel 2:");
    lcdcomm(0xCF);
    lcdmsg("V");
    OpenADC(ADC_FOSC_2 &
        ADC_RIGHT_JUST &
        ADC_2_TAD,
        ADC_CH0 &
        ADC_INT_OFF &
        ADC_VREFPLUS_VDD &
        ADC_VREFMINUS_VSS,ADC_2ANA);
    do
    {
        SetChanADC (ADC_CH1);
        Delay10KTCYx(10);
        ConvertADC();
        while(BusyADC());
        adc_out=ReadADC();
        adc_value=(adc_out*5.0)/1024;
        ftoa(adc_value,voltage);
        lcdcomm(0x8A);
        lcdstr(voltage);

        SetChanADC (ADC_CH2);
        Delay10KTCYx(10);
        ConvertADC();
        while(BusyADC());
        adc_out=ReadADC();
        adc_value=(adc_out*5.0)/1024;
        ftoa(adc_value,voltage);
        lcdcomm(0xCA);
        lcdstr(voltage);
        Delay10KTCYx(1000);
        lcdclear();
    }
    while(1);
}

void lcdmsg(const rom char *Message)
{
    const rom char *Pos = Message;
    while(*Pos!=0)
        lcddata(*Pos++);
}
void lcdstr(unsigned char *str)
{
    int i=0;
    while(str!='\0')
    {
        lcddata(str);
        i++;
    }
}

void lcdcomm(unsigned char i)
{
    RS =0;
    lcdout(i);
    Delay1KTCYx(2);
}
 
void lcddata(unsigned char i)
{
    RS =1;
    lcdout(i);
    Delay1KTCYx(2);
}
 
void lcdout(unsigned char dat)
{
    lcdport = dat;
    E = 1;
    Delay1TCY();
    E = 0;
}
 
void lcdinit(void)
{
    lcdport=0x00; 
    Delay1KTCYx(40);
    lcdout(0x30);
    Delay1KTCYx(15);
    lcdout(0x20);
    Delay1KTCYx(15);
 
    lcdcomm(0x38);
    lcdcomm(0x0C);
    lcdcomm(0x01);
    lcdcomm(0x06);
    lcdcomm(0x80);
}

void lcdblank(void)
{
    lcdcomm(0x80);
    lcdmsg("                ");
    lcdcomm(0xC0);
    lcdmsg("                ");
}

void lcdclear(void)
{
    lcdcomm(0x8A);
    lcdmsg("     ");
    lcdcomm(0xCA);
    lcdmsg("     ");
}

void lcdblink(void)
{
    Delay10KTCYx(200);
    lcdcomm(0x89);
    lcdmsg("       ");
    Delay10KTCYx(200);
}

void ftoa(float value, char *string) 
 { 
     if (value < 0) { 
         *string++ = '-'; 
         value = -value; 
     } 
     sprintf(string, (const far rom char *) "%lu.%03u", 
                     (long) value, 
                     (int) ((value - (long) value) * 1000. + 0.5)); 
 }

donpetru · Jul 5, 2013

Do not show or do not convert higher values of 2.56V because the ADC reference voltage is 2.56V. Show the circuit diagram to see if the reference is 2.56V or not.
Then, what is the maximum voltage you want to measure?

LATER EDIT: In your software try to use instead:

int adc_out = 0;

this:

unsigned int adc_out = 0;

tshuck · Jul 5, 2013

It would appear your are assuming a 5V reference, which is attached to your Vdd, now, the question becomes, are you actually using a 5V supply?

Try debugging the code and ensure the result returned from the ADC is as expected...

I would urge you to not use so many compiler-specific operations - the C18 compiler is on its way to obsolescence, and your code would need to be refactored, if ever you had to rebuild this code in years to come. This is, of course, advice, and you may our may not agree, but that is my two cents on the matter...

harsha3842 · Jul 5, 2013

Isn't the pic18f range from 0 to 5v?
Yes im giving an external supply
The cinversion works absolitely gine till 2.5v and it displays 2.495v on my lcd
But any value over 2.5 I don get any variation

THE_RB · Jul 6, 2013

It could be your ReadADC() function being faulty, returning only 9 of the 10 ADC bits.

A good method is to display the 10bit ADC value (adc_out), for debugging.

harsha3842 · Jul 6, 2013

the 10 bit ADC value(adc_out) gives max of 511 only

LDC3 · Jul 6, 2013

harsha3842 said:
the 10 bit ADC value(adc_out) gives max of 511 only

A 1 in the 10th bit (0x200) gives a value of 512, so 0x3FF is 1023.

harsha3842 · Jul 6, 2013

my prob is why am i not getting that 1 in the 10th place???
wat is stopping the value from reaching there???

tshuck · Jul 6, 2013

harsha3842 said:
my prob is why am i not getting that 1 in the 10th place???
wat is stopping the value from reaching there???

...this is what we are trying to ascertain. Have you tried to debug your code yet?

harsha3842 · Jul 6, 2013

yes everything seems ok
not able to find out that single bit
any config errors?

tshuck · Jul 6, 2013

harsha3842 said:
yes everything seems ok
not able to find out that single bit
any config errors?

So, what does your read function return? There is a point that your program is misinterpreting the value, single-step your code and check the value at each break...

harsha3842 · Jul 6, 2013

the code works now
thank you all for the assistance

Rich (BB code):

#include <p18cxxx.h> 
 #include <adc.h> 
 #include <stdlib.h> 
 #include <delays.h> 
 #include <stdio.h> 
  
 #define E LATDbits.LATD7 
 #define RS  LATDbits.LATD6 
 #define lcdport LATB 
 #define _XTAL_FREQ 20000000 
  
 #pragma config WDT=OFF,LVP=OFF,DEBUG=ON 
  
 unsigned int adc_out=0; 
 float adc_value=0; 
 unsigned char voltage[5]; 
  
 void ftoa(float, char *); 
 void lcdcomm(unsigned char); 
 void lcddata(unsigned char); 
 void lcdout(unsigned char); 
 void lcdmsg(const rom char *); 
 void lcdstr(unsigned char *); 
 void lcdblank(void); 
 void lcdclear(void); 
 void lcdinit(void); 
  
 void main (void) 
 { 
     TRISA = 0xFF; 
     TRISB = 0x00; 
     TRISD = 0x00; 
     lcdinit(); 
     lcdcomm(0x80); 
     lcdmsg("RELISYS"); 
     lcdcomm(0xC0); 
     lcdmsg("TECHNOLOGIES"); 
     Delay10KTCYx(1000); 
     Delay10KTCYx(1000); 
     lcdblank(); 
     lcdcomm(0x80); 
     lcdmsg("Channel 1:"); 
     lcdcomm(0x8F); 
     lcdmsg("V"); 
     lcdcomm(0xC0); 
     lcdmsg("Channel 2:"); 
     lcdcomm(0xCF); 
     lcdmsg("V"); 
     OpenADC(ADC_FOSC_32 & 
             ADC_RIGHT_JUST & 
             ADC_4_TAD,ADC_CH1 & 
             ADC_INT_OFF & 
             ADC_VREFPLUS_VDD & 
             ADC_VREFMINUS_VSS, 13); 
     while(1) 
     { 
         SetChanADC (ADC_CH0); 
         Delay10KTCYx(10); 
         ConvertADC(); 
         while(BusyADC()); 
         adc_out=ReadADC(); 
         adc_value=(adc_out*5.0)/1024; 
         ftoa(adc_value,voltage); 
         lcdcomm(0x8A); 
         lcdstr(voltage); 
  
         SetChanADC (ADC_CH1); 
         Delay10KTCYx(10); 
         ConvertADC(); 
         while(BusyADC()); 
         adc_out=ReadADC(); 
         adc_value=(adc_out*5.0)/1024; 
         ftoa(adc_value,voltage); 
         lcdcomm(0xCA); 
         lcdstr(voltage); 
         Delay10KTCYx(1000); 
         lcdclear(); 
     } 
     CloseADC();  
 } 
  
 void lcdmsg(const rom char *Message) 
 { 
     const rom char *Pos = Message; 
     while(*Pos!=0) 
         lcddata(*Pos++); 
 } 
 void lcdstr(unsigned char *str) 
 { 
     int i=0; 
     while(str!='\0') 
     { 
         lcddata(str); 
         i++; 
     } 
 } 
  
 void lcdcomm(unsigned char i) 
 { 
     RS =0; 
     lcdout(i); 
     Delay1KTCYx(2); 
 } 
   
 void lcddata(unsigned char i) 
 { 
     RS =1; 
     lcdout(i); 
     Delay1KTCYx(2); 
 } 
   
 void lcdout(unsigned char dat) 
 { 
     lcdport = dat; 
     E = 1; 
     Delay1TCY(); 
     E = 0; 
 } 
   
 void lcdinit(void) 
 { 
     lcdport=0x00;  
     Delay1KTCYx(40); 
     lcdout(0x30); 
     Delay1KTCYx(15); 
     lcdout(0x20); 
     Delay1KTCYx(15); 
   
     lcdcomm(0x38); 
     lcdcomm(0x0C); 
     lcdcomm(0x01); 
     lcdcomm(0x06); 
     lcdcomm(0x80); 
 } 
  
 void lcdblank(void) 
 { 
     lcdcomm(0x80); 
     lcdmsg("                "); 
     lcdcomm(0xC0); 
     lcdmsg("                "); 
 } 
  
 void lcdclear(void) 
 { 
     lcdcomm(0x8A); 
     lcdmsg("     "); 
     lcdcomm(0xCA); 
     lcdmsg("     "); 
 } 
  
 void ftoa(float value, char *string)  
  {  
      if (value < 0) {  
          *string++ = '-';  
          value = -value;  
      }  
      sprintf(string, (const far rom char *) "%lu.%03u",  
                      (long) value,  
                      (int) ((value - (long) value) * 1000. + 0.5));  
  }

tshuck · Jul 6, 2013

That's good news...

....so what was the problem?

harsha3842 · Jul 6, 2013

error was with OpenADC() function
its resolved and works absolutely fine...

Regards
Harsha

tshuck · Jul 6, 2013

harsha3842 said:
error was with OpenADC() function
its resolved and works absolutely fine...

Regards
Harsha

...that's where the problem was... what was the problem?

ErnieM · Jul 6, 2013

tshuck said:
...that's where the problem was... what was the problem?

Yeah, what he said.

Thread starter	Similar threads	Forum	Replies	Date
W	Book Example for Level Shifter CE Sandwich Also Doesn't Sense	Homework Help	0	Yesterday at 5:41 PM
W	Book Example for Differential Amplifier with Darlington Doesn't make Much Sense	Homework Help	14	Tuesday at 3:54 PM
S	MOSFET doesn't turned off	Analog & Mixed-Signal Design	6	Mar 29, 2024
B	Dehumidifier turns on but doesn't collect water (Solved)	General Electronics Chat	15	Mar 25, 2024
	Integrated IF VCOs doesn't work	Analog & Mixed-Signal Design	6	Mar 1, 2024

ADC to LCD doesn't convert over 2.5v???

Join our Engineering Community! Sign-in with:

ADC to LCD doesn't convert over 2.5v???

harsha3842

donpetru

tshuck

harsha3842

THE_RB

harsha3842

LDC3

harsha3842

tshuck

harsha3842

tshuck

harsha3842

tshuck

harsha3842

tshuck

ErnieM

You May Also Like

Novosense Releases Higher-Performance Op Amps for Automotive

Sound-Powered Sensors Open Another Avenue to Eliminate Batteries

All About Circuits Looks Ahead at Embedded World 2024

Infineon Levels Up Machine Learning Performance With Three New MCUs