[SOLVED] Problem with LM35 negative temperature reading

Praveen Kumar P S · Aug 23, 2014

Hello friends...

This program is for reading the Temperature and display it on a lcd display at the same time the pic serially transmit the temperature.....My program works.....:roll::roll:..But it is not displaying any negative temperature....:bang::bang::bang:

plzz help guys...............

Here is my code:::

Code:

#include <18f4550.h>
#device ADC=10
#fuses HS,NOWDT,NOPUT,NOPROTECT,NODEBUG,BROWNOUT,NOLVP,NOCPD,NOWRT 
#use delay(crystal=48000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7)
#include<flex_lcd416.c>
void main() 
{ 
unsigned int8 t;
lcd_init();
lcd_gotoxy(4,1);
lcd_putc("Temperature\n");
setup_port_a(ALL_ANALOG);
setup_adc( ADC_CLOCK_INTERNAL);
setup_adc_ports(AN0);
for(;;)
{
set_adc_channel(0);
delay_ms(10);
t = read_adc()/2;
lcd_gotoxy(6,3);
printf("Temp::\t%3.0u \xDFC\n\r",(unsigned int8)t);
printf(lcd_putc,"%3.0u \xDFC ",(unsigned int8)t); 
delay_ms(10);

}
}

KlausST · Aug 23, 2014

Hi,

Is your adc able to decode negative voltage?

If yes, did you negative bias with resistor your lm35 output?

Klaus

horace1 · Aug 23, 2014

your variables are unsigned, e.g.

Code:

unsigned int8 t;

and the printf() conversion specifications etc are for unsigned types
if you expect negative values should you be using signed types?

andre_luis · Aug 23, 2014

Probably the printf() formatting parameter %u would also conflict to the signed variable type.

Praveen Kumar P S · Aug 24, 2014

KlausST said:
Hi,

Is your adc able to decode negative voltage?

If yes, did you negative bias with resistor your lm35 output?

Klaus

I connect output of lm35 directly to AN0 pin of the pic.....i didnt have a -ve bias with resistor.....
why is the resistor for.....??
thank you....

plzz help

Praveen Kumar P S · Aug 24, 2014

i changed my program but still no effect...........
here is my new code..

Code:

#include <18f4550.h>
#device ADC=10
#fuses HS,NOWDT,NOPUT,NOPROTECT,NODEBUG,BROWNOUT,NOLVP,NOCPD,NOWRT 
#use delay(crystal=48000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7)
#include<flex_lcd416.c>
void main() 
{ 
signed int8 t;
lcd_init();
lcd_gotoxy(4,1);
lcd_putc("Temperature\n");
setup_port_a(ALL_ANALOG);
setup_adc( ADC_CLOCK_INTERNAL);
setup_adc_ports(AN0);
for(;;)
{
set_adc_channel(0);
delay_ms(10);
t = read_adc()/2;
lcd_gotoxy(7,3);
printf("Temp::\t%3.0d \xDFC\n\r",(signed int8)t);
printf(lcd_putc,"%3.0d \xDFC ",(signed int8)t); 
delay_ms(10);

}
}

guys...any hing wrong with my code...plz help
thank u....

paulfjujo · Aug 24, 2014

hello,

What is the specsheet of your LM35
is it a LM35DZ or a LM335
LM335 can measure negative temperature, LM35DZ can NOT ...

if you can use 4.096V as +VREF and use -VREF with a resistor divider by 2 sor -VREF=2,048V
you can have a scale of 2048mV for 1024 points
and measure from -68.2°C up to 136.6°C with a resolution of 0.2°C
see table..

problem:
signed int8 ?
an int is 16 bits..
why not simply use

Code:

int t;    // must be an int signed

because read_adc must be an integer ( with only 10 bits used inside the result)

%3.0 decimal, is reserved for floating point
you must write %3d

Code:

printf("Temp::\t%3d \xDFC\n\r",t);

why divide Adc result by 2 ?
you measure is a raw measure in points, you need to convert it in °C or °F
see correspondance table for a LM335 ..
Positive is upper 2730mV = 0°Kelvin

Praveen Kumar P S · Aug 25, 2014

[Merged]CanT read data from sensors....!!!

Hello guys....
i dont why my program is not working.....It read values from the sensors...but not showing any correct temperature and my humidity sensor output always zero.....
here is my code....:::

Code:

#include <18f4550.h>
#device ADC=10
#fuses HS,NOWDT,NOPUT,NOPROTECT,NODEBUG,NOLVP,NOCPD,NOWRT,NOMCLR,INTRC_IO,NOPBADEN,BROWNOUT,PUT
#use delay(crystal=48000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7,ERRORS)
#include<flex_lcd416.c>

void main()
{
unsigned int8 t0,t1,T;
unsigned int8 h;
lcd_init();
setup_adc(ADC_CLOCK_INTERNAL);
setup_adc_ports(ALL_ANALOG);
set_adc_channel(0);
delay_ms(10);
t0=read_adc()/2;
delay_ms(10);
set_adc_channel(1);
delay_ms(10);
t1 = read_adc()/2;
delay_ms(10);
T=t0-t1;
lcd_gotoxy(1,2);
printf(lcd_putc,"Temp::\t%3.0d \xDFC ",(signed int8)T);
printf("Temp::\t%3.0d \xDFC\r",(signed int8)T);

set_adc_channel(2);
delay_ms(10);
h=read_adc()/2;
delay_ms(10);
lcd_gotoxy(1,1);
printf(lcd_putc,"Humidity::%3.0u",(unsigned int8)h);
output_high(PIN_B3);


}

plzz help me........:bang::bang::bang::bang::bang::bang:

milan.rajik · Aug 26, 2014

Re: [Merged]CanT read data from sensors....!!!

Here I am attaching LM35 firmware and Proteus simulation. If you need more precise measurement then I will use Vref+ and make it. :thumbsup:

[SOLVED] Problem with LM35 negative temperature reading

Praveen Kumar P S

Member level 4

KlausST

Advanced Member level 7

Praveen Kumar P S

horace1

Advanced Member level 5

Praveen Kumar P S

andre_luis

Super Moderator

Praveen Kumar P S

Praveen Kumar P S

Member level 4

Praveen Kumar P S

Member level 4

paulfjujo

Advanced Member level 4

Praveen Kumar P S

Praveen Kumar P S

Member level 4

milan.rajik

Banned

Attachments

Praveen Kumar P S

Similar threads

[SOLVED] Problem with LM35 negative temperature reading

Member level 4

Advanced Member level 7

Advanced Member level 5

Super Moderator

Member level 4

Member level 4

Advanced Member level 4

Member level 4

Banned

Attachments

Similar threads

Privacy & Transparency

Privacy & Transparency