LM35 Testing

koolguy

Active Member

• Jul 14, 2015

• #1

Hello,
I have LM35 how to test it i have doubt it is damage, how to test it with multi meter??
https://embedded-lab.com/blog/?p=4867
according to this the i have used Vcc 6V so, output is 0.005V it changes in between, why?
**broken link removed**

 

Last edited: Jul 14, 2015

ericgibbs

Well-Known Member

Most Helpful Member

• Jul 14, 2015

• #2

hi,
Have you read the datasheet.?
E

 

Attachments

• LM35.pdf

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koolguy

Active Member

• Jul 14, 2015

• #3

yes, but how to test with multi meter i am confused.

 

ericgibbs

Well-Known Member

Most Helpful Member

• Jul 14, 2015

• #4

Try this, post what you measure.

 

Attachments

• AAesp01.gif

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W

Wp100

Well-Known Member

• Jul 14, 2015

• #5

You just set it up as shown in that link. Pos and Neg to any voltage 4.5 to 9v DC and the middle leg to your Volt meter red lead on the 2v DC range and the black lead to the voltage negative.

Have just done that on my LM35 and the meter reads 0.236v which = 23.6deg C. The display is stable, but if you have the bare sensor in a cool draught it may just move up and down.

If you still get 0.005v then supsect its connected wrong or damaged.

 

Ian Rogers

User Extraordinaire

Forum Supporter

Most Helpful Member

• Jul 14, 2015

• #6

Remember that the 'DP' and the 'DT' packages have different pinouts!!!

 

W

Wp100

Well-Known Member

• Jul 14, 2015

• #7

koolguy said:

Hello,
I have LM35 how to test it i have doubt it is damage, how to test it with multi meter??
https://embedded-lab.com/blog/?p=4867
according to this the i have used Vcc 6V so, output is 0.005V it changes in between, why?
**broken link removed**

Click to expand...

Agree with the LM35s pinout shown in the Embedded link.

To me the pantech link you now show has pin1 and 3 the wrong way around for a t092 device.

 

koolguy

Active Member

• Jul 15, 2015

• #8

it is lm35 dz

 

koolguy

Active Member

• Jul 15, 2015

• #9

It is showing .009V

 

W

Wp100

Well-Known Member

• Jul 15, 2015

• #10

koolguy said:

It is showing .009V

Click to expand...

If you have connected it up as that Embedded link or Erics picture then you should be getting a sensible reading, as you are not , can only concluded the sensors duff, you need to get a new one.
( just reversing the + and - connections for a split second are enough to blow them)

There is a chance it is working fine, if you are testing it in a freezer where the temp is 0c ..

 

koolguy

Active Member

• Jul 17, 2015

• #11

Hello,
I have changed the LM35 please tell how to convert it to *C
the ADC is working fine at 5V reference. left justified
lm35 is giving 10mV/*C
so, there is 10 bit ADC 2^10=1023bits
5/1023= 4.8mV

so, how to convert in *C

#include <htc.h>

__CONFIG( BOREN_OFF & PWRTE_ON & WDTE_OFF & FOSC_HS);
#define _XTAL_FREQ 20000000


void main()
{
TRISB=0X00;
PORTB=0X00;
TRISA = 0xff ;
ADCON1=0b00000000;
ADCON0=0b10000001;//000 = channel 0, (RA0/AN0)
ADIF=0;
ADIE=1;
PEIE=1;
while(1){
__delay_us(10);
GO_DONE=1;
__delay_us(10);

PORTB=ADRESH;
PORTB=0X00;
__delay_ms(200);
PORTB=0Xff;
__delay_ms(200);

}
}

 

ericgibbs

Well-Known Member

Most Helpful Member

• Jul 18, 2015

• #12

hi,
One option is to amplify the LM35 output, to give 5v as an input to the PIC.
The working range is +2C thru 150C.
I usually scale the amp to give 4.88v out at 100C, this gives a ADC count of 1000 for 100C, so a +/-0.1C resolution.
The maths are easier for this scaling.

 

koolguy

Active Member

• Jul 18, 2015

• #13

How to convert directly the 10bits result to digits?

 

Ian Rogers

User Extraordinaire

Forum Supporter

Most Helpful Member

• Jul 18, 2015

• #14

You are better off referencing the ADC to its minimum possible ( I'm sure that its 2.2v) That way you can get the best resolution.. But

degrees C = (ADCin * 5v / 1024) * 100 ....

 

koolguy

Active Member

• Jul 18, 2015

• #15

I AM USING 5v REFERENCE.

 

Ian Rogers

User Extraordinaire

Forum Supporter

Most Helpful Member

• Jul 18, 2015

• #16

koolguy said:

I AM USING 5v REFERENCE.

Click to expand...

So!!

degrees C = (ADCin * 5v / 1024) * 100 .... As you won't be using floating point!!

degrees C = (ADCin * 500 / 1024) will give you what you want!

 

koolguy

Active Member

• Jul 18, 2015

• #17

degrees C = (ADCin * 500 / 1024) will give you what you want!

Click to expand...

How to get this equation need to understand.

C:

#include <htc.h>
__CONFIG(LVP_OFF & BOREN_OFF & PWRTE_ON & WDTE_OFF & FOSC_HS);
#define _XTAL_FREQ 20000000
unsigned char digits[] = {  0b00010000,0b01111101,0b00100010,0b00101000,0b01001101,0b10001000,

0b10000000, 0b00111101,0X00,0b00001000};

void main(){
TRISD=0X00;   
TRISB=0X00;
PORTB=0X00;
TRISA = 0xff ;
ADCON1=0b00000000;
ADCON0=0b10000001;//000 = channel 0, (RA0/AN0)
ADIF=0;
    ADIE=1;
    PEIE=1;
while(1){
    __delay_us(10);
GO_DONE=1;
    __delay_us(10);

unsigned char x=0;

x=ADRESH;
PORTD = 8;
x=x%10;
PORTB=digits[x];
__delay_ms(5);
PORTB=0X00;
x=ADRESH;
PORTD = 4;
x=(x/10)%10;
PORTB=digits[x];
__delay_ms(5);
PORTB=0X00;
x=ADRESH;
PORTD = 2;
x=x/100;
PORTB=digits[x];
__delay_ms(5);
PORTB=0X00;
x=ADRESL;
x=x%10;
PORTD = 1;
PORTB=digits[ADRESL];    // just for test on display working or not
__delay_ms(5);
PORTB=0X00;
       
    }
}

 

koolguy

Active Member

• Jul 18, 2015

• #18

how to get ADRESH and ADRESL IN
unsigned int x=0;
LEFT JUSTIFICATION?

 

Ian Rogers

User Extraordinaire

Forum Supporter

Most Helpful Member

• Jul 18, 2015

• #19

Left justification??? It is easier in right justification..

11111111 11xxxxxx.. all this needs shifting 6 bits.. This is mainly for 8 bit compatibility..
xxxxxx11 11111111.. Here you can just read into a 16 bit number...

Justification is usually in ADCON1, bit 7..

C:

unsigned int result;

result = (( unsigned int) ADRESH << 2) + (ADRESL >>6); // Left!

result = (unsigned int) ADRESH << 8  + ADRESL;  //Right!

 

koolguy

Active Member

• Jul 19, 2015

• #20

Hello,
it is not working showing 15 pls have a look to code at 26mV from LM35