i need help how to calibrate lm35 to read accurately or near to normal body temperature. i'm still a newbie in arduino. 
here's my code.
const int inPin = A1; // analog pin
void setup()
{
Serial.begin(9600);
}
void loop()
{
int value = analogRead(inPin);
float celsius = (value / 1023.0 ) * 500; //( 5.0 * value * 100.0) / 1024.0;
Serial.print(celsius);
Serial.println(" degrees Celsius ");
delay(1000); // wait for 15 seconds
}
What makes you think it's not accurate? Maker's datasheet says it's good for .5 degree.
delay(1000); // wait for 15 seconds
Interesting comment.
yah i know. but when i tried measuring my body temperature, i just got 34.70 degrees Celsius. suppose to be 36 or 35 degrees celsius. is there a way to calibrate this?
retrolefty:
delay(1000); // wait for 15 secondsInteresting comment.
sorry for that. i was trying delay for 1 second and 15seconds. i didn't notice it.
Supposed to be 35 or 36?... which is it at the moment? 34.7 IS 35 within the limits of what the makers say.
(Wikipedia tells me 37, btw.....)
And where were you taking the reading?- is that in itself a reliable, recognised place to read the body's temp? My guess is that it's not transferring to the LM35 effectively. If you have a recognised way of taking the temp- a clinical thermometer under the tongue, or rectally, or those electronic ear ones, then you could compare I guess and adjust your reading accordingly if the discrepancy is consistent over a number of readings on different subjects.
i just got 34.70 degrees Celsius. suppose to be 36 or 35 degrees celsius. is there a way to calibrate this?
Why do you think 34.7 is wrong? Your body temperature rises and falls during the day.
float celsius = (value / 1023.0 ) * 500;
Is your voltage EXACTLY 5.0 volts?
JimboZA:
Supposed to be 35 or 36?... which is it at the moment? 34.7 IS 35 within the limits of what the makers say.(Wikipedia tells me 37, btw.....)
And where were you taking the reading?- is that in itself a reliable, recognised place to read the body's temp? My guess is that it's not transferring to the LM35 effectively. If you have a recognised way of taking the temp- a clinical thermometer under the tongue, or rectally, or those electronic ear ones, then you could compare I guess and adjust your reading accordingly if the discrepancy is consistent over a number of readings on different subjects.
ah sorry. 37 i mean. thank you for that. I put it in my armpit. usually some doctors put it that way. i tried it using a soldering iron and it varies. the only thing that bother me is that i can't get the normal body temperature. 
The only way you'll know for sure is to use a clinical thermometer and compare the two. Do that lots of times with a few friends and if it's consistently out by a constant amount well you could just add that in each time you take a reading on the LM35.
PaulS:
i just got 34.70 degrees Celsius. suppose to be 36 or 35 degrees celsius. is there a way to calibrate this?
Why do you think 34.7 is wrong? Your body temperature rises and falls during the day.
sorry 37 i mean. yah actually. i can't get the normal body temperature.
float celsius = (value / 1023.0 ) * 500;Is your voltage EXACTLY 5.0 volts?
i'm using the 5volts in my mcu. is that okay?
JimboZA:
The only way you'll know for sure is to use a clinical thermometer and compare the two. Do that lots of times with a few friends and if it's consistently out by a constant amount well you could just add that in each time you take a reading on the LM35.
yes, i did it already. using clinical thermometer, i got 36 degrees Celsius while LM35 just 34.7. ...
okay, tomorrow i'll do it with my friends. Thank you 
ahm btw, what do you mean just add that in each time i take a reading on LM35?
i'm using the 5volts in my mcu. is that okay?
It's fine IF the voltage really is 5.0V. But, the question is it it really?
How are you powering the Arduino? Have you measured the exact voltage?
Since your temperature reading is inaccurate, or so you think, and since the temperature is linearly related to the supply voltage, you need to eliminate voltage as a factor. And, the only way to do that is measure it.
By the way, I just found this which states:
Axillary temperatures are an external measurement taken in the armpit or between two folds of skin on the body. This is the longest and most inaccurate way of measuring body temperature, the normal temperature falls at 97.6 °F or 36.4 °C.
... so you should expect about half a degree cooler there it seems, and poses the question: did you leave the LM in your pit long enough?
I put it in my armpit. usually some doctors put it that way. i tried it using a soldering iron and it varies.
You put a soldering iron in your armpit??
I think your problem has been solved, regarding the armpit showing a lower than actual body temperature reading.
Under the tongue is better, however, I have to ask if you have the sensor sealed and waterproof. That could throw off your reading where-ever you take it.
Instead of using delay(), which does nothing, why not collect more readings and average them?
And... don't forget to use code tags.
PaulS:
It's fine IF the voltage really is 5.0V. But, the question is it it really?How are you powering the Arduino? Have you measured the exact voltage?
Since your temperature reading is inaccurate, or so you think, and since the temperature is linearly related to the supply voltage, you need to eliminate voltage as a factor. And, the only way to do that is measure it.
i just figured out 4.62 volts only. then i make some changes in my codes and still doesn't give me the normal body temperature. is there other way?
cdelig:
i just figured out 4.62 volts only. then i make some changes in my codes and still doesn't give me the normal body temperature. is there other way?
But you don't know it's wrong unless you compare it against a known good measure like a clinical thermometer. Until you do that, you're pissing in the dark, and might as well just ditch the LM35 and hardcode the display "temp = 37 degrees" because you seem to think that's what it is.
JimboZA:
By the way, I just found this which states:Axillary temperatures are an external measurement taken in the armpit or between two folds of skin on the body. This is the longest and most inaccurate way of measuring body temperature, the normal temperature falls at 97.6 °F or 36.4 °C.
... so you should expect about half a degree cooler there it seems, and poses the question: did you leave the LM in your pit long enough?
ahhh okay but why is it clinical thermometer can get the exact normal body temperature?
yes, i was using velcro strap where my LM35 attached in it.
cdelig:
PaulS:
i just got 34.70 degrees Celsius. suppose to be 36 or 35 degrees celsius. is there a way to calibrate this?
Why do you think 34.7 is wrong? Your body temperature rises and falls during the day.
sorry 37 i mean. yah actually. i can't get the normal body temperature.
float celsius = (value / 1023.0 ) * 500;Is your voltage EXACTLY 5.0 volts?
i'm using the 5volts in my mcu. is that okay?
What he was implying is that an arduino board is rarely operating at exactly +5.0000 vdc as your formula implies. If powered from the USB then the voltage will be a nominal 5 volts with a +/- tolerance and if powered from the on-board 5 volt regulator the voltage will be 5 volt +/- some different tolerance. The subject of accuracy and calibration can be quite complex (and frustrating).
Bottom line, Accuracy for a measurement gets more complex (and expensive) the more you expect from it. 