Any one used Lm335 temperature sensor?

[kel]

I'm connecting the Lm335 pins directly to Pic16f877a ADC converter.
can some kindkly post the calculations for lm335 temperature and how the this could be used to calculate the temperature from the temperature read from adc i.e T=read_adc();
thanks

[Ttelmah]

Yes, have used these in the past for a simple 'ambient' temperature sensor.
The 'reading', will depend on the reference voltage you use on the ADC. Hwever assuming 5v supply, and Vref=Vdd, then the reading (with the ADC set to give 10bit accuracy), is:

temp_inDegC=(read_adc()*0.48828)-273.15;

Generally, you can 'cheat' and use integer arithmetic, assuming that a little error is not that important, and if you take:

temp_inDegC_int=(read_adc()-559L)/2;

Gives reasonable results over the 'room tempature' sort of range, without nearly so much work by the processor.

Best Wishes

[kel]

Thanks alot Ttelmah...I can understand the first first equation but i still find it hard to decipher how you arrive to the second equation!

[Ttelmah]

Not 559L/2.
Look where the brackets are.
(reading-559L)/2

You do the subtraction first.
Basically, a 0C reading, gives (nominally) 2.73v. With a 5v reference, this gives a reading of 559. So you subtract this from the incoming reading first. You now have a value of '0', for 0C, rising by just over 2 counts per degree. You will actually get 205 counts for 100C, after the subtraction, so division by 2, gives just over 2% error for the temperature. Not bad, and a lot simpler than the floating point version. :-)

Best Wishes

[gs]

Nice trick! ;)

But I dont understand the use of "L" after the number. Could you explain?

Thanks in advance.


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[Mark]

Long

[kender]

Take a look at thisvery recent thread. The poster had the same plroblem with long.

http://www.ccsinfo.com/forum/viewtopic.php?t=26366