LM35 Output Range

Hi Guys,

I have seen a number of people say that the LM35 produces output voltages between 0V to +1V (0 to 100C). From the datasheet the sensor can range from -40C to 150C, so based upon the mV/C (10mV/C) conversion, +150C would produce +1.5V.

What am I missing. Please find attached the links where I am getting this information from.

http://playground.arduino.cc/Main/LM35HigherResolution

Thanks

Shane

The playground article is talking about resolution rather than range although some of the language is a bit confusing. The assertion that the output is limited to 0-1V appears to be incorrect: the link to the TI datasheet clearly shows 0-1.5v and can even go below zero with a negative supply and pull-down resistor.

As you say the standard setup will measure to 150 easily although the resolution will be limited to about 0.5 degree per step because of the arduino analogRead() mapping 0-5V to count 0-1023. The link describes how to change the 5V reference to 1.1V thereby getting better resolution at the expense of reduced range and possibly reduced accuracy.

Thanks for your reply. I'm new to the Arduino so was a bit confused with conflicting information.

Also, from the link above and as you have mentioned, the design uses the 1.1V internal reference, though the LM35 minimum supply voltage is 4V??

P.S

I am interested in better resolution so I do want to understand the notation of using aRef pin. Any feedback would be much appreciated.

Thanks

The LM35 is still wired the same (V+ to 5V power, GND to ground, Vout to an analog input pin) so gets the same 5V supply as before. Changing the ADC internal reference as per the playground article means that the analog input can only measure 0-1.1V (0 to 110 degrees on the LM35) however the minimum detected temperature step now becomes (110-0)/1023 = 0.1 degree. Whether this matters to you depends on what you are trying to achieve.

Since the LM35 is only guaranteed accurate to +/- 0.5 degree anyway you probably don't gain that much extra information by increasing the precision.

For a quick guide to the difference between precision and accuracy see Accuracy and Precision