Reading negative Temperature from LM35


#1

Hello,
Nowadays, i am working on the project that requires to retrieve negative temperature values.
But the BOLT ADC pin has 1 Bit resolution in range 0 - 1V. So how could i read negative temperature from BOLT A0 pin using the LM35 sensor ?


#2

@kashifofme I am not sure about the exact way forward but I believe that 0V may not correspond to 0 degree celsius. You could try keeping the sensor in a subzero temperature region and see what value it records. Let me know.

Here is a product built on Bolt https://www.boltiot.com/bthm.html that measures up to -50 celsius.

cc: @vinayak.joshi


#3

Hi kashifofme,
Please read a datasheet
http://www.ti.com/lit/ds/symlink/lm35.pdf
A negative voltage is required for measurement at negative temperature using LM35.

Temperature sensors with analog output that do not need negative voltage exist.(ex.LM60, LM61)


#4

hi @ppv the link is showing error.

my lm35 sensor not showing the actual temperature in graph like -2 C or -30 ^c, How is this possible?


#5

Hi,

If you connect the sensor as it is to the Bolt WiFi module, it will only be able to provide +ve readings to the system.

As mentioned by @suetsugu, it is not possible to use an LM35 sensor to measure -ve readings on it’s own.

It would be best to interface a sensor such as LM60 and LM61 to the Bolt if you want to measure -ve voltages.


#6

yes but in data sheet of LM35 it is showing that it can be use to take reading from -50 to 150 . so why it is not useful to measure the -ve readings.


#7

@pvthakkar10,

This is because the LM35 gives a -ve output for -ve temperature readings, while the Bolt can only sense voltage in the range of 0 to 1v.