CCS/MSP430FR4133: Calculate temperature using external LMT86 temperature sensor.

Marcel Pirlog

Part Number: MSP430FR4133
Other Parts Discussed in Thread: LMT86

Tool/software: Code Composer Studio

Hello,

I have a msp430fr4133 and one LMT86 temperature sensor. I connect sensor at P8.0 -> A8 ( Analog input ). I configurate ADC using driverlib with 10bits resolution "ADC_configureMemory(ADC_BASE, ADC_INPUT_A8,ADC_VREFPOS_AVCC,ADC_VREFNEG_AVSS);".

I see in user guide at section 2.2.9 this formula: T = 0.00355 × (VT – V30ºC) + 30ºC. http://www.ti.com/lit/ug/slau445i/slau445i.pdf

I found in datasheet at section 6.10 https://www.ti.com/lit/ds/symlink/msp430fr4133.pdf V30C.

I tried with this formula to calculate temperature received from ADC and the answer not is good.

#define CALADC_15V_30C *((unsigned int *)0x1A1A)
#define CALADC_15V_85C *((unsigned int *)0x1A1C)

...

adcRes = ADC_getResult(ADC_BASE); // for example reived 577

//Formula I

tempInCD = 0.00355 * ( 577 - CALADC_15V_30C ) + 30;

//Formula II

tempInCD = (adcRes - CALADC_15V_30C ) * ( 85 - 30 ) / ( CALADC_15V_85C - CALADC_15V_30C ) + 30;

With both formulas get a wrong answer.

Before tempInCD do I have to do other operations with "adcRes"?

Please give me an explication step by step with correct formula.

over 4 years ago

0 Wei.Jetim Zhao over 4 years ago

TI__Genius 13215 points

Hi Marcel,

The formula and calibration data in the User's Guide and Datasheet is for the on chip internal temperature sensor not any external temp sensor.

You should take the parameters of LMT86 datasheet for you calculation.

0 Marcel Pirlog over 4 years ago in reply to Wei.Jetim Zhao

Prodigy 110 points

I search on E2E and read morea questions and answer but I did not find the answer to my question. Is more question with internal temperature sensor.

I see LMT86 datasheet http://www.ti.com/lit/ds/symlink/lmt86.pdf#page=9 but without success.

I did not understand how to use the formulas in section 8.3 and how to integrate them into my program.

0 Wei.Jetim Zhao over 4 years ago in reply to Marcel Pirlog

TI__Genius 13215 points

Hi Marcel,

The section8.3 gives you very detailed LMT86 Transfer Table as well as the parabolic equation which could calculate T from Vtmp(mV). So what is your specific question or problem?

0 Marcel Pirlog over 4 years ago in reply to Wei.Jetim Zhao

Prodigy 110 points

ADC give me a voltage from sensor output pin ( 578 mV ). The problem is:

How to convert this value in celsius degrees or what is the "algorithm" for this conversion with correct formula ?

How do we have the internal sensor that calculation formula. Probable exist for every temperature sensor family one specific formula and I don't find this formula for LMT86.

This is my problem.

I try some formula for arduino but don't work in my case.

0 Wei.Jetim Zhao over 4 years ago in reply to Marcel Pirlog

TI__Genius 13215 points

Hi Marcel,

You should read the section8.3 which tells you very detailed about your first question.

The formula you are finding is equation 2 in section8.3.

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CCS/MSP430FR4133: Calculate temperature using external LMT86 temperature sensor.