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TMP36 and Launchpad 430FR6989

William Pinyan
Prodigy 60 points
Other Parts Discussed in Thread: LM35, LMT70, LMT87

After viewing Adrian's recent video on sub01GHZ, I ordered several boards for a project.  The project measures temperatures in various rooms as well as a walk-in freezer.

I am using a TMP36 because it's characteristics are in the range I need, but when connecting to PIN 23 on the launchpad, the analogRead returns 158 mv instead of the 125(+-) mv expected for 75 deg. F.  In fact, I measure 125 mv on a meter while the analogRead is saying 158 mv.  The circuit puts out 1mv per deg F with a 58 degree offset (see diagram from TMP36 datasheet.

The erroneous reading makes the room appear to have a temp of 100 deg. F instead of 75.  I could just subtract an additional 25, but that seems hoky and would not guarantee the formula to work linearly as intended for the minus 30 degree to 80 degree expected range for my project.

Thanks,

T

  • 0
    TI__Genius 15760 points
    Hi William,

    If you can measure the expected voltage from the Temp sensor, using your meter, then your problem should be review it by the MSP team. I will move this question to their forums. They might be able to provide some recommendations.

    Please provide an schematic of your circuit, this might help us to identify the problem.
  • 0
    TI__Genius 15760 points

    Hi William,

    We are curious to know what is your application. We have a great selection of Texas Instruments analog temperature sensors that can be a better suit for your application and we will be able to provide support when debugging. 

    I would suggest you take a look at LMT8x family, such as LMT87 device. It is cost-effective and more accurate than your current solution. If even more accuracy is needed you can take a look at LMT70. Besides those, LM35 would be exact replacement for your current solution.