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Problems with SHT11 sensor — Parallax Forums

Problems with SHT11 sensor

Sean11Sean11 Posts: 3
edited 2006-10-02 19:38 in BASIC Stamp
i recently purchased·the SHT11 temp/humid sensor for a senior·project and it seems to be giving a temp reading of around 32F and an RHtrue value of 109.5%.· This is impossible.· I put a hair drier on it and the temp does go up along with the RH value.·I have no clue what the problem is and in desperate need of help.·thanks
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Comments

  • Tracy AllenTracy Allen Posts: 6,662
    edited 2006-10-01 04:25
    Did you purchase the SHT11 module from Parallax? Note that the pin numbers on the Parallax module are not the same as the pin numbers in the Sensirion documentation. Be sure to include the pulldown resistor on the sck line.

    What code are you using? Post it here or give us a reference. If there is a raw result value that comes back, it can sometimes help if you insert a DEBUG statement for that in the program. That helps to isolate the problem to before or after the computations.

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    Tracy Allen
    www.emesystems.com
  • Sean11Sean11 Posts: 3
    edited 2006-10-01 18:27
    Yes i did purchase the SHT11 from parallax
    The link below will show you the code and how the sensor is wired.
    http://www.parallax.com/dl/docs/prod/acc/SensirionDocs.pdf

    I am not familiar with PBasic what do you mean by enter a DEBUG statement
    thanks
  • FranklinFranklin Posts: 4,747
    edited 2006-10-01 21:11
    Sean, the program you referenced is full of debug statements. Did you load and run the program>

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    - Stephen
  • Sean11Sean11 Posts: 3
    edited 2006-10-01 23:00
    yes
  • Tracy AllenTracy Allen Posts: 6,662
    edited 2006-10-02 19:38
    Sean, is it the program that is listed in the file that you referenced, and did you type the program yourself, or did you copy and paste or download it from the web site?

    By DEBUG for the raw values, I am looking at this subroutine in the program listed in the pdf:

    SHT_Read_Byte:    
  SHIFTIN  ShtData, Clock, MSBPre, [noparse][[/noparse]ioByte]     ' get byte    
  SHIFTOUT ShtData, Clock, LSBFirst, [noparse][[/noparse]ackBit\1] ' send ack bit    
  INPUT ShtData                                 ' release data line 
  DEBUG ? iobyte      ' <------ADDED THIS DEBUG
  RETURN



    That should display raw iobytes on your screen along with calculated values. What do you see? At that point you will take the raw values and calculate temperature and humidity and compare results with the ones that the stamp has calculated. If they are different, you look at the code, if they are the same (and boh wrong), then you look at the hardware connection and the low level acquisition routine.

    The main thing is for you to understand how the chip and the program work!

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    Tracy Allen
    www.emesystems.com
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