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dkinzer
Site Admin
Joined: 03 Sep 2005
Posts: 2499
Location: Portland, OR
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Posted: 25 July 2006, 22:26 PM Post subject: Sensirion SHT71 Code |
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The attached file contains code to interface with the SHT71. It may also work with the SHT11 and other similar devices.
[Edit] The .zip file has been updated with source code that includes the dew point calculation code and a project file that can be used to build a stand alone test application. Also, subsequent to the original posting, it has been confirmed that this code works with the SHT11.
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sensirion71.zip |
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2.47 KB |
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Last edited by dkinzer on 27 July 2006, 15:39 PM; edited 1 time in total |
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zbasicandy
Joined: 26 Jan 2006
Posts: 193
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Posted: 26 July 2006, 12:56 PM Post subject: SHT1x |
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Here is the dew point calculation PDF from the manufacturer.
The data I/O pin should have a 4.7K pullup along with a series "current limiting resistor 330 ohm / 1 K.
In case you cannot get a reading a recommended 4.7K pulldown should be on the clock pin.
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Dewpoint_calculation_E_C1.pdf |
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148 KB |
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4930 Time(s) |
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dkinzer
Site Admin
Joined: 03 Sep 2005
Posts: 2499
Location: Portland, OR
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Posted: 26 July 2006, 15:18 PM Post subject: |
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Thanks. I probably should have included that calculation. Here is a function that implements their calculation that can be added to the module.
| Code: | '----------------------------------------------------------------------
'
'' SHT_DewPoint
'
' Calculate the dew point given the temperature (in Celsius) and
' relative humidity.
'
Public Function SHT_DewPoint(ByVal T As Single, ByVal RH as Single) as Single
Dim H as Single
H = ((log10(RH) - 2.0) / 0.4343) + (17.62 * T / (T + 243.12))
SHT_DewPoint = 243.12 * H / (17.62 - H)
End Function |
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zbasicandy
Joined: 26 Jan 2006
Posts: 193
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Posted: 26 July 2006, 15:39 PM Post subject: SHT71 |
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The SHT11 (as oppose to the SHT71) can be protected by a filter "SF1" from supplier www.Newark.com.
| Quote: | | The SF1 filter cap provides IP67 protection against water, dust and other contaminants for the humidity and temperature sensors SHT10, SHT11 and SHT15. It is a low cost part and very easy to use. The filter cap consists of a single piece of polypropylene including a filter membrane. It fits the outer dimensions of the SHT1x sensors and allows for compact system design. It also serves as an adaptor for mounting the sensor directly into the wall of a housing. Using a sealing ring, this results in a waterproof mounting solution. |
If you buy the 8 pin dip mount SHT11 with internal pullup and current limit from www.Parallax.com for $30 you cannot use this filter cap.
Save some $ money and buy a SHT11 chip from www.newark.com for ~$10 cheaper and add your own resistors. (Precision wiring/soldering is needed)
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zbasicandy
Joined: 26 Jan 2006
Posts: 193
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Posted: 27 July 2006, 13:49 PM Post subject: SHT11 |
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The above algorithm works fine on our ZX-40 microcontrollers using the SHT11. No changes were made to the "code module" ... except for the pin numbers. 
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