SHT15 problem

I have a sht15 temp/ humidity sensor, I’m using the simple sensirion example code. I am taking a reading every 6 seconds, and for some reason I receive a reading the is very off. This is what I get.

Temperature: 76.11 C, Humidity: 77.61 %, Dewpoint: 68.61 C
Temperature: -40.0 C, Humidity: 0.10 %, Dewpoint: -128.63 C
Temperature: 76.27 C, Humidity: 77.53 %, Dewpoint: 68.73 C
Temperature: 75.9 C, Humidity: 78.19 %, Dewpoint: 67.83 C
Temperature: 74.94 C, Humidity: 0.10 %, Dewpoint: -68.73 C
Temperature: 76.35 C, Humidity: 77.64 %, Dewpoint: 68.84 C
Temperature: 75.12 C, Humidity: 78.20 %, Dewpoint: 67.87 C
Temperature: 75.1 C, Humidity: 0.10 %, Dewpoint: -68.70 C
Temperature: 76.42 C, Humidity: 77.73 %, Dewpoint: 68.95 C
Temperature: 75.23 C, Humidity: 78.13 %, Dewpoint: 67.95 C
Temperature: 75.9 C, Humidity: 0.10 %, Dewpoint: -68.67 C
Temperature: 76.49 C, Humidity: 77.63 %, Dewpoint: 68.98 C

DONT WORRY ABOUT THE TEMP READINGS THERE CONVERTED TO F

Yes, I looked over those sections and made changes accordingly.

What "changes" did you make? This looks like a communication problem (signal integrity) - can you provide a detailed description of how you hooked up the sensor?

That -40C reading on the second line is very suspicious. That's what happens if the SHT15 hasn't yet initialised properly and a reading is taken, so it may be a timing problem in the code.

Perhaps try it with an existing library like this one just to verify that the hardware is doing what it should:

http://github.com/practicalarduino/SHT1x

Jon Freetronics: www.freetronics.com Practical Arduino: www.practicalarduino.com

That -40C reading on the second line is very suspicious. That's what happens if the SHT15 hasn't yet initialised properly and a reading is taken, so it may be a timing problem in the code.

Possibly. There are also 4 bogus humidity measurements which is what led me to suspect a connection issue. Maybe it's time to add an option for CRC checking. I've been playing with the "Sensirion" library from the Playground and might give this a try. Have you considered it for your SHT1x library? Sensirion's inclusion of the 4 LSBs of the User Register in the CRC calculation complicates things somewhat...

Carl