SHT71 temp/humidity sensor - accuracy issues

[hrc]

I'm working on a project where I have a Sensirion SHT71 device tied to a PIC micro.

http://www.sensirion.com/en/sensors/humidity/sensors_devices/sensorSHT71.htm

I'm quite sure the code is working, thats not the issue at hand. If it wasn't then I wouldnt be getting semi valid, or sometimes valid data. Also, the device sends an ACK like I2C when it gets a valid command, and I get that...and I get return data.

What is the problem is getting accurate data. I'm looking for others that have used this part successfully, to find out if there are other things I am not doing right. Can you query it constantly? Or is there settle times? Just need to get some insight.

 

[melone]

Have you put a scope/LA on the interface between the sensor and the Host and verified that you are meeting all of the timing requirements? This could be a simple problem of the timing being on the edge of the specification and sometimes it will work, sometimes it won't work, and sometimes it may partially work.

How are you interfacing with this device? Does your processor (PIC) have a special controller to talk this harware language, or are you doing it via software? If it is done through software, are you sure that it is correct?

Also, verify that the the unit is getting good, CLEAN power (both VDD and GND). Remember, ground bounce is just as bad as supply droop.

Finally, are you following the recommendations stated in 4.8 (don't run SCK and DATA parallel for more than 10cm, to prevent cross-talk)?

 

[hrc]

I've looked at the data pattern on my logic analyzer, and confirmed that its well within the timing parameters. The interface is bit banged since it isn't an I2C, but similar so I can't use the MSSP hardware. Power is clean as well, and the traces are guardbanded as well.

But, did give me an idea to run the clock and data above board just to make sure it isn't crosstalk. Generally running at slow speeds, crosstalk isnt an issue. And it isn't the fact the data is garbage, its like 5degrees off where it should be.