assistance regarding SHT11, sht giving crc error

hope every thing would be fine with you all..
i needed some assistance regarding SHT11, I was intending to use sht11 in my project, but i get some unusual problem, after interfacing it to an AVR ,and using a code that had been tested and verified by others i always get temp reading as -39.7 'c ... i am using 3.3 V VCC , more over if I implement CRC check i get CRC error, How should i Proceed?

Hi,

Have you fitted the 100nf cap onto the sensor ?
Have you got the Data line and possibly the CLK line pulled up ?

For testing purposes are you using short leads, under 1 mtr, to the SHT11 ?

yes i had tried that too... moreover i also did came to know that the sck pin of sht is not meant to be attached to the sck of AVR, even after making the changes the result is same again....
I wonder what can be the cause of CRC error?

Added after 5 minutes:

and yes, i came to know from the data sheet that the value of D1 in formula is 39.7 for 3.5V hence this shows that the sensor reading is zero that makes d2.sensor reading=0 and hence i get 39.7 negative reading...

Also i can connect to it , and can access the sht as the software does recognise it and even asks to wait until sensor reading is ready.....quite confusing for me.... I had searched in many forums but couldnt find any thing like that .... either i am making some serious mistake in interfacing or its my badluck.... i have tried two such circuits, with different sensors both sht11 and even different program... still same errorr

Hi,

moreover i also did came to know that the sck pin of sht is not meant to be attached to the sck of AVR, even after making the changes the result is same again....

Click to expand...

Well its often refered to as an SPI device but not in practice. It is a custom serial protocol that does not use the micros own SPI hardware.

and yes, i came to know from the data sheet that the value of D1 in formula is 39.7 for 3.5V hence this shows that the sensor reading is zero that makes d2.sensor reading=0 and hence i get 39.7 negative reading...

Click to expand...

Think its too co-incidental that you are getting 39.7 as a reading - have you been able to look at the 14bit raw temp data to see what is actualy being sent.

Also, it should be built into your code that your micro only makes one reading per second maximum.

Cannot help with your code as mine is in Pic assembler and I was lucky enough to find a working example on the web; its a difficult routine for the hobbyist to code - however have you seen the two code examples on the Sensirion SHT11 site on in C and one for the 8051 - they might give you some guidance but seem to remember some web comment about folk not being able to get those examples to work ..?

For such an expensive sensor they do not make it easy to use, plus many sites never mention that there is a protective cover you can buy for it.
https://uk.farnell.com/sensirion/sf...ssellid=1399624&crosssell=true&in_merch=true&


good luck !

well i am getting -39.7'c... i would try to find some tested code and try it then,
thanks alot for ur help Wp100!!!

hi sherazi

just go here although it is in pic basic but at least give you an idea to do CRC for sht sensor

https://www.picbasic.co.uk/forum/showthread.php?t=7450&highlight=humidity+sensor

Regards
Fragrance