Anyone with Sensirion HT11 experience ?

[picman2]

sensirion pic reading

Hi all

I have successfully interfaced an HT11 temperature & humidity sensor to a PIC, but comparing the readings with other thermometers I have always too much temperature (i.e. 25 C vs 21 C real) and too low humidity (25% vs 35% real).

I have soldered HT11 on a 8 pin DIL socket, and I think it's not affected by other on board components, everything is on a perf board with plenty of space around.

I have checked with two HT11 sensors, readings are almost equal.

I have implemented CRC checks on data returned by sensor, and I have no communications error, of course.

Help ! I'm going crazy !

Picman

 

[Kripton2035]

pic microcontroller and sensirion

didnt you by mistake turn on the heater ??
it's explained in the status register datasheet on the sensirion web site. it ups the temp by around 5 degres.
or may be you make a mistake in the conbination of low and high order byte when you read the 14 bits temp ??

 

[picman2]

I can surely exclude both cases:

1) I have implemented the command to turn on/off the heather, and if I turn it on I read the expected increment of temperature.

2) If I would have inverted MSB and LSB, reading would be totally scrambled. Also the MSB is easily recognized because it has the most significant bit stuck at zero.

I'm really puzzled.
I tried the reading as soon as I power up the HT11, so I can exclude board self heating, too.

In this istant I read on both my reference termometers 22 C / 37% while HT11 gives 24.7 C / 28.4%

Cheers...

PicMan

 

[Kripton2035]

can you try to read another temperature/humidity for example if you put the sht11 in your freezer ?? to see if the temp step is the same or if it is proportionnal..

 

[assuh102]

Hi, I have the same experience in using Sensirion SHT11. The SHT11 i'm using was mounted in 8-PDIP by Parallax. https://www.parallax.com

I was using the software from Sensirion website on C8051F005 3,3V Microcontroller from Silicon Laboratories.

I've tried to change the voltage supply for SHT11 and surprisingly the results are strange, the temperature was increase when the supply voltage was decreased.

For 5 V supply the temperature was 6-7º C lower than the actual
For 4 V supply the temperature was 4-5º C lower than the actual
For 3,3 V supply the temperature was 2-3º C higher than the actual

while the datasheet say the SHT11 can be supplied within 2.4 to 5 Volt range.

Where did I go wrong ?

Can anyone help?

Thanx

assuh102

 

[TechToys]

I have soldered HT11 on a 8 pin DIL socket, and I think it's not affected by other on board components, everything is on a perf board with plenty of space around.

After soldering, have you put the sensor in 20-30C & (>74%RH) for 48 hours before using it?

John Leung