LPS33HW - false reading both pressure and temp

[Dimitar Dyakov]

Posted on April 03, 2018 at 00:53

Hi guys,

I have STEVAL-MKI183V1 connected to stm32l476rg NUCLEO. I have downloaded the C example code. Setup the SPI and the Interrupt pin using STM32CubeMX. With the help of some example code i hooked it all up. 

I get correct value for WHO_AM_I (0Fh) register. 

This is what i get on the logical analyzer. First one is the temperature and the second one is the air pressure. 

I get 43.06 degC and air pressure of about 1027 hPa which puts me -120m underground. I am quite sure i am not underground and it is not 43 deg.  

After reset I am using the default settings 10hz, BDU bit set. No change from the example.

What i have noticed is that when i apply heat to the sensor the air pressure goes down, while the temperature is more or less the same. Any advice? What have i missed? Magic spell, as long as it does the trick? 

Cheers!##

[Miroslav BATEK]

Posted on April 04, 2018 at 16:34

Concerning the pressure the local air pressure changes with the weather, so 1027 hPa doesn't have to mean you are 120 meters underground. To calculate the altitude you have to use you local air pressure which you will get from your local weather station.

Concerning the temperature, isn't the sensor located close to some voltage regulator or other parts which can generate heat? 

[Dimitar Dyakov]

Posted on April 04, 2018 at 16:50

Hello Miroslav,

I have a Digifly Archimede variometer that reads 970hPa (constitutes for 550m-600m which is more or less correct), while the LPS33HW is around 1027hPa put side by side. There is no heat source near the board as well. The sensor is elevated from the nucleo by the adapter board as well. 

This does not explain when I apply heat the sensor why the barometric reading goes down and the temperature stays the same. 

May be it is time to get another sensor?Best regards,Dimitar

[Miroslav BATEK]

Posted on April 05, 2018 at 12:47

Is the sensor soldered on your own board or are you using the STEVAL-MKI183V1 DIL24 adapter?

If it is your own board can you share the schematic?

Anyway, the sensor seems to be strange. If possible, can you use different piece?

I have to highlight that ST doesn't specify the temperature measurement accuracy fro LPS33HW so the error can be quite high, but If I suppose your ambient temperature is around 25°C the error is too high in your case.

[Dimitar Dyakov]

Posted on April 05, 2018 at 16:31

I will order another one and see what happens next. 

[Dimitar Dyakov]

Posted on April 22, 2018 at 17:18

Just changed the sensor and it works. A bit strange especially on a demo board. It is all good when it ends good right