Interleave mode, register 0x5F, interrupt on QVAR value?

[KWine]

In AN5755 it says: "If the user wants to read both pressure and Qvar, the interleaved mode should be enabled with bit QVAR_AUTO_EN in register 12h: • write(0x12, 0xA0); // QVAR_enable in interleaved mode In this mode the output registers are filled once with pressure data and once with Qvar data alternatively every ODR. So, both pressure and Qvar data have their ODR halved (in one-shot mode the output is filled one time with pressure, one time with Qvar)."

I don't see QVAR_AUTO_EN in the CTRL_REG3 data sheet description, and when I tried this it didn't seem to work. Is this supported/further documented?

In order to minimize power in barometer mode the data sheet advises to write 0x00 to register 0x5F. But this register is not indicated in the register map. I did this and nothing bad happened, but again, is this supported/documented somewhere?

Lastly, I would like to be able to set an over value interrupt on one of the INT pins for a QVAR value measured on the other INT (AH) pin. This seems to be possible with the LSM6DSV. Is it possible with the ILPS22QS and is "how to" documented somewhere?

Btw, QVAR works well on my ILPS22QS breakout, but I see a persistent 1.5 mV offset even though I have an offset cancelling circuit (I am using 1% 9.1 MOhm resistors). Any idea what I could be doing wrong?

Thanks for your help.

[Eleon BORLINI]

Hi @KWine​ ,

first, thank you for your article on Github, I'll promote it on the community, if you agree.

I just checked your questions with our QVar experts:

For point 1, the interleaved mode: we have to better double check, probably the app note is missing a command to enable the interleaved mode. I'll let you know asap once the revision of the app note will be published.

For point 2, regarding the 0x05 register, you are right that is is not mentioned in the current version of the datasheet, since it is (also) an OTP register (and cannot be over-write in the standard way). Did the power consumption drop afterwards?

For point 3, unfortunately the pressure sensor ILPS22QS doesn't allow the Interrupt management a in the DSV case, mainly due to internal different logic.

For point 4: the offset could be caused by a series of internal misalignments. It is not so high in our experience, but it might be minimized by fine-tuning the external resistors. Are you using the suggested polarization circuit? If so, you can fine-change the resistors to get a 0V output.

 

-Eleon

[KWine · Accepted solution]

Hi Eleon,

Thanks for the rapid reply!

Yes, I am using such a polarization circuit with 1% 9.1 MOhm resistors. Yesterday I thought I measured ~1 MOhm resistance across my flex electrode, which would explain the extra offset; today I don't. But I take your point, in the circuit i could adjust the resistance to zero out any offset. In any case, the offset is < 10% of the full scale QVAR reading so doesn't affect detection of touches etc.

I look forward to learning more about the QVAR disable and interleave mode, thanks for looking into this. I didn't test the power consumption yet but I will. I would like to understand everything in the application note and data sheet before I do.

You may refer to or otherwise use the github material any way you like, it is intended to be open source. I have similar "writeups" for the LIS2DW12 and other ST sensors as well as other manu's sensors (I know you don't want to feature these!).

I am looking forward to seeing the revision of the datasheet/app note.

One thing I might suggest. The AN electrode design is fine for touch and tap detection. But QVAR should be capable of graded sensing, that is, using some kind of electrode to detect position of a finger, say, sliding along an electrode strip such that the position from 0 mm to 100 mm, say, might be represented by a QVAR value of 0 mV to 18 mV, respectively. Can the QVAR experts suggest what kind of electrode design might accomplish this linear transducer function?

edit: Is there some way I could obtain samples of the LSM6DSV16X for testing? I don't see this for sale anywhere...

Thanks again for your help!

Kris

[Eleon BORLINI]

Hi Kris @KWine​ ,

we should release a new version of the AN in the following weeks, that will explain better the capabilities of the Qvar and the related configurations. And for this:

>> Is there some way I could obtain samples of the LSM6DSV16X for testing? I don't see this for sale anywhere...

Also these samples will be available soon, we are currently completing the qualification phases.

I'll keep you updated, and if you want you can keep us updated about your tests.

Thank you again for your knowledge sharing!

-Eleon