VL6180X Range Offset Change issue

[ishikawa]

Posted on February 01, 2017 at 09:47

Hi, all

I'm using some VL6180X devices on my custom board.

Then, their range offset seem to change every start up about �5mm, although I adjust the offset as directed in application note.What affects the range offset?Under normal circumstances, is it enough with only once adjustment?Is this problem specific to my board?

Does anyone has the same issue?

Best regards,

Ishikawa#proximity-sensor #multiple-vl6180x #offset #vl6180

[John E KVAM]

Posted on April 07, 2017 at 18:41

The offset data is NOT stored within the sensor. The procedure should be:

• Follow the offset calibration procedure and get the offset result.
• Save that offset result in your CPU's memory. 
• At every restart, reprogram the offset register.

[ishikawa]

Posted on April 21, 2017 at 23:46

Hi, john

Thank you for your response and I apologize my late reply.

Please let me ask you a question about the following:

>The offset data is NOT stored within the sensor.

There are the following codes in this document (

http://www.st.com/content/ccc/resource/technical/document/datasheet/c4/11/28/86/e6/26/44/b3/DM00112632.pdf/files/DM00112632.pdf/jcr:content/translations/en.DM00112632.pdf

 ).

>The part-to-part range offset is calibrated during manufacture and stored in NVM.

Isn't the offset value hold in the VL6180's NVM?

According to this document(

https://my.st.com/content/ccc/resource/technical/document/user_manual/group0/ba/47/75/5e/d2/80/47/7e/DM00247018/files/DM00247018.pdf/jcr:content/translations/en.DM00247018.pdf

 ), 

VL6180 has a NVM.

Best regards

Ishikawa

[ishikawa]

Posted on April 22, 2017 at 00:41

Hi, John

Please let me ask you a question again.

>I'm using some VL6180X devices on my custom board.

Then, their range offset seem to change every start up about ±5mm, although I adjust the offset as directed in application note.

>What affects the range offset?

Now, I compensate the range data like following:

1.turn on my board

2.put a white board in front of the sensor at 50mm

3.get the range data many times

4.calculate the offset in accordance with procedure of application note 4.1.1

https://cdn.sparkfun.com/datasheets/Sensors/Proximity/VL6180_ApplicationNote.pdf

 

At present, I repeat this procedure every restart.

However, this is very very bothersome.

Once, I intended to reuse the offset data by saving the data in my file,

but when I restarted my board, the offset data seemed to be inappropriate.

Can I reuse the offset data, if I restart the board?

Best reagrds

Ishikawa

[John E KVAM]

Posted on January 02, 2018 at 20:21

Once you do the offset calibration, it's good for that chip forever. Do the calibration, read the cal data from the chip and store it in your application. At reboot, write the cal data you saved to the sensor.