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Ralph Yamamoto's Blog VL6180X TOF Sensor Repaired
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Engagement
  • Author Author: ralphjy
  • Date Created: 19 May 2020 4:02 AM Date Created
  • Views 334 views
  • Likes 2 likes
  • Comments 1 comment
  • i2c translators
  • bss138 mosfet
  • vl6180x
Related
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VL6180X TOF Sensor Repaired

ralphjy
ralphjy
19 May 2020

About a month ago I encountered a broken VL6180X TOF sensor board that I was trying to use for my laser focusing project Laser Focus Assembly Completed.

 

The sensor wasn't even responding to I2C address queries which prompted me seek some help from the community Any known I2C issues with VL6180X TOF sensor.  Gough Lui suggested that it was likely to be in the level translators for the SCL and SDA signals.  The sensor itself runs on 2.8V from a local regulator but the I2C pins can interface to 3.3V or 5V levels set by the VIN pin.

image

Because this was a new purchase I decided to contact the seller rather than spending time to troubleshoot and possibly repair the board.  The seller responded quickly and after going through some basic tests sent me a replacement board which worked.  The seller did not want me to return the defective board.

 

After finishing my project I decided it would be worth taking a quick look at the defective board before throwing it away.  I ran an I2C scanner program on an Arduino Uno and looked at the I2C signals before and after the translators.

 

Here are the signal at the input:

image

 

Here is the SCL signal before and after the translator 5V->2.8V:

image

 

Here is the SDA signal after the translator referenced to the SCL input:

image

 

It was fairly obvious that the SDA translator was broken.  I had done a visual inspection of the board before to look for bad solder joints or shorts and nothing was apparent.  I had used a DVM to check for shorts and continuity.

 

Here is a close up view of the defective board:

image

 

A close look at the level translators.  SCL is on the left and SDA is on the right.

image

 

I noticed that the MOSFET in the SDA circuit appeared to have a crack in the body.  I went to desolder the MOSFET and the body came off in two pieces so it definitely had been damaged in assembly.  I guess these boards aren't tested post assembly.  I don't keep a supply of SMD parts on hand and had to order a new BSS138 part which arrived today.

 

I replaced the part and ran a quick ranging test from 6 inches to 2 inches (measurements in mm).  Everything worked!! image

19:48:42.286 -> 147.80

19:48:43.288 -> 137.11

19:48:44.320 -> 119.14

19:48:45.316 -> 108.67

19:48:46.351 -> 98.19

19:48:47.352 -> 97.62

19:48:48.386 -> 86.70

19:48:49.382 -> 87.27

19:48:50.407 -> 86.92

19:48:51.440 -> 85.16

19:48:52.469 -> 76.69

19:48:53.465 -> 76.47

19:48:54.499 -> 66.81

19:48:55.500 -> 65.58

19:48:56.534 -> 53.23

19:48:57.528 -> 54.21

19:48:58.559 -> 53.51

19:48:59.593 -> 52.52

 

I now have a spare short range TOF sensor.

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  • Gough Lui
    Gough Lui over 3 years ago

    Good work - that's one less wasted item! Seems like those FETs are pretty popular for level translation tasks, so it's probably not a bad thing to have a few spares kicking about.

     

    - Gough

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