Self test for vl53l8cxv0gc/1

[Jagannathan]

Hi,

Currently, we are testing vl53l8cxv0gc/1 by placing an object in front and moving it and reading the values. 

Is there a way to test the functionality of vl53l8cxv0gc/1 in a production environment? Is there a self test mechanism for this sensor?

Thanks,

Jagan

[John_Kvam]

During production we encourage doing a crosstalk calibration. This process measures the number of photons that return immediately from the coverglass. Knowing this number, we can adjust the results that are between 0 and 70cm or so. (If you have a crosstalk-free coverglass or none at all you can skip this calibration.) 

Oddly the calibration involves just ranging on nothing. And if nothing is hard to produce you can range on a target that is 80cm away (or more) and is not very reflective. 

Then you store the crosstalk results away and use them whenever you boot up.

If you used this crosstalk calibration as a production self-test, you would be all set. You should get similar numbers to all your other units, and if you didn't, you would know something was wrong. 

In this way, you not only test the sensor, but you test the cleanliness of the coverglass as well. 

But it's possible that you want to test PRIOR to final assembly - before the coverglass is on. 

In this case, I'd just point the sensor as something constant. A ceiling would do it, or a wall - depending on which way is easiest. You should get 64 distances and 64 signal rates, and all your units should get the same thing within +/- 3%.

However, your method of, "placing an object in front and moving it and reading the values", is not wrong, but you could also get some measure of accuracy if you placed a target of known distance in front of the sensor. 

[Jagannathan]

Hi John,

Thanks for your suggestion.

In our case, we do not assemble the boards ourselves — the assembly process is handled by our customer.

During our testing, we will not be removing the protective film. It will only be removed during the customer’s assembly process to ensure the ToF sensor surface remains dust-free and to avoid adding an additional step for the production team. We are also concerned that the protective film could be misplaced if removed during testing.

Therefore, we are exploring a way to perform this test with minimal or no fixtures.

Looking forward to your suggestions.

Thanks,
Jagan

[John_Kvam]

The I have an idea. A customer of mine forgot to remove the tape and was complaining about really bad crosstalk. (It was actually a hard problem to find as he had fully assembled his units.)

But let's use this to your advantage. With the board built and the tape on, simply run the crosstalk test. And expect it to be bad. But if you are getting bad crosstalk, you know the sensor booted, the laser fired, the photons were received, and your sensor can send the results back to the MCU. And that is about everything the sensor can do. 

As long as your results for any one unit look about like all the others, you can be assured that the sensor works. 

Using the p-nucleo-53l8A1 eval kit, you can get a good idea of what the numbers should look like. 

And all you have to do is be a little careful not to put anything in the sensor's field of view for 80cm. 

- john