VL53L5CX:What does Status 6 mean.

[Sidlauskas.David]

More specifically, the doc's say status 6 means "wrap around not performed". What is wrap around? Is this a bad condition?

Thanks,

Dave

[John E KVAM · Accepted solution]

Google Radar Aliasing.

An error 6 is not bad, and generally it's not likely. But it's a warning that a check we generally do is not done on the first range.

IN order to detect something called Radar Aliasing, one needs to do 2 separate ranges with different pulse intervals..

But that takes more time.

So the sensor does one range - and returns the value with a waring that no aliasing check was done.

The next range is then done with the alternate pulse interval and the Aliasing check is done by comparing the result to the previous range information.

[ABesp.1]

Does the range status 7 (VL53LX_RANGESTATUS_WRAP_TARGET_FAIL) mean that range aliasing has been detected?

[John E KVAM]

it would have been easier for me if all the error numbers were the same for all our sensors. So in one sensor the 'Wrap Fail' is a number 6, but in some other sensor it's some other number. But the term Wrap Fail is used in all the chips to suggest to the user that aliasing has been detected.

But it's not always correct.

A Wrap Fail is declared when a range with one pulse repetition rate differs from the very next range with a different pulse repetition rate. And if your target is relatively stable, this system works. But if you have rapid motion the range at time N will be different from the range at time N+1. So we report 'Wrap Fail', but in fact both ranges were right - the target just moved.

So I'd treat this 'error' more as a warning. If you know something about your system - like rapid motion is typical - then go ahead and use the number.

Generally near targets have a large signal - and that signal strength goes down as as square of the distance. So if you get a Wrap Fail warning, and the signal is strong, one might assume it was motion and not a true wrap fail.

• john

[ABesp.1]

Interesting, just to get it right, do you mean two consecutive ranges within two consecutive clock cycles or timing budgets by N and N+1? Also beyond which speed may the system be no longer regarded as stable in order to check for abnormal wrap fail?

By the way, the question is related to VL53L3CX.

[John E KVAM]

The VL53L3CX has some software tweaks that our other sensors do not. Prior sensors did 2 separate ranges and reported the result. So there was no '6' warning. The L3 sped up it's reporting by reporting every 'half' range. Both are valid, but taken together, they can detect radar aliasing.

Signal strengths are pretty consistent if you use 'normal' targets. We call these 'Lambertian' surfaces. As they get farther away the signal return drops as a square of the distance. So a hand at 10 cm returns a good strong signal, but a wall at some 5 meters will return a much lower signal even though it's much larger.

But then there are specular surfaces - basically mirrors. The signal will remain strong for a goodly long distance and this is where radar aliasing (wrap around) can give you issues. But the mirror has to be pretty perpendicular to the sensor to be a problem. However the retro-reflective tape used on safety vests is amazingly reflective at very wide angles and give you fits. Or if you want to identify some object at a really long distance you can use a spot of this stuff.

But it takes some testing on your part to really know what's going on in your application.

• john