VL53L4cd not able to detect dark surface

[pthakkar]

I am trying to use VL53L4CD to detect whether there is a car on top of the sensor or not...I am placing my sensor on the ground and trying to detect if a car is parked on top of the sensor. But it is not able to detect the cars bottom surface. However if I place any other object it is able to detect that....

Is this the right sensor for this application?

[AScha.3]

For detecting a car usually inductive sensors are used, something like a big wire loop in the ground.

Optical sensor on the ground is a bad idea, just imagine some drops of black oil dropping down...

[pthakkar]

Oil spillage and things have been taken care of. Only issue is that the sensor is not able to detect the car when it is on top..

[AlexCloned]

Hello. No, it is not possible for an L4 not being able to detect a target
at ~40 cm.

[Andrew Neil]

I'm with @AScha.3 - an optical sensor is not the usual way to detect presence of a car, and doesn't sound like a particularly good way to do it.

Anyhow ...

 

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In the title, @pthakkar wrote:

VL53L4cd not able to detect dark surface?

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How do you know it's specifically "dark surface" that's causing the problem?

Some parts under a car can be shiny.

Also, the underside of a car is not a simple, flat surface...

 

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@pthakkar wrote:

 it is not able to detect the cars bottom surface. 

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How many cars have you tried?

Have you tried the cars in multiple positions?

 

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@pthakkar wrote:

if I place any other object it is able to detect that.

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any other object?

What objects have you tried?

[John_Kvam]

The Time-of-Flight sensors work by shooting out a flash of photons and measuring how long until they return. So, it stands to reason that dark, non-reflective surfaces are going to be problematic. 

(For reference, white printer paper is 88% reflective, a matte finish black spray paint is 5% reflective.)

Now the underside of many modern car engine bays are covered by a black plastic shield, that is light, durable and helps with aerodynamics.  And that is probably your worst case. And to make matters worse, plastic is somewhat transparent to 940nm light. 

But ST did a pretty fair job of testing when it claimed the sensor could 'see' 1.2M. But the test assumed an 88% target.

But they also assumed some other testing parameters. 

In the datasheet, they claim between 450 and 475mm at 17% - which is a medium dark gray. This is not a bad specification. There are not very many targets darker than that. Although it appears you might have found one. Especially when that shield collects a lot of oil drips and road tar. 

They also used a 33ms range in the test - indoors. 

Now let's assume there is not much sunlight under the car body. So maybe the indoor number is not so bad an estimate. 

But you've clearly done the test. And it appears to have failed to meet your expectations.

You could try a longer timing budget. With more time to find photons, you might get a better result. 

Or you could switch to the VL53L1X - with its lens that gathers more light it really does range farther. 

But that lens costs money, and so it's more expensive. 

And there is always 'the next sensor' which will be better of course. But you might have to wait a long time for that. 

- john