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
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I am a recently retired ST Employee. My former username was John E KVAM.
