Strange behavior with VL53L1X between transparent and reflective objects

[Nick Wilke]

I was testing the returns from the VL53L1X to build up an algorithm for a project, and one of the edge cases is an object outside of a transparent 'wall'. Normally, when there is an object outside of the transparent 'wall', the sensor picks up the object with a slightly lower signal strength than usual. However, when I did it with a reflective object (sheet metal, mostly), the shape of the object seems to be projected where the glass is. Even with a cylinder of sheet metal, the sensor returns that there is a cylindrical shape of points where the (flat) transparent wall is.

It's fortunately very good for me for this to behave in this way, but I'd like to see if I can confirm that this is a reasonable return, and not just a lucky scenario.

[John E KVAM]

​There is lots of stuff going on here.

1) Transparent to you is not necessarily transparent at 940nm. Plane glass is transparent, Low-E glass is not. And most plastic is transparent to 940nm, no matter what color it is.

2) Even the clearest glass is only 95% transparent.  I'm guessing that's your slightly lower signal than usual.

I don' t quite understand what you are doing, but I'm sure your result is not 'lucky'. But you might get varied results with different test scenarios - like dirty glass. So do check that. 

Keep in mind ALL the photons are averaged. So with a really  bright target like sheet metal that will dominate. With a darker target, the glass will start to influence the average and you will get a different number.

And I'd worry about photons hitting a curved mirror-like surface. Those photons will bounce off and not be detect at all.