histograms with two peaks when detecting a single target

旭王.1 · ‎2021-11-18

We are using VL53L3CX evaluation board to dig out some information from the histogram.

The 24-bin histogram are retreived by calling the Get_AdditionalData function. Two consecutive sets of histograms are got, when we use a white wall as target and the distance between EVM and the wall is 70cm. As shown below, there are two peaks in each consecutive histograms, which make me confused. Is it reasonable to get histograms just like these? Or I got something wrong on retreiving data?

Many thanks,

XM

John E KVAM · ‎2021-11-19

in very approximate terms each bin is worth 20cm. So at 70cm you would expect no data in bins 0, 1, and 2, a half portion in bin 3 and a full bin 4.

So the shape of your histogram looks right.

So now to your issue with the two 'lumps'.

To detect radar aliasing (which you can google) we do 2 ranges - an A and a B range. And report back after each 'half'.

And they have different pulse repetition timings.

So one range has 4 extra bins in it. (One has 20 bins, the other 24 bins)

But we want to maximize the use of data.

So the first 4 bins of the short one of the ranges is AMBIENT and not distance data.

If you take either the even ranges or the odd ranges they will be consistent.

Or if you remove the first 4 ambient data points the evens will line up with the odds.

I have carefully left out which is the short one with ambient, and which is the long one without ambient. Because I always forget.

But look at the data. It will be obvious.

I don't think the chip designers never planned on the histograms being so useful to people. So they didn't make it as easy as they could have.

john

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旭王.1 · ‎2021-11-21

Thanks, that's very helpful.

A further question is when we measured some unique distances, the even or odd histograms show "probably" two peaks but not so complete.

For example as plotted below, when the distance is 1100mm, two clear separate "peaks" appear in the odd histogram (left blue), but for the even one (right red) the peak number seems to be three? I guess through some repartition operation, these three peaks shall be recombined into two, but I don't know the detailed principle and the hiden reasons.

Could you please lead me some clue?

Many thanks,

XM