VL53L3CD Auto Calibration for scaling?

[will3]

We use the VL53L4CD TOF inside a container which is either 390mm long or 260mm long. 

Our current process during manufacturing/testing is to perform the calibration procedure either using 390 or 260 depending on the container length. This is a manual process.

I am looking for a way to automate this.  A way for the device to auto calibrate and auto determine its own length.  Or,  at the end of the day,  we are only interested in the delta between tof readings (items are placed into containers) and only need the 390 or 260 in order to calibrate so we can get an accurate delta.

I gotta believe I am not the first to have this issue? The calibration procedure having to “know” the length creates issues in terms of manufacturing hundreds or thousands of bin.  Slows it all down.

Any idea?

Thanks,

Will

 

[John_Kvam]

Will - I spend some 10 years working on these sensors before I retired last year and I always loved these kinds of questions. 

I think I might come up with something. 

Let’s try this. 

The crosstalk is 100% dependent on the coverglass. And if your coverglass is consistent, you can test a few the hard way and then use that number for your entire production run, only checking periodically to insure your production values are still the same. 

But offset is NOT consistent - it changes chip to chip. However, you only have two possibilities - and they are 13 cm apart. 

Create your software so it downloads the known crosstalk values, and upon first boot it does the RefSPAD call and maybe 20 or 30 ranges. Average those results and decide if you are closer to 390 or 260. That is your offset. Store it in ROM somewhere and apply that after every range. Or you can put the offset into the chip at every bootup.

If your container is clear, you’d be better off doing the initial boot over a white target so you get a good reflection. 

good luck - 

• john