VL6180X wrap-around filtering: is this possible without the API?

[RichardR]

Hello,

I'm working on a project with a VL6180X ranging sensor, and I'm running into the problem that it responds to reflective surfaces far beyond the desired range (100 mm) - e.g. it picks up reflective stripes on the jackets of emergency personnel at over 1200 mm (4 feet) distance, rendering the whole thing unusable.

The datasheet mentions a Wrap-Around Filter (WAF) to solve this problem; however, it turns out that this filter (and only this filter) requires the use of the VL6180X API - which is a problem, as I'm using a simple PIC controller for the overall functionality (switching on a small liquid pump when a hand is within range).

I already checked out the API, but it isn't clear at all how this WAF works. Could someone shed some light on this? If it is merely a matter of setting a bunch of registers, my controller should be able to handle that just fine; and even if some continuous external processing is required, it shouldn't be impossible.

(I also looked if I could simply decrease the VCSEL output to limit the range, but there seems to be no register setting for this.)

What I don't want, is to redesign and rebuild the hardware and software in order to be able to use just this one feature.

Thanks already for any help!

Richard

[John E KVAM]

Another contact states he has seen a similar problem. System only failed in the white version of the product. Customer never found a solution. They chose to reset the sensor regularly. Bummer.

[RichardR]

Hello John,

Thank you for all the extra information, and in a way it is good to know that others have experienced some trouble with bright environments as well. We'll think about implementing a reset option.

The sensors have a dedicated 2.8V LDO power supply with generous local decoupling using several different ceramic capacitors. The I2C runs at a leisurely 100 kHz, albeit over several inches of flatcable, which may pick up occasional EMC.

About resetting the device: all controller pins are in use already, but I can implement a simple reset circuit using SCL with a high-impedance RC circuit and a Schmitt-Trigger buffer, to generate a low reset on GPIO0 if SCL is forced low for e.g. 100 ms (as SCL is high 99.9% of the time during normal operation).

As I already mentioned, the latest tests are encouraging in that we haven't experienced any problems lately. Testing & close monitoring continues in the next few weeks, and if we still get no spurious readings, I think we can safely put the system in production -- maybe with the extra reset circuitry, to be on the safe side.

Thanks once again, best regards,

Richard