Hi ayeiser,
That's an excellent question, and a very common and frustrating challenge with Time-of-Flight (ToF) sensors in industrial and robotics environments. You've hit on the core problem: retroreflective surfaces return an overwhelming signal that saturates the sensor's SPAD array, effectively "blinding" it.
Unfortunately, it's not possible to directly adjust the VCSEL (laser) power level on the VL53L7CX like you can with some other sensors. ST pre-configures the laser power in the firmware to ensure it remains "eye-safe" and compliant with safety regulations, so this isn't a tunable parameter for the end user.
Based on my experience with these sensors, the key to handling retroreflective surfaces lies in how you process the data and tune the sharpener parameter. Here are two main approaches you can consider, depending on your application's priority:
Approach A: Prioritizing the Retroreflective Object
This method is useful if the retroreflective object itself is your primary target.
Set the sharpener to 0%. This will cause the sensor to return a similar distance for most or all zones, with a large number of zones being blinded by the retroreflector, as you've observed.
Utilize the number of targets feature. By setting the sensor to report two targets, you might be able to find a second target that corresponds to the background or other objects. Your software would then need to identify and use this secondary target's data.
Approach B: Prioritizing the Background and Context
If you're more interested in seeing the world around the retroreflector, this is the recommended approach.
Increase the sharpener value to more than 5%. By raising this value, you are telling the sensor to be more selective about what it considers a valid return signal. This helps the sensor differentiate between the overwhelming retroreflective signal and the weaker signals from the background. If it is possible for the sensor to still detect de context and background you will get it this way.
Accept measurement errors. With this method, you will likely see a significant number of zones immediately surrounding the retroreflector report an error. However, this trade-off is often acceptable as it allows the rest of the array to provide accurate distance data for the background and other objects.
While these approaches are good starting points, the best solution will depend on your specific environment and how your application needs to react to these surfaces. It's often a matter of trial and error to find the optimal sharpener value for your use case.
I have not personally tried initializing the VL53L7CX with the firmware from the VL53L5CX to reduce laser power, but I think it would be an interesting idea to be discussed. Given that the L7CX uses a wider angle and may need more power to achieve its advertised range, it's possible the L5CX firmware would indeed use a lower power setting. I'm taking into account that an L7CX is in essence an L5 with different optics. However, I would be hesitant to recommend this without an official response from an ST engineer, as it could lead to unexpected behavior.
I've attached a few images from a test I ran to illustrate these points. I used a VL53L8CX sensor because I had the evaluation board on hand, but the principles are the same for the L7CX. The "Scene" image shows my test setup: a primary target at 1m, with other objects up to 1.2m, and a background around 2m. The "Approach_A" image demonstrates how the first strategy looks, while the "Approach_B" and "Approach_B_variant" images show the second strategy with two different sharpener levels. The retroreflective is 10 cm by 10 cm. I hope these visuals are helpful!
Scene:
Approach_B_variant
Approach_A
Approach_B
