Student capstone: VL53L1X vs VL53L5CX for drop-off detection on a wearable aid for blind users

[sparta2900]

Student capstone: VL53L1X vs VL53L5CX for drop-off detection on a wearable aid for blind users

Hi ST team,

I'm an Electrical Engineering student at BCIT in Vancouver, and my capstone team is building a wearable obstacle detection aid for blind users. A chest-mounted depth camera handles obstacles, and we want dedicated ToF sensors for drop-offs like stairs going down. The sensors would be mounted at chest or waist height, angled down at the floor about 1.5 m ahead of the user, and read over I2C by an ESP32 so drop-off warnings don't depend on the main processor.

We're still deciding between 2 to 3 VL53L1X single-point sensors and one VL53L5CX, and would really appreciate a quick recommendation. Our main concerns:

- Measuring the floor at a shallow angle from about 2 m away. Which part handles that geometry more reliably, and what would you suggest for field of view or ROI settings?
- Dark, glossy, or polished floors (tile, vinyl, gym floors) that may return a weak or specular signal.
- Readings while the sensor bobs and tilts with walking. What ranging frequency and timing budget would you start with to catch a drop-off quickly without many false alarms?

We'd also be glad to share the project with the ST Community once it's working. If ST offers samples or evaluation boards for student projects, we'd be grateful to hear about it, but your advice alone would help a lot.

Thanks,
 

[John_Kvam]

The best low cost solution would be the VL53L8CX - newer than the L5 and better in every way. Same price. 

(better than 2 L1’s. Fewer parts. Price not that much different.)

Your issues are going to be:

1) direct sunlight. The sun’s energy can completely swamp the sensor. Perhaps you could warn the user when this is the situation. The sensor will know when the ambient light is preventing a detection, But cannot do anything about it. 

2. light hitting a specular (mirror-like) surface will bounce away. With no return signal the sensor cannot ‘see’ the floor. The sensor can tell there is no return signal, but can’t say anything else.

Find a way to warn the user, and you will have a product.

[sparta2900]

Thanks John, really helpful. I hadn't looked at the VL53L8CX, and it looks like an easy swap from the L5CX.

One detail I should have mentioned: we're only designing and testing for indoor use (hallways, classrooms, stairwells). Does that change your recommendation? With sunlight mostly out of the picture, is the L8CX still the better pick over the L5CX, or are glossy floors the main thing to worry about?

Thanks again,

[Andrew Neil]

With sunlight mostly out of the picture,

I don’t think you’ll get away with that if this is intended to be a real product.

But OK if just for a student exercise, and the limitations are clearly discussed in your write-up

[John_Kvam]

The L8 fixes a few issues with the L5, along with adding some features, so yes, it’s the best choice.

Specifying an indoor sensor will take care of the ambient issue, but really polished floors - think marble - are still going to be an issue - unless you have a grout line to work with. You might also have problems with a really, really black non-wool rug - but I don’t imagine these are common. 

the L8 has a 45 degree field of view, so if you point the sensor at  45 degrees below horizontal, even the steepest light is going to hit the floor and bounce away if the floor is a perfect mirror. Luckily, most floors are NOT perfect mirrors, but it is a possibility you have to think about. Pointing out at 65 degress below horizontal will find the floor, but one gives up a lot of straight-ahead view.  

When I was contemplating the blind user case, I always thought a sensor in a belt buckle might be a way to go. One could put a pretty large battery on a belt, and one generally walks in the same direction as one’s hips are pointed. I figured the belt could vibrate with the distance to an object, vibrating a lot if something were close - of if there were a drop-off. 

I do wish you luck with this. It would be a great help.

• john