Using ToF sensor to measure distance to small object

[pasikav]

Hello,

Basically i am trying to measure distance to a hand that moves above the sensor, returned distance is used to light leds approximately at hand height.

My problem is that hand is probably to small object or its reflectivity is not enough that above 1 meter with VL53l1x and above 1,7m at best with VL53l3x the hand disappears and i am out of ideas how or if even is it possible to improve range so i can detect the hand over 2m distance.

there will eventually be mirrors behind the hand, but at this point I don't think it will affect the results.

Any ideas that can help me with this project??

Best regards!

[John E KVAM · Accepted solution]

Your hand is about 50% reflective. This means that about half of the photons that hit it will reflect.

The sensor requires a certain number of photons in order to 'see' something. We would like a return rate of 20million photons per second but can get by with 0.5Million.

The number of photons returned goes down as a square of the distance. So at 10cm we have so many photons we actually turn off a lot of the photon detectors. At about 70cm most of our sensors can no longer see your hand. 

But that leaves the VL53L8CX. This is a multizone sensor. It divides up the 45x45 degree field of view into 64 zones, each about 5x5 degrees. At 2meters, one's hand occupies about 1/2 of a zone

But the L8 (along with the VL53L1CB, the VL53L4CX and the VL53L3CX) uses histograms. And with histograms one can differentiate between 2 targets with some distance between them. 

So if your hand were at 1M, and the ceiling above were 1 meter beyond that, the sensor would not mix those targets together. 

The VL53L8CX also has a more powerful VCSEL - giving you a bit more range. 

It's my belief that you really need the VL53L8CX to solve this problem. I'd invest in the P-Nucleo-53L8A1 and give it a try. You are kind of at the limits of what the sensors can do. 

- john