How to choose a Time-of-Flight sensor?
1. Introduction
There are getting to be many Time-of-Flight sensors, and although there is a product selection page at www.ST.com/TimeOfFlight it can be a bit of a challenge.
So let me introduce each sensor grouping them by their most significant attributes. Then we can get into more detail. To make things more concise, the terms are defined below the sensor listing
2. Time-of-Flight sensors performances
2.1 Short distance*; lowest power; 850nm VCSEL*; Autonomous
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VL6180V1
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VL6180CX – same as the VL6180V1, but adds ALS*
All the VL53 sensors below have invisible, 940nm VCSELs
2.2 Medium distance sensors
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VL53L0CX – Autonomous; 27-degree Field of View*
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VL53L4CD* – Autonomous 17-degree Field of View; Ultra Lite software (ULD) *
2.3 Longer distance sensors
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VL53L1CX – Adds an optical* lens to the L0 to get longer ranging, ULD driver
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VL53L3CX – Adds Histograms* to get longer ranging
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VL53L4CX –Single Mode 17-degree Field of View; Histograms
2.4 The longest range
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VL53L1CB – Adds optical lens AND Histograms to get the very longest range.
Up to this point the effort has been to ever longer distance sensors. But we’ve reached the practical limit. So here is a completely new class of device:
2.5 Multi-zone:
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VL53L5CX – Long distance; Multi-zone; Wide Field of View*; Autonomous
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The ‘L5CX’ is really in a class by itself, it is much more capable than then the prior sensors.
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3. Summary Table
4. Glossary
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Distance – Datasheet gives the max distance in ideal conditions, but here is a practical estimate:
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Short distance – good for seeing hands to 50cm
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Medium distance – can see people to 1.5M
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Long distance – Can see people to 3M
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Longer distance – Can see farther, but one needs a big target.
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VCSEL – Vertical Cavity Surface Emitting Laser. 850nm is barely visible, All the VL53 sensors use a completely invisible 940nm VCSEL.
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Field of View (FoV) – most sensors have a 27-degree Field of View. This means the diameter of the area of illumination is ½ the distance to the target.
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L4CX has a 17-degree FoV.
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L5CX has a square FoV of 45x45 for 63° diagonal
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Autonomous – sensor does all the work. It can wake a sleeping MCU based on proximity.
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ULD – Ultra Lite Driver. Software available for the very smallest MCUs.
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ALS – Ambient Light Sensor. Not very many people use this, but they can.
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Optics – by adding a Lens on the sensor it can gather more light and can range farter. It can also adjust the Region of Interest.
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Histograms – Patented algorithm: each bin of the histogram is the number of photons captured during that clock cycle. This allows multiple targets in one collect, better accuracy and longer distances. However, the processing of the histogram is done in the host with ST software.
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Single Mode VCSEL – narrower FoV laser that comes on more quickly and thus produces a bit more accuracy.
