[Animats]

Now that's a nice device, and is a true time of flight sensor. There's a similar model with 1.2m range.[1] Don't know whether it's a pulse LIDAR or an RF-modulated beam. The ones that use a pulse laser can have much more range and can work outdoors. They must far outshine the sun, but only at one wavelength and only for a nanosecond. That's quite possible.

[1] https://www.adafruit.com/product/3317

[antoinealb]

According to the VL53L0X datasheet:

> During the ranging operation, several VCSEL infrared pulses are emitted, then reflected back by the target object, and detected by the receiving array.

VCSEL is Vertical cavity surface emitting laser. Therefore I would say a pulse laser.

[fest]

That one detects phase difference of the reflected signal.

[Groxx]

>The VL6180X can detect the "time of flight", or how long the laser light has taken to bounce back to the sensor.

Sounds like no?

[fest]

I am suspicious about this statement for the following reasons:

* Some ST patents [0] say they are doing time of flight but have actually came up with slight variation on reflected signal phase shift measurement (see reply by Animats).

* Seeing internal API functions like this [1] in APIs they provide for sensors of this family. Of course, this might be something else (e.g. phase shift of internal PLLs/whatever).

* The shortest time in which this sensor performs measurement is on the order of few tens of milliseconds, and the high accuracy modes take up to 100ms. True time-of-flight systems (e.g. [2]) should have the answer ready on the order of nanoseconds (for the distances this sensor works at) and I haven't yet seen designs where there is so significant post-processing of the data which could explain this latency.

Don't take me wrong, I've worked with VL6180X and VL53L0X (and look forward to work with VL53L1X), and these sensors are the best in this size but I'm just suspicious that they are directly measuring time for the signal to bounce back, but are instead inferring the time based on some other measurements.

Actually, this made me think that I probably have photodiodes with wide enough bandwidth laying around so I could check the transmitted signal on oscilloscope.

0: https://patents.google.com/patent/US20160047904A1/en?q=time&...

1: https://linx.wot.lv/selif/s5ylbs51.jpg

2: http://www.ti.com/product/TDC7200

[Animats]

Short range low cost time of flight devices are usually modulated-beam things. You modulate the outgoing light with an RF carrier around 20MHz or so, and then detect that carrier on the receive side. Measure the phase difference between the two to get distance. There's a neat trick borrowed from FM radio to do this - down-convert both input and output signals with the same local oscillator. The resulting down-converted signals have the same phase difference but at a lower frequency, where you can count it easily.

[Groxx]

Are those actually referred to as "time of flight" devices though? Phase-difference measurements are cheap and extremely effective, but I usually see them labeled as such.