Local Communication by using multiple VL53L1x

[CBila.1]

Hi,

I plan to use a VL53L1x sensor pair to implement a very low-bandwith local communication as a side duty of ranging. For this purpose I need to be able to precisely control laser emission of VCSEL. Is is possible to timing VCSEL laser emission by using the official APIs published by ST ? or switching on and off VCSEL supply and ground ?

Thanks for your time.

[John E KVAM]

Unfortunately you can't do that. The microcode burned into the sensor itself has control of the VCSEL. And although we think of the laser being 'on' while ranging, it's really pulsing at about a 30% duty cycle.

In theory the sensor has everything you need, but there is no real control over the VCSEL or the SPAD photon detector.

• john

[CBila.1]

First of all, thank you for your response.

"In theory the sensor has everything you need, but there is no real control over the VCSEL or the SPAD photon detector."

I think this part from your answer is really upsetting and I do not understand why ST takes such an attitude regarding this magnificient piece of hardware such as not publishing register map of the device and not giving more control to the user. Please correct me if I am wrong.

Nevertheless, even if I have not any control over VCSEL seperately I have control over start, stop times and duration of ranging cycles right ? I think max. rate for ranging with decreased resolution is 100 hz ( thus, less than 10ms timing budget).

So by controlling duration, start and end times of ranging cycles (by using setTimingBudget(), StartRanging(), StopRanging() functions of the API) I can really perform very low bandwith comm. (~100bit/s). For example if I would like to send 101 sequence I can setTimingBudget(10ms) StartRanging() wait 10ms StopRanging() wait 10ms without ranging and StartRanging() wait 10ms StopRanging(). Actually, for my project even 8bit/s is a good value for my comm.

What do you think about it ?

And in order to observe VCSEL emission pattern can I use an ordinary photodiode (940nm) connected to a scope ?

[John E KVAM]

This is a hard one. Basically ST will build a chip for you if you tell us you will buy 25million or so. It takes a lot to get us to do anything. But I'm guessing you are not buying 'cellphone quantities'.

The Imaging group is really not that large and a few really big customer eat up all our available bandwidth.

Sorry about that. I actually had the same idea years ago, and I got nowhere.

but if you wanted really, really low bit rates I suppose you could set a timing budget for 15 ms, do the range, reset the timing budget for 20ms and do another one. do 15ms for a 0 and 20ms for a one.

But I'm thinking an LED and photodetector can do the same job much easier and I'm thinking cheaper, but perhaps larger.

• john