VL53L1X SignalRateRtnMegaCps and AmbientRateRtnMegaCps Acquisition Principles

[jiaxuan616]

I am currently working with the P-NUCLEO53L1A1 evaluation kit for the VL53L1X sensor and have encountered some technical questions. I would appreciate your insights.

From the official documentation, I understand that SignalRateRtnMegaCps represents the target reflectivity, while AmbientRateRtnMegaCps indicates ambient light intensity. I plan to use these parameters for imaging purposes but have been unable to find detailed information on their acquisition principles in the API documentation or related materials.

I have reviewed the datasheet, application notes, and online resources, but most available content only covers basic introductions and simple use cases rather than in-depth explanations of the internal signal processing methods.

My current understanding is that the sensor emits laser pulses and measures the returned signal. SignalRateRtnMegaCps likely corresponds to the strength of the reflected signal, while AmbientRateRtnMegaCps may represent ambient light detection. However, I lack clarity on how the sensor distinguishes and processes these signals internally.

Could you please share any technical details or documentation regarding the acquisition principles of these two parameters? Any advice or experience related to implementing imaging functionality would also be greatly appreciated.

[John_Kvam · Accepted solution]

This is a bit of a tricky one, but perhaps I can help.

So the signal rate and the ambient rate are just side effects of what is going on, and the units are not particularly useful for the user. 

But let's try this ... The sensor returns a signal rate, ambient rate, and number of SPADS.

Take the signal rate and convert it to Signal per SPAD. This will give you a good indication of what you are looking at.

Say a light gray target returns 20M samples but uses 100 SPADs to get that 20M. This means the target at that distance gives a signal strength of 20M/100 or 20,000.

But now take a white sheet of paper. You will get the same 20M samples but maybe only use 50 SPADs, giving you a signal rate of 40,000. 

So it can be said the white is twice as reflective as your light gray. AT THAT DISTANCE.

The light dissipates as a square of the distance, so the distance is important.

There is a limit to this concept though. The signal rate is only relative to this sensor. If you try to convert it to some scientific measure of light returning, you are going to have to take a lot of measurements and come up with a formula for yourself.

Try using the signal per SPAD and the Ambient per SPAD and see how you get on.

- john