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What impact should sunlight have on the returned value?

videojames
Associate III

From what I gather, sunlight causes the sensor to return a much larger value. Should this always be the case? Or is sunlight going to cause a variety of different values.

I have mixed results in testing.

1 ACCEPTED SOLUTION

Accepted Solutions
John E KVAM
ST Employee

A truly great question.

The photons the sensor emits are not marked in any way save that they are at 940nm. So there is a band pass optical filter on the Receive side to eliminate all the other photons.

But the sun emits a lot of 940nm light. (Oddly not as much 940 as one might expect. Water vaper in the atmosphere absorbs it.)

At the beginning of the range, we take a measure of the 940nm light. This is the Ambient that you can get after the range.

What we are looking for is that signal over ambient.

But if the Single Photon Avalanche Diode (SPAD) array is fully saturated by the sun, there is nothing we can do.

But generally at the closer distances, the target obscures some of the sunlight and we can get a range. Also direction is important. Sunlight passing at 90 degrees to the sensor and the target has less effect on the sensor.

All this taken together means that a sensor that can range to several meters indoors, will be limited to maybe a half meter in bright sunlight.

But the good news is that if there is a returned value, it will be right. The sunlight stops the ability of the sensor to work, but does not corrupt the answer if there is one.


In order to give better visibility on the answered topics, please click on 'Accept as Solution' on the reply which solved your issue or answered your question. It helps the next guy.

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1 REPLY 1
John E KVAM
ST Employee

A truly great question.

The photons the sensor emits are not marked in any way save that they are at 940nm. So there is a band pass optical filter on the Receive side to eliminate all the other photons.

But the sun emits a lot of 940nm light. (Oddly not as much 940 as one might expect. Water vaper in the atmosphere absorbs it.)

At the beginning of the range, we take a measure of the 940nm light. This is the Ambient that you can get after the range.

What we are looking for is that signal over ambient.

But if the Single Photon Avalanche Diode (SPAD) array is fully saturated by the sun, there is nothing we can do.

But generally at the closer distances, the target obscures some of the sunlight and we can get a range. Also direction is important. Sunlight passing at 90 degrees to the sensor and the target has less effect on the sensor.

All this taken together means that a sensor that can range to several meters indoors, will be limited to maybe a half meter in bright sunlight.

But the good news is that if there is a returned value, it will be right. The sunlight stops the ability of the sensor to work, but does not corrupt the answer if there is one.


In order to give better visibility on the answered topics, please click on 'Accept as Solution' on the reply which solved your issue or answered your question. It helps the next guy.