Using lis3dx to detect the acceleration threshold in a car accident

Forum|Forum|7 years ago
March 23, 2018
2 replies
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Posted on March 23, 2018 at 07:53

The purpose is to detect the car accident while ignore the normal acceleration variance during car driving.

I know there is a high pass filter in the lis3dx sensor, and the cut-off frequency can be changed by setting the following register (with actual cut-off frequency related to ODR setting) but don't know how to choose the best value. I guess there is experience value for the ODR and HPCF settings in car application. Anyone have relevant experience and would like to share it with me?

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A

Anonymous

Posted on March 23, 2018 at 08:39

Hello,

I don't think anyone will write any typical values for a car accident here. There are so many variants! This is why car manufacturers and safety systems manufacturers do millions of hours of testing.

Are you sure you need the high pass filter? If you eliminate the gravity, you loose the sense of the gravity direction and that is not good. What if the car is rolled over a roof? Is that an accident?

Also, if a fender bender an accident for you? Most of the fenders are made from plastic and they soften the first part of the impact. That is why there are usually other sensors embedded, because time is critical in order to fire the airbags and seatbelts, etc.

However, if you are building just some hobby project, it might be sufficient to just experimentally set value and time threshold.

Here is some reading:

https://www.wired.com/2011/04/crashing-into-wall/

David

K

Kefei YaoAuthor

Visitor II

Posted on March 23, 2018 at 12:04

Thank you very much for your input and reading material. They are extremely helpful.

The real-time quality of the accident detection in my application is not that critical so no question about that. It's a product that help mark the video taken by the camera in case of car accident. Yes, a car rolling over a roof is definitely a car accident but it still can be detected by the lis3dx sensor even if the high pass filter is applied, can't it?

The reason I'm asking about the high pass filter setting is because the high pass filter can help attenuate the acceleration signals generated in normal car driving which is rather gentle in most cases. Also high pass filter can help remove the dc components.

I also find with the same threshold and duration setting, the lower HPCF setting can cause the interrupt trigger more easily in case of normal car driving. I deduce that the lower HPCF attenuate the signal generated in normal car driving less and cause the interrupt trigger easily.