LIS3DH - Motion and crash detection

[Arek Arkowski]

Posted on February 26, 2018 at 12:02

Hello all

My goal is to use two INT pins to generate two interrupts in a device which will be used in a car. INT2 will be pulled when a crash of the car is detected and INT1 when the car moves.

Here is my init setting:

CTRL_REG1 = 0x27 //10Hz, normal power mode, ZXY enable

CTRL_REG2 = 0x01 // HP filter for INT1

CTRL_REG3 = 0x40 //IA1 enable

CTRL_REG4 = 0x90 //4g | BDU

CTRL_REG5 = 0x0A //latch on INT1 and INT2

CTRL_REG6 = 0x22 //active low & INT2 enable

INT2_THS     = 0x6D //~3500mg

INT2_DURATION = 0x00 // 0.1*0s 

INT2_CFG     = 0x2A  //OR, X,Y,Z higher than threshold

INT1_THS     = 0x02 //

INT1_DURATION = 0x03 //

INT1_CFG    = 0x2A //

Generally, the motion detection part works fine (thanks to Miroslav). I am concerned about the crash detection part.The threshold is quite high (I don't want it to interrupt on every bump on the road) but it still sometimes interrupts when no hight acceleration is applied. It is very rare but still occurs. 

If you have any inputs to this I'll appreciate.

[Miroslav BATEK]

Posted on February 26, 2018 at 14:33

I think the threshold depends on the sensor location and stiffness of the mounting.

I'm not expert on automotive but I think the threshold 3.5g is not so high, this peak value can be generated during standard operation.

Please be aware there are dedicated

http://www.st.com/content/st_com/en/products/mems-and-sensors/automotive-sensors.html?querycriteria=productId=SC1946

 and accelerometer for airbacks which have full scale 100g or 200g.

[Arek Arkowski]

Posted on February 26, 2018 at 18:19

You're right. I'll try with 8g.

[Arek Arkowski]

Posted on April 17, 2018 at 00:21

I would like to go back to this question since I still struggle with it.

I modified the configuration so it looks like this:

CTRL_REG1 = 0x27 //10Hz, normal power mode, ZXY enable

CTRL_REG2 = 0x01 // HP filter for INT1

CTRL_REG3 = 0x40 //IA1 enable

CTRL_REG4 = 0xB0 //16g | BDU

CTRL_REG5 = 0x0A //latch on INT1 and INT2

CTRL_REG6 = 0x22 //active low & INT2 enable

INT2_THS     = 0x7F //max

INT2_DURATION = 0x00 // 0.1*0s 

INT2_CFG     = 0x2A  //OR, X,Y,Z higher than threshold

INT1_THS     = 0x01 //186mg * 1?????

INT1_DURATION = 0x03 //0.1s * 3

INT1_CFG    = 0x2A //

Now with full scale 16g when the threshold is set to 186mg it constantly interrupts, even when the device remains in place!  Changing it to 372mg helps but it is too much for me. Before when full scale was 8g and the threshold value was 128mg I didn't have such problems. What might be a reason of such behavior?

[Miroslav BATEK]

Posted on April 17, 2018 at 08:45

The reason of this behavior is most probably offset of the sensor.