BMA253 Activity Detection

[samd_jldtech]

Hello,

I am working on an application with the BMA253 and am running into issues with the sensitivity of the device.

After reviewing the datasheet and comparing the modes to what we need for our applications, we have configured the device in the slow motion interrupt setting with 2g sensitivity and tried varrying bandwidth, threshold, duration, the low power modes, and sleep durations. 

Our device has two similar applications: a wrist wearable and pocket token. They both need to detect whether the user is active and in motion and has a timeout to determine if the user has ceased motion or taken the device off their person. 

Currently our settings cannot detect the smooth motion of walking even though it is so sensitive that while sitting on a desk, it registers when someone is typing on a keyboard.

Can you provide any guidance on the proper configuration of the BMA253 for our application? Are there some pre-defined and tested settings approved for a wearable & pocket motion/activity tracking?

Thanks,

Sam

[FAE_CA1]

Hi,

Thanks for your inquiry.

You can use BMA253 high-pass filter and high-g interrupt to detect if the user is in motion or stationary. Please see the attached "How to generate wakeup interrupt from BMA253.pdf" for more information.

Thanks.

[gaurav1995]

I am also working on a similar case with the BMA253 sensor, could you guide me as to how to interpret these raw values to x, y and z values of the accelerometer?

here is a snippet of the raw data from the sensor:

These are 2 entries from the sensor. How do i get back xyz axis readings from this?

[61,-52,-1,124,0,42,-1,-52,-1,124,0,44,-1,-53,-1,-128,0,48,-1,-51,-1,-125,0,41,-1,-49,-1,-117,0,47,-1,-47,-1,126,0,41,-1,-49,-1,112,0,35,-1,-50,-1,118,0,39,-1,-50,-1,114,0,36,-1,-52,-1,121,0,37,-1,-50,-1,104,0,28,-1,-51,-1,90,0,34,-1,-51,-1,98,0,31,-1,-49,-1,116,0,31,-1,-50,-1,116,0,30,-1,-50,-1,116,0,30,-1,-51,-1,99,0,30,-1,-55,-1,120,0,36,-1,-58,-1,-116,0,41,-1,-54,-1,115,0,33,35]
[61,-48,-1,90,0,27,-1,-47,-1,102,0,29,-1,-51,-1,111,0,41,-1,-51,-1,90,0,26,-1,-54,-1,99,0,33,-1,-54,-1,101,0,32,-1,-51,-1,104,0,29,-1,-49,-1,93,0,36,-1,-48,-1,110,0,30,-1,-50,-1,97,0,26,-1,-54,-1,113,0,35,-1,-52,-1,117,0,33,-1,-53,-1,110,0,34,-1,-52,-1,114,0,36,-1,-52,-1,123,0,31,-1,-52,-1,120,0,38,-1,-51,-1,90,0,39,-1,-51,-1,105,0,40,-1,-50,-1,106,0,31,-1,-52,-1,106,0,34,-31]

[FAE_CA1]

Hi,

Thanks for your inquiry.

Please use Hex values for BMA253 data registers. For example, at +/-2g full scale range, the sensitivity is 1024LSB/g. If you get the values from data registers from 0x02 to 0x07 like below,

[0x51, 0x03, 0xE1, 0xFF, 0x81, 0x40], then,

x = 0x0351 >> 4 = 0x0035 = 43LSB = 43/1024 = 0.042g = 42mg

y = 0xFFE1 >> 4 = 0xFFFE = -2LSB = -2/1024 = -0.002g = -2mg

z = 0x4081 >> 4 = 0x0408 = 1032LSB = 1032/1024 = 1.008g

So it means that BMA253 z axis is pointing to sky, while x and y axes are flat.

Thanks.

[gaurav1995]

[-48,-1,90,0,27,-1]

Ok so i here i am getting values like this rather than hexadecimal. How would i proceed here? The sample i sent earlier are not hexadecimal values.