BMA253 Single tap

[mgchoi]

Hi, BOSCH

Use the current BMA253
I would like to use the function to wake up the MCU when an interrupt occurs using Single Tap.

Is this possible or what Resister should I use?

[mgchoi]

Hello

I have a few questions, so I'm leaving a reply.

1. Does the Single tap function react to all x, y, and z axes? (ex. Does it react to tap from above when the sensor is standing 90 degrees from the floor?)

2. Regarding 2-16g, I know that the lower the range, the more resolution it provides for slow motion, and the higher the range, the better for fast tracking, but is 16g better for detecting small vibrations?

[FAE_CA1]

Hi,

You set the bandwidth to 1KHz, but you changed the power mode from low power mode 1 to normal mode. Please follow the registers' configurations in the document of BMA253 single-tap. You should be able to see the single-tap interrupt signal.

Thanks.

[FAE_CA1]

Hi,

Yes, BMA253 single-tap interrupt reacts to all x, y, and z axes. It doesn't matter which orientation BMA253 is at (flat, or vertical or any tilted angle) and which direction the single-tap motion is applied to BMA253 (along x/y/z axes or any direction in 3D space).

If you set BMA253 full scale range to +/-16g for example, then sometimes small single-tap motion may not trigger the interrupt. So the full scale range of BMA253 is for the sensitivity of single-tap interrupt. Usually +/-2g full scale range should be sufficient.

Thanks.

[mgchoi]

Hi, FAE_CA1

Thank you for your reply.
I have a few more questions, can you answer them?

1. What is tap_th<4:0> the set range value at 62.5mg e.g. at 0x10?
     The same applies to slop_th <7:0>3.91 mg (2-grange). What is the slop_th at 0x10?

2. What is the sampling time after sleep time at bandwidth 1000Hz?

[FAE_CA1]

Hi,

1. When BMA253 is set to +/-2g full scale range, 1LSB for tap_th<4:0> in register 0x2B corresponds to 62.5mg. The pseudo code in the technical document uses 0x04 for tap_th<4:0> as an example. It means that the tap threshold is 62.5mg/LSB * 4LSB = 250mg. If you set tap_th<4:0> to 0x10 then the tap threshold will be 62.5mg/LSB * 16LSB = 1000mg = 1g.

    The same applies to slope_th<7:0> in register 0x28. When BMA253 is set to +/-2g full scale range, 1LSB for slope_th<7:0> corresponds to 3.91mg. If you set slope_th<7:0> to 0x10 then the slope threshold will be 3.91mg/LSB * 16LSB = 62.56mg. Slope means the current acceleration value minus previous acceleration value, i.e. Delta ax_t = ax_t - ax_t-1 for x axis. If Delta ax_t is beyond the slope_th threshold for the amount of duration, then slope interrupt or any-motion interrupt will be generated. BMA253 single-tap and double-tap interrupts use Delta ax, ay, az as input.

2. When BMA253 bandwidth is set to 1000Hz, the sampling rate is 2000Hz which means the sample time is 0.5ms. Please see the attached Excel file for more information.

Thanks.