topic Re: Motion Detection MMA8451 in Sensors

Motion Detection MMA8451

luigi5hd — Tue, 03 Feb 2026 22:18:22 GMT

Goodmorning,

I've enabled the motion detection and now when my acceleration on the X-axis exceeds the threshold it works fine, but I want also that it continues to collect data while the device is moving at constant speed (acceleration = 0).

Does exist some embedded register to use the deceleration (breaking) as threshold for stop collecting data?

Thank you for you time.

Luigi

Re: Motion Detection MMA8451

TomasVaverka — Wed, 16 Jan 2019 08:40:37 GMT

Hi Luigi,

The configurable threshold in the FF_MT_THS register is an absolute value and you can distinguish positive vs. negative using polarity flags (XHP, YHP and ZHP) in the FF_MT_SRC register.

I hope it helps.

Best regards,

Tomas

Re: Motion Detection MMA8451

luigi5hd — Wed, 16 Jan 2019 14:32:18 GMT

Hi Tomas,

Oh sure, you're right, I'd forgotten these register's proprieties.

But I have a question, the acceleration's polarity meanings are, for instance for the X axe:

if XHE = 1 we have an acceleration

if XHP = 1 we have a braking (deceleration)

And the polarity isn't correlated to the fact that I'm going forward or backward right?

Thank you in advance.

Luigi