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MMA8452Q - False Trigger Issue With Single/Double-Tap Detection

Question asked by Joseph Ip on Nov 17, 2013
Latest reply on Dec 18, 2013 by Joseph Ip

Hello,

 

I am able to setup the chip for tap or tap-tap detection, but I found there was serious false trigger issue (simply by shaking the unit will cause the chip to generate tap or tap-tap event).

Here is the register configuration I am using:

  • ODR=200Hz (chip work in low power mode)
  • LNOISE=1 reduced noise mode enabled (0x2A)
  • PULSE_HPF_BYP=0; PULSE_LPF_EN=0 (0x0F)
  • HPF cutoff freq.=2Hz (0x0F)
  • DPA=1, ELE=1 & pulses detection for Z axis only (0x21)
  • PULSE_THSZ=1.5g (0X25)
  • PULSE_TMLT=25ms (0X26)
  • PULSE_LTCY=125ms (0X27)
  • PULSE WIND=150ms (0X28)

 

In addition, I observed that:

When LNOISE=1, it is very easy for the false trigger to happen even when PULSE_THSZ is set to 6.36g (the spec. mentioned the dynamic range will be reduced to 4g).

When LNOISE=0, it is very easy for the false trigger to happen even when PULSE_THSZ is set to 7.938g.

 

It seems to me that the PULSE_THSZ factor in the pulse detection algorithm is not working correctly.

 

I appreciate if someone could help to solve the problem or give any suggestion.

 

Thank You!

Joseph

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