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unable to read intermediate frequency (fmax)  values from FFT applied on vibration data recovered from LSM6DSL based vehicle  RPM Techno-meter

Question asked by VK Verma on Jun 28, 2018
Latest reply on Jul 3, 2018 by VK Verma

Hi to All !


We are working on LSM6DSL based vehicle  RPM Techno-meter with STM32L431KCU6 micro controller running at the speed of 80 Mhz. Our target is to read RPM by applying FFT F(max) on the single axis vibration data collected from LSM6DSL accelerometer from the range of F = 20 Hz to 200 Hz.

The picture of the double layer PCB board is attached herewith for your reference.

The Setting for FFT are 

  • Settings: ODR = 6000 Hz, FFT Samples = 256, Magnitude = 200mg, Full scale = +-2g
  • FFT F(max) values received are 25Hz, 50Hz, 76Hz, 101Hz, 127Hz and not like 25,26,27,28 in continuous but getting with approximate resolution of 25Hz between two consecutive values 
  • whereas we are getting Fmax values in continuous range from one of the commercially available RPM techno-meter based on MEMS accelerometer and due to this we are unable to hold the accelerator of the vehicle at the desired RPM of the vehicle for vehicle testing purposes.

Please suggest the best FFT parameter settings for the Fmax range of 20Hz to 200 Hz if we are making some mistake or suggest where we are wrong.vibration mems accelerometer


I hope we have selected right ST MEMS part for such application or suggest new another one.



Thanks in advance!


Thanks and Best Regards,

VK Verma