Adding SPL option to Nordic Thingy:52

[Dimitar]

How do you think - is there resources enough to add SPL (sound pressure level) measurement functionality into Nordic Thingy:52? Is microphone appropriate or may be external one is needed?

From this DIY meter davidegironi.blogspot.se/.../a-simple-sound-pressure-level-meter-spl.html

steps are following

1. collects N samples 2.do FFT for the N samples collected, the signal is now transformed in the frequency domain 3.apply A or C weighting (in freq domain) 4.get magnitude of the signal
2. get RMS value of the signal
3. apply a time-weight filter to RMS value (fast or slow) 7.compute the SPL using the RMS value 8.output data

and also add calibration possibility (with sound calibrator 94db@1kHz, 105db@1kHz).

Since sound measurement is quite intensive in terms of sampling and logging, best way to save battery probably be measure each second and log only values above certain levels. Or make active measurements only above certain sound level.

Thanks for all that reading and answering.

[bjorn-spockeli]

Hi Dimitar,

if Davide Gironi is able to implement this on an Atmega328, then you should have no issues implementing this on the Cortex-M4F of the nRF52832 used by the Nordic Thingy:52.

We have an FFT example in the SDK, see this Infocenter page, that uses the FPU peripheral with the CMSIS DSP library. The example generates sine data (with noise and without) for calculations and processes sine data with FFT every 1 second. You can use this example as a template.

As for the microphone, we're using the ST MP34DB02, which is a stereo MEMS microphone with pretty decent characteristics.

Best regards Bjørn

[Dimitar]

Sounds great, let's see :) Thanks Björn!

[tushar19]

Hi..Did you got the desired results???