Aalborg University has developed a“Low Frequency Sound Meter” - what can it do?

1) Display current (125 ms exp.) sound pressure level in the range of 12 to 35 dB(A,LF) on 24 LEDs.

2) Record the sound and save it, max 2 mins per file.

3) Transfer the newest files (i.e. recordings) via the Internet to an AAU server.

4) Provide a simple UI “Everybody” can use the device.⇒

5) Permit the user to find the spot where there is more (annoying) sound. (sounds trivial...long story...)

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The appearance of the sound meter

Original prototype is currently in Holbæk!

But, on the table: 1) Development board (for a board :-) plus2) Colleague Sofus’ power on/off...board.

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Imagine household without a Low Frequency Sound Meter…

The project’s (initiated on May, 2013) personnel

“Drawer-project” where we as often as possible would open that drawer, find old stuff and possibly add more...

⚫ DH, HM: Adm. and orig. idea. Photos, manual/guidance etc.

⚫ CP, CV: Development of physical calibrator, chosing microphone(s).

⚫ CV, FC: Hardware-design incl. print, anti-aliasering filter (for downsampling), Matlab-template for analysis.

⚫ SBN: Power On/Off-circuit (hardware).

⚫ PED: Network. Dedicated AAU-server, adm. + setup.

⚫ SKO: DSP/filter-design, software.

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No exact master plan

⚫ So...ideas were made up ad-hoc. E.g. the fact that all measurements should be recorded (and saved).

⚫ New ideas just called for new development which in turn called for new ideas etc.

⚫ Ending point: Lack of new ideas (never really happened).

Special features implemented

⚫ If a USB stick is inserted, all files would be copied there automatically; that was practical for debugging in general. Partly dropped in later versions.

⚫ If a camera USB cable is inserted the device would recognize that and copy all files on the camera to the SD-card on the system. Later to be sent via the Internet to the AAU server.

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Hardware overview 1:2

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Hardware overview 2:2

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Hardware design example

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Software overview 1:2Organization

Main thread

UI thread

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Software overview 2:2Signal path

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Software requirements and considerations

⚫ Superior to existing...e.g. Gumsticks due to FP capabilites.

⚫ Raspian OS installed. Note: Pi3 has Wi-Fi but of no usage in this case. Everything must be cabled.

⚫ All C. No C++, Python whatever, yet, a few system() calls.

⚫ WiringPi. To access GPIOs more easily.

⚫ Advanced Linux Sound Architecture (ALSA).

Software problems

⚫ 44.1 vs. 48 kHz, zeros found in the sampled buffer.

⚫ A PC-emulator would have been nice + boot time smaller.

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Flightcase to borrow

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The end

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