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Thread: Starting Audio FFT from interrupt

  1. #1
    Junior Member
    Join Date
    Dec 2017
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    Riga, Latvia
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    Starting Audio FFT from interrupt

    Hello!
    I'm working on project regarding industrial DC power and "returning" DC power supply (not watts but kilowatts) in industry.
    In order to evaluate different power converters FFT is very handy tool and Teensy FFT1024 are good in a lot of cases.
    But - looking through Audio library I cannot find a way how to start FFT from interrupt. I want to start several FFT processes un several Teensy 3.6 at the same moment.
    Interrupt is well known tool to start something at the same moment.
    Till now I have implemented 15 pcs of Teensy 3.1 based power measurement / logging devices for fast and synchronised bi-directional DC (600V) and 3-phase mains power measurements up to 400 KW every 20ms.
    I can conclude that Teensy 3 work perfectly in to hard (from EMC point of view) industrial environment (noise from 230 KW aluminium spot welding, for example), installed directly in to electric power cabinets.
    Now is time for synchronous FFT and due to my very successful experience before I'm interested to perform synchronous FFT (via interrupt) on Teensy 3.6 base. May be one have experience how to do that?

    Other point is possibility to slightly tune chip clock. Can it be possible to use small trim capacitor and quartz in serial connection?

    Thanks in advance!

  2. #2
    Senior Member
    Join Date
    Jul 2014
    Posts
    1,878
    You have multiple Teensies running asynchronously, so you would not have synchronous results, even if the FFT's are all started at the same time. This is due to 3 ms block size.

    Would it be acceptable to let the Teensy acquire data and perform the FFT continuously, and you read out the spectral values on interrupt?
    (a couple of ms difference must be considered)

    Alternatively, what about starting acquisition on trigger on all teensies until 1kFFT is done? This would also synchronize ADC, but you have a response time of 8*3 ms (or little more to allow for initial transient).

    Re: Tuning system clock. This can be done via SW (FrankB played even 96 MHz FM music some time ago). So, a couple of kHz at 100 Mhz should be possible

  3. #3
    Junior Member
    Join Date
    Dec 2017
    Location
    Riga, Latvia
    Posts
    8
    Thanks, WMXZ! I'll think about it.

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