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Thread: Analog VU meter on ILI9341 TFT display (cooperation wanted)

  1. #1
    Member DIYLAB's Avatar
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    Analog VU meter on ILI9341 TFT display (cooperation wanted)

    Hi,

    I have quite a rich audio project that consists of several modules. I have been working on it for a year already. The project consists of the Teensy environment and a desktop configuration program (C#) for the individual modules.

    One module is the replication of an analog VU meter on a 3.2" TFT display with ILI9341 controller.
    The hardware used besides the display is Teensy 4.0 and Audio Adaptor Rev. D .
    The module works well so far. It runs with constant 120 FPS and vSync and draws the needles with edge smoothing. The ballistics are defined by constants.

    There was in the original thread in a HiFI forum a visitor with great knowledge, but in his only posting only gave valuable tips, but I can not implement alone. That exceeds my knowledge enormously.

    Therefore the question here - do you have interest to work on it?
    In this case I would decouple the module and provide it for the forum, i.e. as source.

    Since this module is a VU meter and VU is specified exactly, there is a need at this point: IIR filter for integration time, a second IIR filter the return time.
    I have no idea about filters :/

    Here are two parts from the text that seem particularly important to me:

    "I can comment on some things. In vain we used ready-made functions RMS, PEAK. You can, of course, pick up the ballistics by eye using conventional numbers, but it is better to use standard time constants, as prescribed by IEC 60268-10. It is necessary to work directly with the samples of the audio signal. They are first rectified (the modulus is calculated), then the IIR filter of the first order forms the integration time, the second IIR forms the return time. Also, the response time and the holding time are usually used, which is also easy to implement. Ballistics will be given in ms according to IEC."

    "If you want to make a VU for compatibility with old indicators, then you must observe its characteristics. Standard VU is implemented with a second order filter with a cutoff frequency of 2.1 Hz and a Q factor of 0.62."

    Who wants to participate?

  2. #2
    Junior Member
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    what a nice project, following closely!

    sry but i cant help much.

  3. #3
    Member DIYLAB's Avatar
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    Thank you for your interest!
    Someday I may understand how to program such a filter - with age comes wisdom ;o)
    Meanwhile the project is also on GitHub.

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