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  1. #1

    Question digital filter

    Hi
    I want to calculate this expression:

    y_n=(b0*x_n)+(b1*x_n_1)+(b2*x_n_2)+(b3*x_n_3)

    -(a1*y_n_1)-(a2*y_n_2)-(a3*y_n_3)
    That:

    x_n;x_n_1;x_n_2;x_n_3;y_n;y_n_1;y_n_2;y_n_3;a1;a2; a3;b0;b1;b2;b3
    are variables and their type is Word.

    Infact I want to use this equation for implementing a digital filter
    maximum order of filter is 3.
    I must input a1;a2;a3;b0;b1;b2 and b3 from keyboard.These valuse can be
    negative or positive.I use PICBasic Pro compiler and PIC16F877 MCU.I am a
    beginner therefore I get in to trouble;My problems are:

    1-I know that pbp uses unsigned integers but I want to input
    signed values from keyboard please help me how I can do that.

    2-Suppose that the result of (b0*x_n)+(b1*x_n_1)+(b2*x_n_2)+(b3*x_n_3)
    has overflow because type of my variables is word how I can prevent
    this event.

    3-Suppose that the coefficients are float for example a1=0.2
    a2=6;a3=-0.6 In this case how I can calculate above equasion.

    Any suggestion would be helpful for me specially number 1 and 3 questions.
    Thank you very much.

  2. #2
    magix's Avatar
    magix Guest

    Default

    I suggest you to make Moving Average Filter. It is expecially suited for microcontroller application.
    It is very fast and very effective.

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