tachometer

Discussion in 'VHDL' started by Martin Kokelmann, Jan 18, 2005.

  1. Hello,

    I want to create a tachometer in VHDL. What possibilities of programming
    are given?

    I want only ideas , no code.

    Thanks

    Martin
     
    Martin Kokelmann, Jan 18, 2005
    #1
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  2. Martin Kokelmann

    Guest

    Martin Kokelmann wrote:
    > Hello,
    >
    > I want to create a tachometer in VHDL. What possibilities of

    programming
    > are given?
    >
    > I want only ideas , no code.
    >
    > Thanks
    >
    > Martin


    Martin,

    This is a "pulses per unit time" problem. You will be getting N pulses
    per revolution from a sensor. Your problem (simplified) is to count
    these pulses for a measured time period. You can then transfer this
    count to a register that feeds a display and begin the count again. So
    you will need a clock signal to determine the time that the counter is
    enabled. A simple state machine can determine the enable time and then
    load the display register, reset the counter to 0 and restart the
    measurement cycle--you don't really need to use a state machine for
    this purpose; this is my personal preference, but you will probably end
    up with the same logic with or without the state machine and I think a
    state machine makes for easier understanding of the logic. Since the
    pulse input is not synchronous with the clock, you should use a 2-D
    flip flop synchronizer on the pulse input (this of course assumes that
    the sensor pulses are compatible with the logic family you are using).
    Another issue is converting the displayed count to RPM. The conversion
    factor depends on the number of pulses per revolution and the enable
    time of the counter.

    Best regards,

    Charles
     
    , Jan 18, 2005
    #2
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