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BCD with DDS chip

Discussion in 'Electronic Design' started by Steve Jonson, Mar 28, 2007.

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  1. Steve Jonson

    Steve Jonson Guest

    I am interested in using something like the AD9851 DDS chip to
    generate audio sinewaves but controlling it with BCD swtiches instead
    of a serial input. IOW I need it to be independent of a computer or
    micro. Can anyone advise where I can find the information to do this,
    or provide a summary of the technique?

    Regards,

    Steve Jonson
     
  2. Uwe Bonnes

    Uwe Bonnes Guest

    Add a small microcontroller to read the BCD switches, calculate toe needed
    SPI Pattern and transfer it to the DDS.
     
  3. Almost certainly the sensible answer is to use a micro, though there
    could be some situations where an FPGA might make sense. The math you
    need, including a 32-bit BCD->binary conversion is not very convenient
    for discrete logic.


    Best regards,
    Spehro Pefhany
     
  4. MooseFET

    MooseFET Guest

    How good does it have to be? It may be easier to make a DDS circuit
    that runs in BCD than to convert for the AD9851. This would be much
    more likely if you only need one or two digits and can stand some
    distortion.


    If you must convert BCD to binary and need to avoid all programable
    parts, you may be best off using programable BCD counters to control
    how many pulses go into a binary counter.
     
  5. John Barrett

    John Barrett Guest

    gonna take you far more in the way of discrete logic than it would with an
    MCU -- you can get the entire functionality needed in an 18 pin dip and a
    one-of-8 decoder (to select the BCD switch for reading)
     
  6. miken

    miken Guest

    Have a look at http://www.hanssummers.com/radio/dds/index.htm
    I'ts using binary switches, not bcd, but you could decode bcd to get
    binary and input that as per the circuit on the link.

    Regards MikeN
     
  7. Do you think that approach is feasible with a 32 bit binary output?


    Best regards,
    Spehro Pefhany
     
  8. MooseFET

    MooseFET Guest

    Yes, for very small values of feasible. 7 Minutes isn't that long of
    a time.

    I wasn't, however, thinking of numbers that long. 6 digits would be
    quite reasonable and since the oscillator this is driven from is
    likely less accurate than that, this is likely to be enough.
     
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