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Discussion in 'Electronic Design' started by merco, Feb 19, 2007.

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  1. merco

    merco Guest

    is it possibile to use 4046 as a tone decoder ?
    I'd like to use the hook indicator as detector for a 440Hz sine wave
  2. Tim Wescott

    Tim Wescott Guest

    A PLL will decode pure tones. To use the 4046 you'll have to square up
    the audio into a logic signal. Once you've done that set up the 4046 to
    lock on the tone of interest, use the VCO drive as a frequency reading
    and (if it's pure enough) the lock pulses to tell you if the tone is
    really there.

    Having said that, there are probably _much_ better ways of doing this,
    particularly since you could probably do some DSP Lite in some little


    Tim Wescott
    Wescott Design Services

    Posting from Google? See

    "Applied Control Theory for Embedded Systems" came out in April.
    See details at
  3. René

    René Guest

    Amazed to see it still exists...decades ago I built telex and morse
    decoders with it, using the same oscillator in the 567 to generate
    telex / morse signals.

    (dreams of using the Commodore 64 to decode funny agressive
    anti-capitalist Russian propaganda telex...damn - I get old)
  4. Rick

    Rick Guest C64 is sitting on the shelf only a few feet away. Used it for the same things and
    controlling a DX440 : )
  5. Ken Smith

    Ken Smith Guest

    The XOR phase detector will work with a fair amount of noise. You need to
    prevent huge spikes from getting to the PLL chip so there is likely to be
    a resistor in the input signal path. You will also need a capacitor in
    series to allow the PLL input to self bias.

    --- 1N914
    ! 2.2nF !
    --/\/\---+--+-------+-----!!----! Sig in
    22K ! ! !
    --- ---
    1N914 ^ --- 22nF
    ! !

    You will want a counter chip so that the VCO output can be made to run at
    4 times the 440Hz input. Assuming there is enough noise, you can decode
    the "I'm locked" signal with a quad XOR gate chip.
  6. Ken Smith

    Ken Smith Guest

    No, the 4046 will do the squaring up for you. You just need a capacitor
    to let is self bias.
  7. john jardine

    john jardine Guest

    Yep!, the same dreams. Used the XR2211 demod chip. Vary, Baud, shift,
    damping, centreF. Components calculated on the Sinclair Spectrum then in
    turn programmed to do datastream to text. Then add inline audio notch
    filtering and amps. Move then onto communications receivers ... Happy days.
    Learnt a lot stuff but mainly the niceness of Z80 machine code and the need
    for fast, efficient programs.
    Won't throw the kit out as there's 6 months of my locked life in it :)
  8. merco

    merco Guest

    Oh, thanks...
    Can you help me qith the design ?
    What capacitor ? 220nF ?
  9. Ken Smith

    Ken Smith Guest

    See the ASCII art I did. Look at a 4046's data sheet. Do a bunch of
    calculations like:

    F = 1 /(2 * PI * R * C) or C = 1 /(2 * PI * R * F)

    You'll catch on.

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