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converting line level audio to resistance?

Discussion in 'Electronic Design' started by Mad Scientist Jr, Sep 19, 2005.

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  1. I need to take a line level audio signal and convert it to resistance
    in the range between 0 Ohm and 1 MOhm. Is this difficult to do for a
    beginner in electronics?
  2. John Fields

    John Fields Guest

    Well, zero ohms is the tough part, but even tougher than that is
    having to cut and paste and repost or retype and repost earlier
    replies because a querying poster (you) didn't crosspost to all the
    groups where the question was presented. Your newsreader has a box
    where you enter where you want your post to be sent, and if you fill
    in all the groups where you want it to go the first time you send
    it, it'll be sent to all of them automatically and then anyone
    reading your post in any of those groups and replying to it will
    send replies to all of the other groups as well. That's called
    "crossposting" and makes life a little easier for us all, so why not
    try it?
  3. I read in that Mad Scientist Jr
    Not difficult, just impossible. Now say what you are really trying to
    do, and we may be able to help.
  4. Pooh Bear

    Pooh Bear Guest

    With a name like Mad Scientist I'm sure it's right up your street
    ! ;-)

  5. Pooh Bear

    Pooh Bear Guest

    V = I*R

    therefore R = V / I

    So all you have to do is divide the voltage by the current.

  6. Fred Bartoli

    Fred Bartoli Guest

    Just convert all the possible line levels to 1K.

    Plain easy, even for you.
  7. Ol' Duffer

    Ol' Duffer Guest

    It's not entirely clear to me why a responder would want or need
    to cut and paste, but with modern software it's arguably easier
    than having to dig for a post that mysteriously disappeared because
    you marked it "read" in some other newsgroup. Which is why some
    folks prefer multiposting to crossposting.

  8. Well, so far you seem to be getting responses that, while perhaps relevant,
    might not be helping you solve your problem.

    That might be partly because doing what you suggest is a bit unusual, and it
    might be that you are approaching whatever broader problem you are trying to
    solve in the wrong way. So if you tell us what you're trying to do, that
    would help.

    But to answer one thing I think you might possibly be asking: if you mean
    that you want to create a device that has an audio line level input and an
    output that behaves like a resistor whose value varies predictably with the
    input voltage, yes it can be done but it is challenging. The hardest parts
    are getting it to be linear (or logarithmic or whatever you're aiming at),
    and getting it to be fast enough to deal with audio frequencies. (And as
    others pointed out, the 0 ohm part is impossible; you might be able to get
    10 ohms, or maybe even 1 ohm, but 0 is physically impossible.) Think in
    terms of using the input voltage to control the drain-source resistance of
    an FET.

    There are a lot more aspects of this you'll need to specify in detail in
    order to get a more useful answer.
  9. Fred Bartoli

    Fred Bartoli Guest

    IOW, you're begging for some information and you think others have to suffer
    the inconvenience you create just because you don't want to bother being
    careful enough?

    How selfish you're.
  10. René

    René Guest

    A very imperfect realisation of the above is using an audio amp to
    drive a lamp rather than a speaker, and have it's light shine on an
    old fashioned LDR. (This would sort of transform the audio average
    *volume* into sort of resistance)
  11. John Fields

    John Fields Guest

    You seem to have missed the point, which is that If I respond to a
    post in, say, seb and then, later, find that identical post in sed
    (but not crossposted) I will either have to not respond, go back to
    seb, locate and copy my earlier response, then go to sed, find the
    OP's post, paste my response into it and, finally, send it, or
    retype a separate response.

    As far as software goes, I think it's relatively easy to set up a
    newsreader so it marks posts read but doesn't kill them. At least I
    don't have that problem, and I'm using Agent.
  12. That's an interesting idea - how would you get the circuit to max out
    at 1 MOhm and at a minimum, go to as close to 0 ohms as possible?
  13. Deefoo

    Deefoo Guest

    Now that's a cool idea. Let your stereo do the playing for you while you get
    on with your life...

    The way your pots are connected suggests that your game is already voltage
    driven, so you would only have to amplify your audio to cover the 0-5V
    range. For starters try connecting your audio output directly to the paddle
    pin (and gnd to gnd) and see what happens.

  14. I'll just end this subtopic and say I was a dumbass and multiposted by
    mistake - I posted and then had a 2nd thought "maybe it would be better
    in .design instead of .misc" and posted there too. Sorry for the
  15. Very good, very good indeed ;)

    I was about to suggest a fixed 470K resistor and forget about the
    audio signal.

  16. I'm not clear whether you want the resistance to be related to the envelope
    (average volume) of the signal, or to the instantaneous voltage.

    Are you trying to make something like an oscilloscope, to display something
    like a Lissajous pattern (ever-changing squiggly thing that shows phase and
    frequency relationship between two channels)? Or are you trying to make
    something that just moves the paddles depending on how loud the sound is?

    If the former, you're probably out of luck; I don't think the Atari itself
    will respond to paddle movement at 20kHz.

    If the latter, then Rene's light bulb idea is not a bad one. One problem is
    that light-dependent resistors (LDRs) with 1MEG dark resistance are usually
    pretty slow, taking as much as several seconds of darkness to get all the
    way to 1MEG. The resistance will go low in a hurry, but it takes a long
    time to recover to high - it's sort of like your eyes when they dark-adapt.

    Either way, you probably only need a current or a voltage, not a resistance.
    That's considerably easier. And I wouldn't worry about getting the
    (effective) resistance any lower than 1k ohms, since the pots in the
    joystick are almost certainly linear (as opposed to log-taper): the
    difference between 1k and 0 is 0.1% which is less than the pots themselves
    can distinguish.

    Give Rene's idea a try, as a start. If it doesn't work you can evolve it.
  17. John Fields

    John Fields Guest

  18. Maybe it's this damn google groups interface, you click Reply and
    assume it is quoting the original article and then it doesn't
    let us know what you're responding to then we won't have to digging
    for it.
  19. That sounds easy, I will need to multimeter it.

    2 dangers:

    1) blowing up the stereo if the output resistance is not 8 ohms (or
    whatever the output expects for headphones) - that's why I originally
    said Line Level, this would be a single standard as opposed to
    different stereos which need different resistance speakers.

    2) blowing up the video game - it sends 5v out and measures how much of
    that comes back. I assume the signal from the stereo sends voltage as
    well. So what happens when you have the 5V from the game, plus the
    volts from the stereo? What if the game can only handle at most the 5v
    it is sending out? Therefore, I would rather make a circuit that 1)
    controls resistance 2) provides some attenuation so the stereo doesn't
    blow up

    on with your life...

    The way your pots are connected suggests that your game is already
    driven, so you would only have to amplify your audio to cover the 0-5V
    range. For starters try connecting your audio output directly to the
    pin (and gnd to gnd) and see what happens.

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