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estimating stereo cable resistance

Discussion in 'Electronic Basics' started by Jonathan Epstein, Oct 29, 2004.

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  1. I have a Treo 600, which includes MP3 player capability. I would like
    to plug it into the auxiliary jack on my car stereo via a patch
    cable, but there's a technical problem where the Treo mis-detects my 6
    foot cable (I would prefer a shorter cable and used to have one about
    8 inches long) as a microphone and won't emit sound over that cable.
    It turns out that the Treo will intentionally avoid emitting sound
    over the cable if it detects a resistance load in the 500-3000 ohm

    I went to measure the resistance of the 6' cable last night, but
    couldn't find my multimeter.

    So my questions are:
    (1) do you have any idea what the resistance of a 6' stereo cable is
    likely to be?
    (2) do you have any idea what the resistance of a 8" stereo cable is
    likely to be? (I might try to find & buy another)
    (3) what added resistance load is my car stereo likely to add when the
    other end of the cable is inserted into the stereo? Disclaimer: I
    don't have a detailed understanding of how all this might interact
    with car electrical system, chassis, etc.

    Ideally I would like to make this work using a short cable and make
    the load under 500 ohms, but in an extreme case I could consider using
    a very long cable and/or a resistor to force the load over 3000 ohms.
    I don't know what the latter would do to my sound quality.

    Details from two message board postings appear below. The first
    message describes my initial statement of the problem, and the second
    describes the information that I got from the manufacturer.

    Many thanks,



    I have a related question. Both my cars' stereos have a front panel
    auxiliary input jack (I bought them this way intentionally), and I
    have used them in the past with my Olympus DM-1 MP3 player and a 3.5mm
    male<->male stereo similar to this:

    Unfortunately I misplaced that cable, and went to Radio Shack last
    night and bought a replacement. Like the picture above, the ends of
    this cable visually match the tip of my mini-stereo headphones which I
    have used successfully with my Treo 600 and the Treo's elbow-shaped
    stereo adapter (palmOne Treo 600 Stereo Headphone Adapter).

    Now, for the mystery: I started up ptunes playing some music, and as
    one would expect there is no sound coming out of the Treo's speaker.
    Then I inserted the elbow-adapter, and again no sound comes out. Then
    I inserted the patch cable into the elbow-adapter, and to my great
    surprise sound came out of the Treo's speaker. I was unable to get
    sound to come out of the car stereo!

    While this is a nice trick to get ptunes to play over the Treo's
    speaker, this is not what I wanted!

    I need to go back and double-check that this new cable works with my
    Olympus DM-1 and the car stereo, but I suspect that it will.

    Has anyone encountered this situation and a solution for it? An
    explanation of this phenomenon would also be helpful.

    To clarify, I misplaced the working cable before receiving my 600 a
    few weeks ago, so I have never tested the Treo in combination with the
    working cable. But then again, I think that the new cable is
    electrically identical to the old one.
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    [] followup to car stereo using patch cable

    I would've just linked to this, but couldn't figure out how. I got
    this information by starting an email support request on the Palm

    It looks like I need to measure my cable's resistance and see whether
    it's in the 500-3000 ohm range.

    Thanks in advance for any other low-cost suggestions.


    Solution ID: 29888

    Where sounds will route with Treo 600 when using headsets and
    connecting to amplifiers

    The Treo smartphone can play MP3 music through an accessory stereo
    headset (how to play MP3 music on Treo). Please keep in mind that
    while MP3 music sounds great on a Treo smartphone, we consciously
    designed the Treo to work as a phone first, and a media player second.
    Therefore, we optimized the sound routing for telephone functions.

    When using a mono telephone headset (such as the one included in the
    box with your Treo smartphone), ringtones, alerts and media sounds
    such as MP3 music will be sent to the rear speaker on your handset.
    The sound from the phone conversation is sent to the headset earpiece.
    It is not possible to route ringtones, alerts and media sounds to the
    headset only.

    When using a stereo headset (such as the optional stereo headset
    accessory for Treo smartphones), the ringtones and alerts are mixed
    with whatever media sound is playing, and those ringtones and alerts
    play through the stereo headset. If you make a call, the phone
    conversation is routed through the built-in handset microphone and
    receiver speaker. Stereo headsets do not carry the audio from the
    phone call.

    What if the sound still comes from the rear speaker when I plug in a
    headset or cable?
    Some audio devices connected to Treo 600 may be misinterpreted by the
    automatic detection mechanism as a mono telephony headset.

    This affects how the Treo handles calls while a device is plugged into
    the socket. Some active circuits in speakers or headphones present in
    the same way as a microphone (if their impedance is from 3,000 Ohms to
    500 Ohms). In order to avoid possibly blowing a microphone, any
    ringtones, alerts or media player sound will still route to the
    built-in rear speaker on the Treo 600.

    If you use noise canceling headphones, turn off the noise cancellation
    or turn it to a lower setting to remedy the issue.

    If you are using a line-out cable to another piece of equipment,
    please be aware that we do not directly support this activity and
    cannot provide technical support to make this possible. With that in
    mind, you might be interested to know that most equipment will happily
    work with Treo 600 output. If it fails, you may need to use an
    intermediate piece of audio routing equipment that is "seen" correctly
    by Treo 600. There is no software switch to make this possible.

    For example, if you use an MP3 transmitter in your car such as the
    iRock, the Treo may not send the audio correctly thru the iRock. Other
    transmitters may appear correctly to the Treo 600.

    Trial and error is the best method of achieving success as each active
    circuit device presents a different impedance to the Treo 600.
  2. John Larkin

    John Larkin Guest

    Fraction of an ohm.
    Fraction of an ohm.

    Dunno. Measure it.
    Try a series resistor, or maybe a series capacitor would fool the
    sense circuit. Try 10K or maybe 0.1 microfarads.

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