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Thread: Nokia headset magic

  1. #1
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    Nokia headset magic

    As some of you may know, modern Nokia phone headsets have 4-conductor plugs, while standard headsets have 3. You may have also found out that plugging a standard headset into a modern Nokia phone does not work.

    After some playing around with my Nokia 1100, I discovered a few cool tricks.

    But first... the information to follow is just from my own experimentation, and may not be entirely accurate. Use at your own risk. I'm not responsible if you do something stupid.

    If you want to connect your own audio devices to a Nokia phone, here's the signal descriptions of the terminals in the phone's headset jack:

    TIP = earphone (+)
    RING1 = microphone (+)
    RING2 = earphone (-)
    SLEEVE = microphone (-)

    You don't have to purchase a rare, hard-to-find 4-conductor 2.5mm plug. A standard 3-conductor one will work for pretty much all your audio connection needs. It's sleeve will just bridge the earphone and microphone negative signals together, which is exactly how standard headsets are wired.

    The only reason a standard headset will not work is that standard headsets use the following wiring:

    TIP = microphone (+)
    RING = earphone (+)
    SLEEVE = common microphone and earphone (-)

    If you just swap the TIP and RING (either by rewiring your headset, or making an adapter), it will work. Apparently such adapters are also commercially available.


    Some more fun:

    The Nokia phone detects when a headset it plugged in by measuring the impedance across the earphone. This is also how the phone detects the difference between a headset and a car hands-free adapter; The genuine Nokia accessories each have a different impedance. I don't know at this time what they are, but check back in a few days and I'll have the DC resistance of each crossover point figured out, and the DC resistance of a genuine Nokia "earbud" style headset. This could be of interest if you desire the particular operating characteristics of a specific mode (ie. headset, car adapter, etc.)
    I know on the Nokia 1100, you can set it to lock the backlight on at all times when a car adapter is used, but this option is not available when a headset is used. So if you desire continuous backlighting, you may want to make an interface which fools the phone into thinking it's connected to a car kit.


    Another cool trick:

    Placing the phone into TTY/TDD mode swaps the TIP and RING1 signals, so that they do match a standard headset. So can you simply set this mode to plug in your existing standard headset? Well, only if you have super-sensitive ears and are prepared to shout into the microphone! In TTY/TDD mode, the signal levels and drive impedance change to something optimized for a proper TTY/TDD, rather than the tiny earphone and electret microphone capsule of a headset. I can't remember the name of the standard, but if you search for it, you can probably find the ITU document which details the signal levels and impedance of a standard TTY/TDD designed for cell phones. TTY/TDD mode also changes the way the CODEC operates, which may not be ideal for human voice. But TTY/TDD is a good mode to use for passively recording calls... it generally works quite well with typical home and professional audio equipment line inputs. Just wire up the right cable or connect the equipment with the right adapters.


    Final note: You should use capacitive coupling or inductive isolation if you're making your own patch cable. And use shielded wire... individually shielded is best, but you can use 2-conductor + shield wire if your cable is really short. (If it's too long, you'll get crosstalk from the earphone audio bleeding into the microphone audio).

    Oh yeah... if this all sounds too technical for you, don't mess with it. Ground loops and RF bleeding down the cables could make the phone cause interference with other devices, and that would be bad. Incorrect wiring may also damage the phone or other equipment.

  2. #2
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    Oops, slight correction:

    TTY/TDD mode does not swap the TIP and RING1 connections... I accidentally had those flipped on my workbench when I was trying TTY/TDD mode.

    The impedance and CODEC characteristics do still change though.


    And some further discoveries:

    Turning on Loopset mode causes the Nokia 1100 to use it's built-in microphone capsule for talking, but the headset jack for listening. I haven't had time to test this in-depth yet, but I do believe the Loopset mode is for a low impedance, just like a regular headset.

    And a word of caution... UNPLUG or HANG UP before changing to Loopset mode! If you don't, the phone will squeal and howl with internal feedback until it detects the equipment is disconnected or until the call ends. I think this is from a little firmware glitch.

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    These are really interesting things!
    Are you electriker?

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    What's the proper impedance of the N75?

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    Very Great ideas, Tried it.. Worked

    Thanks alot.
    - Nokia N95
    - Chinese Touch screen+TV
    - Nokia 9300 Communicator
    Nokia 5310 XpressMusic
    - - - - - - Mizah - - - - - -


    -W--W--J--D-

    What Would Jesus Do?
    Just ask yourself that.

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    plz provide circuit diagrams for ease of learning regarding wire connections!

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    Quote Originally Posted by NigelN75
    What's the proper impedance of the N75?
    I don't have an N75 to play with, so I really don't know. If it's from the same era as the 1100, it may be the same.

    I found the EIA/TIA standard for the 2.5mm interface for when the phone is switched to TTY/TDD mode. It's called "TIA/EIA-PN-3-4558-RV1 Rev. A of TIA TSB121". You can download a draft of the standard (in PDF format) here:

    http://ftp.tiaonline.org/TR-45/TR451...0pub%20625.pdf

    It's got all the electrical characteristics (impedance, signal levels, shielding and decoupling tips, etc.) for interfacing to your phone in TTY/TDD mode. It even lists the clearance requirements for a compatible 2.5mm plug! Any modern phone worth it's existance these days should be compliant with this standard.

    If you're planning on interfacing to the phone in normal headset mode or the car hands-free mode, there is no industry defined standard. You'll have to make your interface compatible with whatever Nokia decided for your phone.

    I don't know if there's an industry-defined standard for loopset mode. It really wasn't of interest for my project at the time, because in loopset mode, the phone's internal microphone capsule is still used and only the earphone audio is routed to the 2.5mm jack.

    I can't remember anymore what DC resitances triggered the different modes in my Nokia 1100. That was some time ago.

    If there's enough interest, I'll try to dig up my notes from this project.

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    Quote Originally Posted by taurus3
    plz provide circuit diagrams for ease of learning regarding wire connections!
    It's pretty simple... it's just a matter of choosing whether to use the TIP or the RING conductor of the plug for each audio signal.

    What is it you're trying a build? A simple Nokia-to-defacto-standard headset adapter? Or are you interfacing the phone to some other piece of audio equipment?

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    Quote Originally Posted by shadowman714
    The only reason a standard headset will not work is that standard headsets use the following wiring:

    TIP = microphone (+)
    RING = earphone (+)
    SLEEVE = common microphone and earphone (-)

    If you just swap the TIP and RING (either by rewiring your headset, or making an adapter), it will work. Apparently such adapters are also commercially available.
    To paraphrase the saying, things should be made as simple as possible but not simpler. Not surprisingly, Nokia used a 4 element plug for very solid reasons. While a 3 element plug may work in some cases, it will not work in other cases. Some phones, such as the 6010, use a bridge amplifier configuration to drive the earphone element. The 2 leads are driven 180º out of phase with each other and neither one can be shunted to the ground present on the sleeve element. Doing so will result in squealing due to feedback between the mike and receiver elements.

    It is possible to use a standard headset with 3-conductor plug with these phones if a 1:1 ratio 150-300 ohm audio isolation transformer is inserted in the receiver circuit so that the common connection at the headset plug between mike and receiver is not carried through to the 4-conductor Nokia jack.

    To achieve a workable adapter, of course you need a matching 4-conductor Nokia plug. The best source of this is probably to buy one of the inexpensive Nokia headsets with mike suspended 6" down the cord from the receiver. Since the adapter will have some bulk due to the transformer, clip the cord at least a few feet from the plug so that there is enough cord between the phone and adapter that the phone can be handled conveniently with the adapter placed in a pocket or perhaps attached to the headband of the headset.

    The existing Nokia cord consists of very fine enamel insulated stranded conductors. The strands can be twisted together and tinned, causing the enamel to melt away. Successfully reusing the cord does require some electronic assembly experience and soldering skill.


    Quote Originally Posted by shadowman714
    As some of you may know, modern Nokia phone headsets have 4-conductor plugs, while standard headsets have 3. You may have also found out that plugging a standard headset into a modern Nokia phone does not work.

    After some playing around with my Nokia 1100, I discovered a few cool tricks.

    But first... the information to follow is just from my own experimentation, and may not be entirely accurate. Use at your own risk. I'm not responsible if you do something stupid.

    If you want to connect your own audio devices to a Nokia phone, here's the signal descriptions of the terminals in the phone's headset jack:

    TIP = earphone (+)
    RING1 = microphone (+)
    RING2 = earphone (-)
    SLEEVE = microphone (-)

    You don't have to purchase a rare, hard-to-find 4-conductor 2.5mm plug. A standard 3-conductor one will work for pretty much all your audio connection needs. It's sleeve will just bridge the earphone and microphone negative signals together, which is exactly how standard headsets are wired.

    The only reason a standard headset will not work is that standard headsets use the following wiring:

    TIP = microphone (+)
    RING = earphone (+)
    SLEEVE = common microphone and earphone (-)

    If you just swap the TIP and RING (either by rewiring your headset, or making an adapter), it will work. Apparently such adapters are also commercially available.


  10. #10
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    i'm new to all this not to mention,phone jargon weak but what does unlock your phone mean

  11. #11
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    Excuse me for being silly, but who said standard phone headsets are 3 conductors? It's impossible to make a stereo headset with a microphone with just 3 conductors. Well, okay, not theoretically impossible. But very hard to manage nevertheless.

    Secondly, there are two different kinds of Nokia headsets. The Nokia 5200/5300 headset has some sort of electronics built into it for the radio function on the phone. Some other Nokia phones use standard stereo headsets (4 conductor, of course).

  12. #12
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    Hmmm.On a Nokia 6275i,I'm using a 2$ earpiece-with-mic that I bought at the dollar store.("3 section")Works fine for radio and calls....ok,it's mono,musically but I'm easily pleased.The PopPort earphones (special adapter)are admittedly far better quality sound .
    The "electronics"contained in this?I'm guessing,but they just create and send a tone to the phone which it interprets as a "call-to-action" command.

    Does this mean that a "4 ring" won't work?I haven't found one that does yet but it might be that the exact ring spacing IS critical

  13. #13
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    :P Nokia 5310 works with both 3.5mm jacks (4pin for mic-headset or 3or2 pin standalone headphones) its very sweet its also nice that the headset(4pin 3.5mm) doesn't have a hardwired in headphone it has a 3.5mm jack on it also to let you use any headphones you want and then just clip the mic part to your shirt.

    I love the $10 blue Sony headphones (not adjustable but fit almost anyone they are my favorite)

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    gone try out these ideas the sound good hope they work for me

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    thnxxxxxxx

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