Thread: Nokia Head Set Magic
Nokia Head Set 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.
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Re: Nokia Head Set Magic
thanks to share that but i have a Question from Admin. how i can connect my mobile to my PC wich software will be used to connect.
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