Nokia headset magic

[albertwong]

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).

I will have to say that all the standard stereo headphone are using 3 pin connectors. One for left, one for right and one is ground.

Secondly, there is no special electronic inside the headset for the radio function. Nokia design the phone in such a way that only when you connect a headset to the phone can you hear the radio. The reason behind this is that you need an FM antenna for the radio to work. The headset is the antenna. It is just using the impedence sensing trick to found out if you have connected the headset or not.

[albertwong]

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

Since the nokia phone is using mono for audio. You can easily make a connector.
If your phone has a 2.5mm jack, then the easier way is to purchase a 2.5mm to 3.5mm extension cable and do your connections.

Connect the tip (1)to left and right +ve; connect the following ring(2) to nothing; connect the sleeve (3) to -ve of left and right.

Then with this adapter, you can use any regular earbud.

[fairen]

This is really interesting! I might try this one of these days. Thanks for sharing

[Jam08]

Had this work for anyone yet? I am interested, I hope this is working

[Steph10025]

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.
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.

Like many other things we read on the web, this is partially correct information based on assumptions that are without solid basis.

Nokia did not choose a 4-circuit jack and plug just to increase costs. They did it for a very good technical reason. Some Nokia phones use "bridge" type output drivers where the two ends of the receiver element are driven with oppositely phased signals rather than a signal of twice the voltage and ground. This system is helpful where available power supply voltage and hence drive voltage is low. This is why it is used to deliver high power to loudspeakers in 12V automotive audio systems.

In phones such as this, using a 3-circuit plug will short circuit one output driver. This probably will not damage it but it will cause reduction in receive level and in other cases will cause feedback between the microphone and receiver circuits.

Some Nokia phones may use ground return circuits where a 3-circuit headset will work. In other cases an isolation transformer is needed between the 4-circuit jack and any 3-circuit headset that one connects.

I've stated all this before in this forum.

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[gerryalton]

hahaha...nice discussion...some silly questions.. and good reply...

[ebor]

Does anybody know of a commercially produced or have a design for a transformer type adapter that will convert the proprietary Nokia to a "standard" 3 connector headset?

[whacker]

I just recently Googled "Nokia 5230 wired headset adapter" and was directed to the Nokia Europe discussion forum, where a guy was looking for the same thing as me (a commercially made adapter for connecting a mono with mic communications headset with 2.5mm plug to the 3.5mm jack/socket on the 5230), and he discovered Nokia makes a model called the HDA-12 that is essentially for making TTY device connections, but works perfectly for a wired w/mic headset adapter. I was able to find one on sale at J&R Music World in NYC, ordered it, and it's doing the job I needed it to do. So check out the HDA-12 from Nokia. I also have a Nokia 5310 and assume it'll work the same. This is for making the size adaptation, obviously. Standard 3.5mm stereo headsets for music listening do not need an adapter, obviously.

On a slightly different note, two of the first cell phones I owned were the Nokia 6010 & the 2610, which have the same earphone connections, a 2.5mm four-conductor jack. Back in 2006 I was able to find a commercially produced adapter (at Target) that allowed the use of the common 2.5mm three-conductor plug used on then-common wired comm. headsets, such as Jabra and Plantronics. I still have it, but it's definitely not on the shelves anymore.

[Steph10025]

Does anybody know of a commercially produced or have a design for a transformer type adapter that will convert the proprietary Nokia to a "standard" 3 connector headset?

If you are referring to communications headset with a standard 3-contact 2.5mm plug such as used by probably every manufacturer other other than Nokia, I can supply a schematic for the one I built.

I mentioned the need for a transformer in an earlier message to this forum so perhaps that's what you're referring to. Apparently this forum allows attachments. If you confirm that what I have is what you're looking for I will attach it to a subsequent message.

I can supply the transformer if you are in the US. I built mine in a small plastic pill vial. You will need a cheap Nokia "freebee" headset to sacrifice to obtain a cord with proper plug attached. If you want me to make you a complete adapter we can discuss that too.

[ebor]

I just recently Googled "Nokia 5230 wired headset adapter" and was directed to the Nokia Europe discussion forum, where a guy was looking for the same thing as me (a commercially made adapter for connecting a mono with mic communications headset with 2.5mm plug to the 3.5mm jack/socket on the 5230), and he discovered Nokia makes a model called the HDA-12 that is essentially for making TTY device connections, but works perfectly for a wired w/mic headset adapter. I was able to find one on sale at J&R Music World in NYC, ordered it, and it's doing the job I needed it to do. So check out the HDA-12 from Nokia. I also have a Nokia 5310 and assume it'll work the same. This is for making the size adaptation, obviously. Standard 3.5mm stereo headsets for music listening do not need an adapter, obviously.

On a slightly different note, two of the first cell phones I owned were the Nokia 6010 & the 2610, which have the same earphone connections, a 2.5mm four-conductor jack. Back in 2006 I was able to find a commercially produced adapter (at Target) that allowed the use of the common 2.5mm three-conductor plug used on then-common wired comm. headsets, such as Jabra and Plantronics. I still have it, but it's definitely not on the shelves anymore.

Thank you very much for your quick reply. I am actually trying to go the other way as you mentioned in the second paragraph. The 4 conductor proprietary Nokia to the a regular 2.5 or 3.5 jack. The purpose is to interface to an aircraft audio panel cellphone jack.

[ebor]

If you are referring to communications headset with a standard 3-contact 2.5mm plug such as used by probably every manufacturer other other than Nokia, I can supply a schematic for the one I built.

I mentioned the need for a transformer in an earlier message to this forum so perhaps that's what you're referring to. Apparently this forum allows attachments. If you confirm that what I have is what you're looking for I will attach it to a subsequent message.

I can supply the transformer if you are in the US. I built mine in a small plastic pill vial. You will need a cheap Nokia "freebee" headset to sacrifice to obtain a cord with proper plug attached. If you want me to make you a complete adapter we can discuss that too.

This is along the lines of what I was looking for. As I mentioned in my post above the purpose is to be able to take the 4 contact Nokia scheme and convert it. I know that the mic and earphone grounds can not be shared. The object is to plug it into and aircraft audio panel that accepts a standard three contact plug for cell phone use. (On the ground only of course) I did see your earlier post about a transformer which to me seems the way to go. If you don't mind sharing a schematic of what you conjured up I would greatly appreciate it.

[Steph10025]

This is along the lines of what I was looking for. As I mentioned in my post above the purpose is to be able to take the 4 contact Nokia scheme and convert it. I know that the mic and earphone grounds can not be shared. The object is to plug it into and aircraft audio panel that accepts a standard three contact plug for cell phone use. (On the ground only of course) I did see your earlier post about a transformer which to me seems the way to go. If you don't mind sharing a schematic of what you conjured up I would greatly appreciate it.

I did not find a sketch so I suppose I just built it on the fly from sketches of the assignments of the Nokia plug elements. So I sketched out a complete diagram and scanned it.

IIRC, the Nokia "junk" headset have a cord consisting of two parallel coaxial leads, one for the mike circuit and the other for the receiver. You'll have to dope that out by making continuity tests once you cut the cord as far from the plug as possible. I suggest leaving 6" at the headset end for possible reuse for who-knows-what.

I used a 600:600 ohm telephone line isolation transformer. However I measured the resistance of the Nokia receiver element at 146 ohms and suppose the actual AC impedance is probably something more like 300 ohms, so the 600 ohm transformer might not be quite ideal but it works well enough and does not introduce gross loss. In any case the transformer needs to have a 1:1 ratio and reasonably low impedance. Once upon a time Radio Shack sold 600:600 ohm transformers but I don't think they do any longer.

The headset you actually use it with must of course deliver appropriate signal levels. I found the typical standard cellphone headsets I have do, but I don't know what your aircraft panel does. It ought to be equivalent if it's intended to connect to a typical 3-conductor headset.

All this said, I don't see where the mechanism is for uploading files. I assumed it would be under the MANAGE ATTACHMENTS button but that only seems to be related to managing files that were uploaded previously. If someone will explain where the UPLOAD function is located I will upload a TIF or PDF.
[IMG]file:///C:/DOCUME%7E1/HP_Owner/LOCALS%7E1/Temp/moz-screenshot.png[/IMG]

[ebor]

I did not find a sketch so I suppose I just built it on the fly from sketches of the assignments of the Nokia plug elements. So I sketched out a complete diagram and scanned it.

IIRC, the Nokia "junk" headset have a cord consisting of two parallel coaxial leads, one for the mike circuit and the other for the receiver. You'll have to dope that out by making continuity tests once you cut the cord as far from the plug as possible. I suggest leaving 6" at the headset end for possible reuse for who-knows-what.

I used a 600:600 ohm telephone line isolation transformer. However I measured the resistance of the Nokia receiver element at 146 ohms and suppose the actual AC impedance is probably something more like 300 ohms, so the 600 ohm transformer might not be quite ideal but it works well enough and does not introduce gross loss. In any case the transformer needs to have a 1:1 ratio and reasonably low impedance. Once upon a time Radio Shack sold 600:600 ohm transformers but I don't think they do any longer.

The headset you actually use it with must of course deliver appropriate signal levels. I found the typical standard cellphone headsets I have do, but I don't know what your aircraft panel does. It ought to be equivalent if it's intended to connect to a typical 3-conductor headset.

All this said, I don't see where the mechanism is for uploading files. I assumed it would be under the MANAGE ATTACHMENTS button but that only seems to be related to managing files that were uploaded previously. If someone will explain where the UPLOAD function is located I will upload a TIF or PDF.
[IMG]file:///C:/DOCUME%7E1/HP_Owner/LOCALS%7E1/Temp/moz-screenshot.png[/IMG]

thanks again for the quick reply. The aircraft is standard 600 ohm so if I can find (I might even have some) a 600 ohm isolation xfmr with a center tap that would match the 300 ohm jack.
My third link from the right in this quick reply box say insert image. Maybe that will do it. thanks again

[Steph10025]

thanks again for the quick reply. The aircraft is standard 600 ohm so if I can find (I might even have some) a 600 ohm isolation xfmr with a center tap that would match the 300 ohm jack.
My third link from the right in this quick reply box say insert image. Maybe that will do it. thanks again

I saw that too but if you click on it it prefaces the entry with "http://" and requires entry of a URL, which would require me to upload the image to a publicly accessible server. The other buttons also assume the same conditions.

I don't have a reasonably convenient way to do that and am not going to spend time learning flickr or one of those photo sharing sites for this purpose. I also do not see any mechanism for Private Messaging whereby we could exchange email addresses without exposing them to the spammers.

And BTW, that link to the file on my local drive resulted from my attempt to paste the image directly into the message body after failing to find any alternative. At the moment I performed the paste operation nothing appeared on the screen but now that I see the public echo I see that a useless URL was included.

Note too that the subject lines in the messages are total BS. I edited the subject line in my reply to "Standard Headset to Nokia Cell Phone Adapter" but it's not displaying that way here. And I just corrected it again.