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Thread: Nokia headset magic

  1. #31
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    Quote Originally Posted by Steph10025 View Post
    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.
    Well thanks for trying. If you figure out the PM I would appreciate it.

  2. #32
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    I sent this message via the CONTACT US page:

    I don't see any way to attach a graphic file. There is a MANAGEMENT button to manage files that were already uploaded but I don't see any way to upload them. There are provisions to include links to files hosted at public URLs but that does not help me.

    I also do not see any way to Private Message people so that people who are trying to help each other can exchange email addresses privately and send diagrams directly to the people they are helping.

    Please provide a solution to this problem.

    Thanks.
    (user name)

  3. #33
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    Standard Headset to Nokia Cell Phone Adapter

    Diagram attached. Please let me know how it works out.
    Attached Images Attached Images

  4. #34
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    Quote Originally Posted by Steph10025 View Post
    Diagram attached. Please let me know how it works out.
    I will definietely give it a shot at some point this week. I know you went to a lot of trouble to get this to me so I want you to know I appreciate it. I will let you know as soon as I have it put together.

  5. #35
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    Thanks for letting me know. You sounded appreciative and therefore deserving. That's why I made the effort. Hope it works for you. If not, it ought to work with some modification. The concept is correct.

  6. #36
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    Quote Originally Posted by Steph10025 View Post
    Thanks for letting me know. You sounded appreciative and therefore deserving. That's why I made the effort. Hope it works for you. If not, it ought to work with some modification. The concept is correct.
    Your circuit works fine. I had a discussion about it with an avionics technician and he reccomended one step further. His suggestion was to use two transformers, one for each element. The reason being is he was afraid if you tried to get DC power from the aircraft itself (via the accessory jack) to power the phone ground loops could possibly develop. This would eliminate that possibility. Thanks again for your time and effort.

  7. #37
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    Nokia/Aircraft audio & power connections

    Quote Originally Posted by ebor View Post
    Your circuit works fine. I had a discussion about it with an avionics technician and he reccomended one step further. His suggestion was to use two transformers, one for each element. The reason being is he was afraid if you tried to get DC power from the aircraft itself (via the accessory jack) to power the phone ground loops could possibly develop. This would eliminate that possibility. Thanks again for your time and effort.
    Good! You're welcome.

    Because this message has become so long I've switched to composing it in Notepad and pasted it into the window. Let's hope that does not result in a lot of orphan lines. If it does we'll understand why they're there. The message may also get truncated when I paste it due to length. We shall see!

    You didn't mention that you intended to power the phone from the aircraft. There are a number of potential major problems with that which the technician may not be aware of.

    In the first place if you look at my diagram you will notice that the microphone circuit is marked with polarity symbols. That's because electret mikes such as used in light weight headsets require a tiny DC power supply from the input circuit. Even the MIC jacks on the very first Sound Blaster boards for PCs provided this. You cannot isolate the mike circuit with a transformer without blocking this DC supply to the mike, in which case you would need a few batteries such as LR44s in the adapter to power the mike. That would be a nuisance. You would have to be sure to unplug the headset when not in use to prevent running them down. So you might be better to isolate the power supply circuit instead even though it might be more complex. Obviously this reflects my own prejudice against using batteries where avoidable even if it means more complexity.

    I suggest you first determine whether there's a problem and how severe it is by connecting the phone to the aircraft headset jack using the adapter you built and checking to see whether you read DC voltage between any of the Nokia power jack connections and the aircraft power supply. If so that means there is no isolation of the audio in the aircraft.

    It seems prudent to me for the aircraft audio to be isolated from the rest of the aircraft's power and ground for noise reasons. But it might not be and connecting to both power and the headset circuit could not merely introduce a ground loop but actually put a relatively unlimited amount of current through the phone, destroying it.

    Isolation of the power supply, if necessary, can be done using a small DC-DC converter if you can determine the proper specs. But that may not be so easy. It's not certain whether the charging control circuit for any given cellphone is in the cell phone itself or in the external charger, be that an AC power line charger or a vehicle cigarette lighter adapter. If the charging control circuit is in the adapter and you don't reproduce its function accurately you may destroy the phone and/or the battery. I've seen phones that used both methods. So while it's likely that any modern charging adapter contains a DC-DC converter, it's not a certainty whether the charger or the phone controls the charging and whether the DC-DC converter in the vehicle charging adapter is isolated from input to output.

    The Nokia AC line chargers I've seen do use isolated switching converters which have tightly regulated outputs but I don't know for sure where the charge regulation is done. AC adapters which use switching converters are easily recognizable by their very small size and light weight relative to ones that use a 60Hz transformer. And AC chargers must be isolated to prevent a shock hazard. Vehicle chargers don't necessarily need to be.

    Since the location and requirements of the charging circuit are probably going to be difficult to determine and the Nokia vehicle chargers itself might contain an isolated DC-DC converter, that would be the safest thing to use if the aircraft has a lighter socket. But first you need to determine whether the Nokia vehicle charger is actually isolated by performing resistance tests between the output jack conductors and the cigarette lighter plug side of the charger or by plugging it into a vehicle and testing for voltage between the output plug of the Nokia charger and the vehicle chassis.

    You should measure zero volts to both elements of the Nokia charger output plug relative to the vehicle chassis. An automobile is a perfectly valid environment for this test. If the aircraft does not have a cigarette lighter socket but 12V is in fact available and tests demonstrate that the Nokia charger is in fact isolated, using the Nokia adapter would by far be the most prudent solution. Buy a cigarette lighter socket at Radio Shack, such as a cord mounted one that does not require drilling a hole for mounting and which is fully insulated. Connect it to a fused 12V source in the aircraft.

    If the aircraft operates at 24V and there is no 12V source available, a surplus 24V/12V DC-DC converter can be easily found to convert the aircraft voltage to what the Nokia needs. Since the charging control would still be performed by the Nokia adapter, the issues that would arise using a DC-DC converter directly without the Nokia adapter would not arise in this case with the two in tandem. It's also possible for the small amount of power the Nokia phone needs to be obtained using a simple resistor and shunt zener regulator to drop the aircraft power to 12V. We'll cross that bridge if we arrive there.

    Let me know which of these possibilities plays out and makes sense.
    Last edited by Steph10025; 11-11-2010 at 05:14 AM.

  8. #38
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    Quote Originally Posted by Steph10025 View Post
    Good! You're welcome.

    Because this message has become so long I've switched to composing it in Notepad and pasted it into the window. Let's hope that does not result in a lot of orphan lines. If it does we'll understand why they're there. The message may also get truncated when I paste it due to length. We shall see!

    You didn't mention that you intended to power the phone from the aircraft. There are a number of potential major problems with that which the technician may not be aware of.

    In the first place if you look at my diagram you will notice that the microphone circuit is marked with polarity symbols. That's because electret mikes such as used in light weight headsets require a tiny DC power supply from the input circuit. Even the MIC jacks on the very first Sound Blaster boards for PCs provided this. You cannot isolate the mike circuit with a transformer without blocking this DC supply to the mike, in which case you would need a few batteries such as LR44s in the adapter to power the mike. That would be a nuisance. You would have to be sure to unplug the headset when not in use to prevent running them down. So you might be better to isolate the power supply circuit instead even though it might be more complex. Obviously this reflects my own prejudice against using batteries where avoidable even if it means more complexity.

    I suggest you first determine whether there's a problem and how severe it is by connecting the phone to the aircraft headset jack using the adapter you built and checking to see whether you read DC voltage between any of the Nokia power jack connections and the aircraft power supply. If so that means there is no isolation of the audio in the aircraft.

    It seems prudent to me for the aircraft audio to be isolated from the rest of the aircraft's power and ground for noise reasons. But it might not be and connecting to both power and the headset circuit could not merely introduce a ground loop but actually put a relatively unlimited amount of current through the phone, destroying it.

    Isolation of the power supply, if necessary, can be done using a small DC-DC converter if you can determine the proper specs. But that may not be so easy. It's not certain whether the charging control circuit for any given cellphone is in the cell phone itself or in the external charger, be that an AC power line charger or a vehicle cigarette lighter adapter. If the charging control circuit is in the adapter and you don't reproduce its function accurately you may destroy the phone and/or the battery. I've seen phones that used both methods. So while it's likely that any modern charging adapter contains a DC-DC converter, it's not a certainty whether the charger or the phone controls the charging and whether the DC-DC converter in the vehicle charging adapter is isolated from input to output.

    The Nokia AC line chargers I've seen do use isolated switching converters which have tightly regulated outputs but I don't know for sure where the charge regulation is done. AC adapters which use switching converters are easily recognizable by their very small size and light weight relative to ones that use a 60Hz transformer. And AC chargers must be isolated to prevent a shock hazard. Vehicle chargers don't necessarily need to be.

    Since the location and requirements of the charging circuit are probably going to be difficult to determine and the Nokia vehicle chargers itself might contain an isolated DC-DC converter, that would be the safest thing to use if the aircraft has a lighter socket. But first you need to determine whether the Nokia vehicle charger is actually isolated by performing resistance tests between the output jack conductors and the cigarette lighter plug side of the charger or by plugging it into a vehicle and testing for voltage between the output plug of the Nokia charger and the vehicle chassis.

    You should measure zero volts to both elements of the Nokia charger output plug relative to the vehicle chassis. An automobile is a perfectly valid environment for this test. If the aircraft does not have a cigarette lighter socket but 12V is in fact available and tests demonstrate that the Nokia charger is in fact isolated, using the Nokia adapter would by far be the most prudent solution. Buy a cigarette lighter socket at Radio Shack, such as a cord mounted one that does not require drilling a hole for mounting and which is fully insulated. Connect it to a fused 12V source in the aircraft.

    If the aircraft operates at 24V and there is no 12V source available, a surplus 24V/12V DC-DC converter can be easily found to convert the aircraft voltage to what the Nokia needs. Since the charging control would still be performed by the Nokia adapter, the issues that would arise using a DC-DC converter directly without the Nokia adapter would not arise in this case with the two in tandem. It's also possible for the small amount of power the Nokia phone needs to be obtained using a simple resistor and shunt zener regulator to drop the aircraft power to 12V. We'll cross that bridge if we arrive there.

    Let me know which of these possibilities plays out and makes sense.
    I think the simple solution is to forget the idea about using onboard power and just rely on the battery. If it needs to be charged in flight for any reason (which it probably won't) the simple solution is to pull the headset plug while its charging, You have put a lot of thought into this and I think your pointing out the pitfalls overshadows any advantages gained from trying to complete the isolation with power. You've been a great help and resource so please know that it has been greatly appreciated. If you get around the Atlanta area drop me a note and let's do some flying.

  9. #39
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    Quote Originally Posted by ebor View Post
    I think the simple solution is to forget the idea about using onboard power and just rely on the battery. If it needs to be charged in flight for any reason (which it probably won't) the simple solution is to pull the headset plug while its charging, You have put a lot of thought into this and I think your pointing out the pitfalls overshadows any advantages gained from trying to complete the isolation with power.
    Yes, the added complexity may not be worth the effort if the amount of use is low enough for the batteries to handle it.

    Nevertheless I'm curious to know what arrangements exist to charge the cellphone from the aircraft electrical system. Would that be done using a cigarette lighter socket and Nokia vehicle charger or is there some other provision in the aircraft?

    Quote Originally Posted by ebor View Post
    You've been a great help and resource so please know that it has been greatly appreciated. If you get around the Atlanta area drop me a note and let's do some flying.
    You're welcome and thanks for the invitation. Realistically, it's unlikely I will find myself in Atlanta but if I do I will keep you in mind.

  10. #40
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    Quote Originally Posted by Steph10025 View Post
    Yes, the added complexity may not be worth the effort if the amount of use is low enough for the batteries to handle it.

    Nevertheless I'm curious to know what arrangements exist to charge the cellphone from the aircraft electrical system. Would that be done using a cigarette lighter socket and Nokia vehicle charger or is there some other provision in the aircraft?


    You're welcome and thanks for the invitation. Realistically, it's unlikely I will find myself in Atlanta but if I do I will keep you in mind.
    Just a regular cigarette lighter.

  11. #41
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    Quote Originally Posted by ebor View Post
    Just a regular cigarette lighter.
    In that case I think you ought to determine whether your Nokia charger is isolated. It's not difficult to do that and if it is (I would not be surprised if it were) you can safely use it. If it's not... well then you know you must run the phone on its battery.

  12. #42
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    Quote Originally Posted by Steph10025 View Post
    In that case I think you ought to determine whether your Nokia charger is isolated. It's not difficult to do that and if it is (I would not be surprised if it were) you can safely use it. If it's not... well then you know you must run the phone on its battery.
    I'm going to take the simple way out and just go with the battery. Thanks again for all your help.

  13. #43
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    Yeah, some are fun, some seems wired, some seems amazing. I have updated my headsets to 4-conductor plugs nowadays. But if I Knew a standard 3-conductor one will work for pretty much all my audio connection needs, I should have been using my that old 3-conductor now!

  14. #44
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    Quote Originally Posted by ebor View Post
    I'm going to take the simple way out and just go with the battery. Thanks again for all your help.
    As you wish. You're welcome.

  15. #45
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    Yeah, some are fun, some seems wired, some seems amazing. I have updated my headsets to 4-conductor plugs nowadays. But if I Knew a standard 3-conductor one will work for pretty much all my audio connection needs, I should have been using my that old 3-conductor now!

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