Bluetooth Headsets & Hearing Aids
THE INFORMATION ON THIS PAGE IS PROVIDED 'AS IS', WITH NO WARRANTY OF ANY KIND WHATSOEVER. I ACCEPT NO RESPONSIBILITY FOR ANY INJURIES, LOSSES OR DAMAGES YOU MAY CAUSE OR INCUR AS A RESULT OF YOUR USING THE INFORMATION ON THIS PAGE. YOU ACCEPT SOLE RESPONSIBILITY FOR YOUR ACTIONS IN RELATION TO THE INFORMATION ON THIS PAGE, AND FOR ALL CONSEQUENCES THEREOF.
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ELECTRONIC ASSEMBLY WORK SHOULD ONLY BE CARRIED OUT BY SUITABLY QUALIFIED INDIVIDUALS. IT CARRIES RISKS INCLUDING BUT NOT LIMITED TO THOSE OF PERSONAL INJURY AND DAMAGE TO PROPERTY. SUCH RISKS MAY BE DIRECT OR INDIRECT.
THE BLUETOOTH HEADSET CONVERSION DESCRIBED ON THIS PAGE HAS ONLY BEEN TESTED BY ONE PERSON WITH ONE TYPE OF HEARING AID. IT IS NOT GUARANTEED TO WORK FOR YOU WITH YOUR HEARING AIDS.
It is now possible to buy Bluetooth headset modules for hearing aids on a commercial basis. My congratulations to Starkey for making it happen. You can learn more about their ELI system here.
I-Tech make devices which offer Bluetooth connectivity and output via standard headphone sockets. You can see examples by going here - try clicking on the "Clip R35" or "Clip S35". You can find links to the user manuals at the lower right corner of the product windows.
Whilst writing this page, I came across several related products for hearing aid users. You can find these in the "Alternatives" section at the end of the page.
There is a community called Hearing Aid Hacking on LiveJournal which was founded to let people discuss technological solutions to hearing loss. I'm one of the maintainers, and we have about 150 members, so we can bring quite a lot of knowledge and experience to bear. All discussions are public, including the archive, and you're welcome to join us.
Although this page may not be as relevant to you as it used to be, I'll leave it in place for the benefit of anyone who might like to build their own headset module.
Many of you who read this will be only too aware of the way a mobile telephone can render a hearing aid useless by way of radio frequency interference (RFI). Of course, the closer the phone gets to the hearing aid, the worse the problem becomes, and by the time it's next to the aid, virtually nothing but the RFI is audible. As a result, hearing aid users are generally excluded from using mobile telephones for voice calls, although SMS has proven popular as a partial alternative.
Naturally, people always try to find ways to get around problems like this. Some are lucky enough to be able to take their hearing aid out and compensate with the phone's volume control. Others have relatively RFI-resistant hearing aids, so that they can use the hands-free induction couplers produced by the more attentive manufacturers. These devices let the user keep the phone a metre or so away from the hearing aid, thus attenuating the RFI.
Unfortunately, my hearing loss is sufficiently severe that neither of these workarounds is an option. For a verbal conversation where I can't lipread the other person, I must have the 80 decibels of frequency-dependent boost that my hearing aids provide. Taking them out is not an option, and using such powerful amplification means that the hearing aid can clearly receive RFI from a mobile phone two metres away. No amount of extension cable will make a wired hands-free usable - the wire always conducts enough RFI to cause trouble, regardless of any filters that might be in place.
I do have some advantages, however - I'm an electronic engineer, and I've been thinking about this problem for quite some time now. As a recent graduate working for an Ericsson R&D unit in 2000, I was present for one of the first technical presentations on Bluetooth. Among other things, I learned that Bluetooth headsets produce much lower power radio emissions than a mobile handset. The difference can easily be two orders of magnitude. Bluetooth modulation schemes are also rather less perceptible to the human ear as interference.
A few weeks later, our management asked us to suggest new products as part of a patent-related bonus scheme, and I put two and two together. I wrote up a proposal for a Bluetooth module that could talk to a hearing aid, which wasn't patentable, along with some advanced developments that were. That proposal was subsequently accepted for evaluation, earning me the princely sum of £50.
By now, it was early 2001, and the telecoms crash was getting underway. One consequence of that was the sale of our department to another company - painful, but a much better option than redundancy. The intellectual property remained with Ericsson, however, including my proposal. With little spare cash for new projects, and no one left to sponsor it, the Bluetooth hearing aid adaptor disappeared into limbo.
That wasn't the end of the story, however. Although I couldn't develop the patentable ideas I'd handed over to Ericsson, there was no reason why I shouldn't try to create the basic device that would let hearing aids use Bluetooth. After all, the principle was simple - all I had to do was swap the earpiece on the headset for a hearing aid compatible audio connector. The basic function of the device would remain exactly the same. In patent jargon, exchanging a standard earpiece for an equally standard audio socket is not an "inventive step".
Naturally, the fully-integrated on-ear headsets that dominate the market are useless for this purpose, since they require the space already occupied by a hearing aid. Although I did experiment with various bits of hardware, I effectively had to wait for the industry to diversify its offerings. After a while, clip-on Bluetooth modules appeared with Walkman-style earpieces on flying leads, driven by demand from people who find an on-ear unit uncomfortable to wear. Those clip-on modules can be adapted for hearing aids.
After a false start with a different brand, I eventually selected the I-Tech Bluetooth Clip as my starting point. This unit has various advantages:
The following two sections of this page describe the process of making a Bluetooth Clip work with my hearing aids in more detail. Naturally, the patentable ideas I wrote up for Ericsson are not disclosed, as they remain Ericsson property.
For your convenience, I've included approximate prices, with links to the suppliers I used to buy the parts I needed for this conversion. They aren't the only suppliers out there, though, so you might want to shop around.
Note: The type and number of these parts will depend on the type and number of your hearing aids.
The total cost should be well under £100. I already had the Connevans parts to use with my portable CD player, so the extra cost to me was actually less than £35.
The first step in this conversion was to discover exactly how the Bluetooth Clip's flying lead was wired. From the outside, one can see that the lead only has an earpiece on it, with a single pushbutton switch built into the outer surface of the earpiece.
Figure 2 shows that I-Tech took the sensibly low-complexity option of wiring everything separately, with two cores each for the earpiece and the switch. The red and green (R + G) pair connect to a standard 32Ω Walkman-style earphone transducer. The blue and copper (B + C) pair connect to the switch, which is a momentary-on pushbutton type. Polarity does not seem to be important for either core pair.
The individual cable cores are extremely thin - 0.25mm or less. This means that they are easily broken. To save space, each core is lacquered for insulation, with an outer plastic shell binding them all together with some nylon reinforcing strands. When soldering to the cores, the lacquer needs to be burned off with a soldering iron before the solder will bond to the copper. You'll need to clean the iron rather often...
As the original switch is built into the earpiece, and the earpiece has to be cut off and discarded, a replacement switch is required. I used one which was suitably sized to fit inside the insulating boot from a 3.5mm audio socket, thus ensuring protection for the connections and a reasonably neat look. See Figure 3, above.
To ensure that the switch contacts would remain insulated from each other, I coated them in gel-based superglue prior to assembling the switch unit. The switch itself is then superglued into the insulating boot, and the cable is superglued to the strain relief grommet. The advantage of gel-based glue is that it can be adjusted for a short period, before it sets. Figure 4 shows the completed assembly.
As the cable cores are so thin, making the necessary connections to the Bluetooth Clip is a fiddly business. The easiest way to do it is by soldering the green audio core to the 3.5mm audio socket's shield contact. The weight of the connector helps keep everything still for the following stages.
Assuming you've remembered to thread the insulating boot onto the Bluetooth Clip's cable before soldering anything - I didn't, at the first attempt - you should now have something like Figure 5. The next step is to solder the red audio core to one (mono) or both (stereo) of the 3.5mm socket's signal contacts.
To add the switch assembly, its cable should be threaded through the 3.5mm socket's insulating boot - from the Bluetooth Clip's end - before soldering the switch leads to the blue and copper cores. This will let you hide all four of the connections to the Bluetooth Clip inside the insulating boot.
Once the soldering has been completed, I recommend using more gel-based superglue to both insulate everything and make sure it will never move again. Metal fatigue won't take long to break those cores, otherwise. Unfortunately, I forgot to take a photo before I'd glued everything up, so there's no figure showing all four cores in place prior to final assembly.
Once the glue dries, your Bluetooth Clip is ready for use - Figure 6 shows what mine looked like on completion. I advise you to pair the Clip to your mobile handset first, without plugging it into your hearing aids.
If that works, plug Walkman earphones into the Clip, and set your hearing aid to 'T' or induction loop mode. While holding an earphone to your hearing aid, you should be able to hear the beep the Clip makes when you switch it on. If not, find a friend who can use the earphone direct. If that fails, you'll need to figure out what's wrong and fix it - unfortunately, that probably means cutting the audio socket off and starting again.
From here on, the manuals that come with your handset and the Bluetooth Clip should cover everything you need to know. Welcome to the world of mobile voice calls!
The converted headset has worked perfectly for me so far. As long as my handset is at least two metres away, I cannot hear any RFI whatsoever. That doesn't mean there isn't any, though. My hearing is pretty bad at any frequency, and it peters out completely at about 8kHz, where normal hearing can extend to 20kHz. The headset could be beaming signals to Mars somewhere above 8kHz, and I would never know...
I'm currently working on getting the headset to talk to a fixed-line telephone, using a Bluespoon Home connection kit. The Bluespoon doesn't seem to like the I-Tech headset, however, so I haven't been able to make it work yet. I've started a thread on the Expansys Technical Support Forum discussing the issue, and you can follow it here.
For the record, I used an Ericsson T68 handset for this project, and two BE56D MK3 hearing aids issued by the British National Health Service.
There are many ways in which the conversion described above can be improved. Unfortunately, most of my ideas on the subject are already owned by Ericsson, so I can't comment on those.
That said, there is one point I'd like to make here. You've seen how simple it is to convert the Bluetooth Clip to use a different type of audio connection. If you look at Figure 7, you'll see the connectors on the Connevans hearing aid adaptor cable.
The gold three-pin connector is standard within the hearing aid industry. It provides a single connection to any type of Direct Audio Input (DAI) shoe - you can see one of mine to the left of the connector - so that each hearing aid can have its own form of shoe which matches that hearing aid's particular shape.
Ask yourself - why hasn't the mobile communications industry made Bluetooth headsets available with hearing aid protection circuitry and DAI connectors built in?
These things aren't complicated - Connevans sell the adaptor cable for less than £20. So far, it's been almost 4 years since I first learned about Bluetooth, and no-one has done it yet.
If you would like to see the mobile communications industry create hearing-aid compatible products, the only way to make it happen is to draw as much attention as possible to this forgotten segment of the market. Manufacturers will not take the risk of making a product until they know that a market exists. Make yourself heard - contact the appropriate companies and tell them what products you need!
Please feel free to forward the address of this page to anyone you think should see it. In addition, you may publicly mirror this page in its entirety for non-profit purposes, provided that you accept my right to revoke your permission to do so at any time.
NOTE: The blue 3.5mm stereo audio plug on the Connevans adaptor cable (Figure 7) is obviously standard in form. However, it contains protective circuitry for the hearing aids it connects to. The exact form of that circuitry varies between manufacturers. If you experiment with such circuitry, be careful. Figure 8 is a schematic describing the Connevans adaptor cable I have (also available as an EPS file to print).
It is now possible to buy Bluetooth headset modules for hearing aids on a commercial basis. My congratulations to Starkey for making it happen. You can learn more about their ELI system here.
NOTE: I often give Connevans product links, simply because they're my usual supplier, but there must be other sources out there. Relevant links to alternative products are welcome. Please also let me know if any of my links become broken!
If your hearing aids are relatively immune to RFI, and you feel no particular need for Bluetooth with your mobile phone, you might want to investigate products like these:
If you prefer induction loopsets to DAI connectors, you may still be able to make use of a converted Bluetooth headset. Try modifying it as described within this page, but plug something like this or this into it instead.
I-Tech make devices which offer Bluetooth connectivity and output via standard headphone sockets. You can see examples by going here - try clicking on the "Clip R35" or "Clip S35". You can find links to the user manuals at the lower right corner of the product windows.
GN ReSound have a Bluetooth headset with an induction coupler for hearing aids with a 'T' setting. However, DAI connections are usually better than induction couplers, because the induction pickup has a nasty habit of receiving mains hum and electronic interference, in addition to mobile phone RFI!
Phonak make a Bluetooth enabled FM transmitter for their range of FM receivers. These look very nice - the receivers are sugar cube sized, plug into a DAI shoe, and draw power from the hearing aid battery. Unfortunately, such a system will set you back by several hundred pounds.
You can buy most of the Phonak range from Connevans, and the SmartLink should appear there when it comes to the UK. For those of you who can use them, wired handsfree units with induction couplers are available, along with a wide selection of other hearing aid related products.
The proposals on this page go much further than anything I have here. The author's vision for combining hearing aids and Personal Area Networks (such as Bluetooth) is impressive. A system like this could open up a remarkable range of possibilities for people with hearing losses.
If you're interested in building your own induction loops for use with hearing aids, this page from Marc's Technical Pages could well be useful. Look under "Audio" in the left hand frame.
This page was featured in an article on Slashdot [discussion now archived].
There is a community called Hearing Aid Hacking on LiveJournal which was founded to let people discuss technological solutions to hearing loss. I'm one of the maintainers, and we have about 150 members, so we can bring quite a lot of knowledge and experience to bear. All discussions are public, including the archive, and you're welcome to join us.
I used to provide an email address here, but the immense volume of spam has forced me to deactivate it. Please see "Discussion Areas" above for places where you can talk about projects like this, and much more besides.
All trademarks mentioned within this document are the property of their respective owners.
This page is copyright ©2004-2008 Neil Ferguson.
Please feel free to forward the address of this page to anyone you think should see it. In addition, you may publicly mirror this page in its entirety for non-profit purposes, provided that you accept my right to revoke your permission to do so at any time.