A Blog Less Ordinary

The blog of Dave Ingram

Hearing aid direct audio input

Many hearing aids can handle direct audio input (DAI), often via a “shoe” that attaches to contacts on the aid itself. This shoe then provides a DAI jack (sometimes called a europlug or eurojack) that cables can be plugged into.

There seems to be a complete lack of cables designed for people with a single hearing aid, so one of my upcoming projects will be to convert a Y-cable that can serve two hearing aids into a joint DAI/earphone cable instead.

DAI connector pinout

DAI connector pinout

The DAI connector has the following pinout:

Remember that a standard 3.5mm audio plug has the following pinout:

Next stage: connecting an earphone to the plug on one side of the cable, to see if there are any impedance issues, although the cable I am using (an fmGenie one) is a very low-impedance cable because I have an Oticon hearing aid. Measured with a multimeter, it seems to be around 0?, so I think that’s good enough for me. I believe attenuated cables have a 330k? resistor in series with each signal line (according to Neil Ferguson’s bluetooth hearing aid hack page).

My ultimate goal is to get hold of a DAI jack that I can solder directly to an old earphone, so that I can just plug the spare DAI cable into the earphone directly, almost as if it were a hearing aid itself. Unfortunately, it seems that it is impossible to get hold of such things. According to Connevans, DAI jacks are only custom-made for hearing aid shoes. After some discussion, it seems like I should be able to make one myself though (with some help!) so we shall have to see how that turns out.

One Response to Hearing aid direct audio input

Kevin says: April 14, 2011 at 16:07

Hi there did you have any luck with making the cable? Or finding someone to make the cable as i am interested to know this. Thanks

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