Alright, it seems like I managed to create a prototype for inductively charging the N9 via the Palm Touchstone stuff.


First of all the usual disclaimer and words of caution:
The things shown here are highly dangerous.
By trying to do anything as described here you will for sure void your warranty.
Furhtermore, you might destroy your precious N9 or even worse cause other severe damage or even harm people.
I am not responsible for anything you do based on the things written and described here. You do everything on your own full responsibility.


Having said that, lets move on.
I currently do not have the time to write a nice, full-fledged article about this so I'll just introduce the very basics. I will upload pictures and more descriptions later on when I find the time.

The general idea is to have the inductive sender deliver ~ +5V. This will then be fed into the N9 via the USB connector. This way all the internal charging logic etc. should be able to do its job. Well, we'll see how this works out.

First of all, the good news is that there is enough room in the N9 to place the Touchstone inductive charging receiver, the cabling, and even a simple diode in it. The diode is for "protecting" the receiver circuit from receiving current from the USB port when an external charger is attached or the N9 is attached to a computer via USB. This way it is possible to inductively charge, charge via an external, wired charger, and use the USB connectivity to tranfer data.
Another good news is that the N9 detects when there is sufficient supply voltage at +5V of the USB connector. Thus, it is not necessary to shorten the data pins to trigger charging anymore (as was needed for the N900). This eases the whole effort a lot. However, it is still a very very delicate undertaking. See post #3 below.
And yet another good news is that there are acutally some maintenance(?) pads on the N9 mainboard that ease the soldering part at least a little bit. This way it is not required to mess with the tiny micro USB connector but it is possible to use these pads instead. The pads have a diameter of approximately 1-1.5mm.


There is some video that shows how to inductively charge the Lumia 800. In this video it is shown that some of the metal part of the inner case is removed for the charger to work correctly.
However, I did not want to remove parts of the case that are potentially needed for maintaining the structural stability. Instead I chose to completely remove the inner metal casing, put the receiver coil beneath it and then insert the metal casing again.
On another note, I also put the four, small metal discs that are used for attaching the cell phone to the sender underneath the interior metal casing.

For a very good and detailed guide on how to disassemble the N9 see the following video:
http://mynokiablog.com/2012/05/22/vi...e-replacement/
Note that I used a hot air gun/fan with a temperature of 180°C to heaten the internal metal casing in order to remove it. This is needed because the internal metal casing is glued into the polycarbonate external case. Also note that this process might take some time and is best done in several steps in order to avoid damage to the internal and external casing as well as the flat ribbon cables.



Edit: Please see post #3. There I explain how I could solve the low current issue. I am leaving the following paragraphs in this post for the sake of completeness.

The placement of the coil in relation to the four small metal discs seems to be very important. Here, it showed that there is only very few space for variation in order to assure the charging works at all.

Generally, I am currently facing the issue that the current delivered by the receiver is very low. Placing the receiver on the sender without any load attached shows a more or less constant voltage of 5.6V (note that the drop off voltage of the diode reduces this volatage to a "more USB friendly" ~5.1V). With no attached load the placement also seems not to be very critical.
However, once a load (in this case the N9) is attached the whole system seems to be more fragile. Generally, somehow the receiver seems to deliver a very low current. I am currently investigating this issue.


This issue of the receiver only delivering very low current has some undesired consequences that affect the overall practicability.
Firstly, the charging is very very slow. At the moment it seems like that this is much too slow for the inductive charging being of any practical use.
Secondly, the supplied current seems to depend on the placement of the receiver on the sender. When the sender is not placed correctly, the power draw by the N9 seems to trigger a failsafe shutdown in the receiver such that charging stops immediately after it had started. This then results in a cycle of the USB being reported attached, removed, attached, etc.
Thirdly, even when the charging current is a little bit more stable the N9 reports that the power supplied by the USB port is too low. However, it continues charging but very slowly.
Finally (for now), even when the placement seems to be good and the device charges very slowly it does disconnect from time to time in intervals of about 5 or 10 minutes.


So far, as you can see this is still very very experimental. While there are some good news that illustrate the general practicability there are still some issues that render the daily usage impractical for now.
Comments and feedback are highly appreciated. Especially hints on how to solve the issue with the low current.
Are there any people that have more experience with the Touchstone charging kit and its specifications?