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Rod Whitby
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Working on an even better mounting method for the charging circuit board, including pogo pins between the backplate and the main circuit board. See the captions on the latest photos in the album for details. 
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Nexus 4 Inductive Charging
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Nexus 4 Touchstone Mod (Part 5)
[ Start at Part 1: http://goo.gl/r7ATZ ]

You're looking at the world's first multi-wireless-charging phone, a Nexus 4 that has been modified to support both Qi and Palm Touchstone wireless charging technologies.

Everything is back together, and fully operational (including NFC).  This Nexus 4 phone can now charge on both Qi wireless charging pads and Palm Touchstones, without swapping charging backs or any other inconveniences like that.

Interestingly, the Palm Touchstone seems to charge the Nexus 4 significantly faster than the Qi charger.  I will have to test it on an official Google Orb (not available locally in Australia) to see if that is a limitation of the Qi charger I have, or a limitation of the particular Qi charging circuitry in the Nexus 4.

When placed on the Qi charging pad, the phone shows "Charging (wireless)".  When placed on the Palm Touchstone, the phone shows "Charging (USB)" (because I hooked the Palm Touchstone charging circuit board output internally to the same place to which the USB port VBUS power signal is connected).

Next step is to determine whether I should add magnets inside the back of the phone (like I did on the Galaxy Nexus), or just metal discs.  I will need to test whether the magnetometer in the Nexus 4 is able to automatically compensate (after recalibration) by subtracting the constant magnetic offset caused by the fixed magnets.  Some clipping of the sensor output will obviously occur, but I charge my phone two orders of magnitude more often than I use the compass, so it's a worthwhile trade-off for guaranteed overnight charging without the device slipping off the charging pad.

Guided alignment and guaranteed stability with the magnets in the Palm Touchstone is the key feature that is missing from all current Qi chargers, and is the main thing that makes Qi wireless charging inferior (in my opinion) to using Palm Touchstones.  It seems the Palm Touchstone also has the upper hand in charging time as well (compared to my current Qi charger).

-- Rod
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Nexus 4 Touchstone Mod (Part 4)
[ Start at Part 1: http://goo.gl/r7ATZ ]

The surgery begins ...

See the captions on the attached photos for more information.

[ Continue at Part 5: http://goo.gl/RF8LL ]

-- Rod
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Nexus 4 Touchstone Mod (Part 3)
[ Start at Part 1: http://goo.gl/r7ATZ ]

As expected, clearance of the charging board in the vertical dimension is the killer here.

Not sure how I'm going to solve this one ...

The good news is that the Qi charging still works (electrically speaking, my issue with Qi charging is the lack of physical alignment support on current devices, not the electrical protocol itself) even with the Palm Touchstone coil (and it's Mu-Metal shielding) in place and the cover put back on the phone.  This also confirms that the additional height of the Palm Touchstone coil (as opposed to the charging board) is not a vertical clearance issue.

This may well end up as the only device in existence which is both Palm Touchstone and Qi charging compatible.

See the captions on the attached photos for more information.

[ Continue at Part 4: http://goo.gl/ObRQv ]

-- Rod
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Nexus 4 Touchstone Mod (Part 2)
[ Start at Part 1: http://goo.gl/r7ATZ ]

The next experiment needed before starting any non-reversible modifications is to determine whether the touchstone coil will actually work when located in the Nexus 4 back.

The result of that experiment is surprisingly positive.  It seems that the Qi charging coil in the backplate does not interfere with the operation of the Palm touchstone charging coil.  I was fully expecting to have to remove the Qi coil (hopefully in a replaceable fashion, and without damaging the outer NFC coil) to make this work, but now it seems this is not required.

Now attention turns to the placement of the charging circuit board.  I first looked at the speaker/antenna enclosure at the bottom of the phone (having found those to often contain empty space within the plastic), but there was not joy to be found there.

There does seem to be some room just north of the vibrator motor (in the same vertical plane as the SIM card slot).  It's possible that if a charging board sized section of the plastic shield in that area is removed, then there might just be enough space.  It looks doable in the horizontal plane, it'll be the height of the charging board compared to the thickness of the plastic section removed which will determine success on this step ...

See the captions on the attached photos for more information.

[ Continue at Part 3: http://goo.gl/uZLmZ ]

-- Rod
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Nexus 4 Touchstone Mod (Part 1)

I've decided to add Palm Touchstone charging to the Nexus 4. Qi charging (or at least the physical implementation of it on current devices) is (IMHO) inferior to Palm Touchstone charging. +Derek Kessler seems to agree (http://www.androidcentral.com/i-hate-nexus-4-wireless-charger).

The fact that I have 5 or 6 Palm Touchstones already sitting around my home, car and office, and all the other phones and tablets (see the list at the end of this post) my family uses have already been modified to charge on the Palm Touchstones probably has some influence on my motivations.

I've already done the experiment to ensure that the coil and charging circuit board from Palm Touchstone back has enough voltage and current capacity to charge the Nexus 4.  Only one coil is required.

I have also found a document on the Internet which has enough of the Nexus 4 circuit diagram and PCB component placement details to determine where to inject the 5V into the Nexus 4 (as usual, it's easiest to inject at a point which is electrically equivalent to the standard USB port power pins). Excerpts from that document are attached.

So the big problem is where to situate the small Palm Pre charging board.

There's not a whole lot of spare space inside the Nexus 4, so I'm going to need to get creative ...

[ Continue at Part 2: http://goo.gl/y3WLm ]

-- Rod

Related Links
Nexus S Touchstone Mod: http://www.flickr.com/photos/rwhitby/sets/72157628557489531/
Lumia 800 Touchstone Mod: http://twitpic.com/9jevyp
Galaxy Nexus Touchstone Mod: http://forums.androidcentral.com/verizon-galaxy-nexus-accessories/147840-guide-galaxy-nexus-mod-palm-touchstone-no-soldering-phone.html
Nexus 7 Touchstone Mod: http://goo.gl/2gxd5 
Multi-Charging (Phone and Tablet) Touchstones: http://goo.gl/9c2SL
Other Touchstone capable devices: http://goo.gl/hNyBB
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Four Multi-Charging (Phone and Tablet) Touchstones

These modified touchstones are able to charge my Palm Pre, Palm Pre+, Palm Pixi, Palm Pixi+, Palm Pre 2, HP Veer, HP Pre 3, HP TouchPad, HP TouchPad Go, HP TouchPad 4G, HP WindsorNot, Samsung Nexus S, Samsung Galaxy Nexus, Nokia Lumia 800, and Asus Nexus 7.

See http://goo.gl/VgBha for details of how to build them.

-- Rod
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Nexus 7 Touchstone Mod (Part 13)
[ Start at Part 1: http://goo.gl/2gxd5 ]

Sitting the Nexus 7 directly on the Palm touchstone with no support is not that stable (touching notifications at the top of the screen causes it to tip).

So I came up with a better system.

Now the same HP TouchPad charging dock can charge both the TouchPad and the Nexus 7 (and phones for that matter too).

-- Rod
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Nexus 7 Touchstone Mod (Part 12)
[ Start at Part 1: http://goo.gl/2gxd5 ]

The final result in pictures.

Nexus 7 Touchstone Mod completed successfully.

[ Continue at Part 13: http://goo.gl/VgBha ]

-- Rod
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Nexus 7 Touchstone Mod (Part 11)
[ Start at Part 1: http://goo.gl/2gxd5 ]

I added electrical tape to cover the connections to the coil, and set up for the final soldering of the 5V output from the charging circuitry to the motherboard.

The soldering points are the main GND plane and the main VUSB plane (5V from the USB connector), both of which can be easily exposed near CON 1.  You can test (using a multimeter) that you have the correct points by ensuring that they are connected to 5V and GND on the micro-usb connector.

I scraped the tracks to expose copper, carefully covered the surrounding components, and did the final deed.  This bit is the dangerous part - you need to make sure you don't overheat the motherboard, but those copper planes will suck up the heat and you need to get them hot enough for the solder to make a good connection.

Next is the final assembly and test ...

[ Continue at Part 12: http://goo.gl/KMy8n ]

-- Rod
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