Epic 4G Touch-stone mod

Honis#WP

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Well, to try and get my mod working I introduced about a 1ohm resistance between VCC off the coil and the USB port. The max amperage from the Samsung AC/DC adapter is 1Amp so it dropped the voltage about 1V to roughly 4.6Volts into the phone. I measured to confirm the drop. I still got a wonky touch screen.

Doing some retesting at this lower voltage, the digitizer problem is most assuredly from the static magnetic fields coming from the TouchStone. Removing the stubs/magnets from around the coil greatly reduces the range of the effect. When they're in place they are extending the magnetic field which makes it all that much closer to the screen/digitizer.

These magnetic fields are not absorbed by a Faraday cage because they are static (think bar magnet and metal filings). The magnetic field coming off the coil is blocked because it oscillating magnetic fields (think of a sine wave) which are blocked by Faraday cages (the metal tetris piece is providing the blocking in 1 direction).


Knowing all of that I'm putting a close on my project. I don't want to take a TouchStone apart to remove the alignment magnets because there will only be friction from weight holding it in place and I'm thinking there will be more forgiving devices than my GS2 that this can be added too. (PSP, PS3 controllers, a DS, etc.)
 
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darrenf

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-Roninlb, as Honis said, as long as your case isn't too thick and doesn't have metal in it you should be fine. If the back has some grip that will help it stick to the Touchstone. The Pixi back is a good bit thicker than the Pre's but still works. Please report back on your progress!

-Honis,

I have a couple more data points to evaluate should you decide to continue research with me on the digitizer issue. The digitizer works fine when the phone is on the touchstone in my car, with an audio plug connected, playing podcasts. The improvement isn't caused strictly by the connection of the headphone cable -- I have to have loaded the CPU a little. In a separate test, the digitizer works fine when the charging cycle is complete or nearly complete (>~98%), even at idle.

My hypothesis is this:

When nearing a full charge, the phone starts to trickle charge, which reduces the current through the charging coil (similar to the effect you got with the phone off-center of the Touchstone). It makes sense that this would lead to a weaker RF field around the coil which we are assuming is related to the problem.

What complicates this is that with the phone charging at 50%, the digitizers work if the CPU is loaded. I suggest two possibilities:

1. Higher heat in the phone causes the charging circuit to slow the charge, or

2. The increased load means that a percentage (more than half in this test) of the charging current is powering the phone, which means that only half as much current is going into the charging of the battery.

Theory 1 makes good sense but didn't correlate 100% with my observations. #2 does, but means that the problem is a combination of high-current through the *charging circuit built into the E4GT* in the presence of the charging coils (because at a distance from the coils the effect goes away).

This is all observational from one long drive home. I'll do some testing on the bench to see if I can narrow the cause.

One other issue has me puzzled and it's not related to the digitizer but rather to the studs/magnets on the phone that center it on the Touchstone. I have eight charging backs, some old and some unopened. Most are from Pres and one is from a Pixi. I picked a sample of four of them to test out tonight and not one of them has magnets in those four points around the coil.

I pulled a stud out from each and tested it with the lightest ferrous things I could find, including metal filings from sawing on a piece of iron pipe, and got no attraction to either side of the stud. They are marked with a plus or X so it makes sense that they would be polarized, but unlike in your test I'm able to position them on the touchstone and then flip them over and they snap back to the *exact* same place. Also, all of mine were manufactured with the plus towards the *inside* of the phone and I think you said that yours didn't work in that arrangement.

Particularly perplexing to me is the video you linked to of the external touchstone mod. In that example, he definitely has magnets -- they all but jump out of his hand and stick to the phone (which, by the way, I would not have expected to be made of a ferrous metal).

All I can guess is that the design of these studs was changed at some point along the way. Perhaps magnets were used in some models to get a better grip on the Touchstone. Very odd. Not really significant, but odd.

-darren
 

darrenf

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Hows the charge speed?

I used the touchpad charger for the g s2 tonight, seemed to speed up the process quite a bit vs stock.

Charging speed seems on par with a 1A charger wired straight in. There should be some loss because induction coils aren't known for efficiency, but in my tests with my Touchstone modded Nexus S 4G, I found that I got more or less the same charging rate with the touchstone as when I removed the 1A 5V supply line from the Touchstone and plugged it straight into the charging port on the phone. Being a Nexus S 4G, of course, the charging rate was terrible in both cases. :)

Interestingly, tonight I charged my E4GT for a bit with an external battery pack that said it put out 1.5A. The phone went from 2% to 50% in 70 minutes. Nice! It's good to know that it will charge that fast in a pinch if I have to bring it back from the dead!

-darren
 

Honis#WP

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-Honis,

I have a couple more data points to evaluate should you decide to continue research with me on the digitizer issue. The digitizer works fine when the phone is on the touchstone in my car, with an audio plug connected, playing podcasts. The improvement isn't caused strictly by the connection of the headphone cable -- I have to have loaded the CPU a little. In a separate test, the digitizer works fine when the charging cycle is complete or nearly complete (>~98%), even at idle.

My hypothesis is this:

When nearing a full charge, the phone starts to trickle charge, which reduces the current through the charging coil (similar to the effect you got with the phone off-center of the Touchstone). It makes sense that this would lead to a weaker RF field around the coil which we are assuming is related to the problem.

What complicates this is that with the phone charging at 50%, the digitizers work if the CPU is loaded. I suggest two possibilities:

1. Higher heat in the phone causes the charging circuit to slow the charge, or

2. The increased load means that a percentage (more than half in this test) of the charging current is powering the phone, which means that only half as much current is going into the charging of the battery.

Theory 1 makes good sense but didn't correlate 100% with my observations. #2 does, but means that the problem is a combination of high-current through the *charging circuit built into the E4GT* in the presence of the charging coils (because at a distance from the coils the effect goes away).

This is all observational from one long drive home. I'll do some testing on the bench to see if I can narrow the cause.

One other issue has me puzzled and it's not related to the digitizer but rather to the studs/magnets on the phone that center it on the Touchstone. I have eight charging backs, some old and some unopened. Most are from Pres and one is from a Pixi. I picked a sample of four of them to test out tonight and not one of them has magnets in those four points around the coil.

I pulled a stud out from each and tested it with the lightest ferrous things I could find, including metal filings from sawing on a piece of iron pipe, and got no attraction to either side of the stud. They are marked with a plus or X so it makes sense that they would be polarized, but unlike in your test I'm able to position them on the touchstone and then flip them over and they snap back to the *exact* same place. Also, all of mine were manufactured with the plus towards the *inside* of the phone and I think you said that yours didn't work in that arrangement.

Particularly perplexing to me is the video you linked to of the external touchstone mod. In that example, he definitely has magnets -- they all but jump out of his hand and stick to the phone (which, by the way, I would not have expected to be made of a ferrous metal).

All I can guess is that the design of these studs was changed at some point along the way. Perhaps magnets were used in some models to get a better grip on the Touchstone. Very odd. Not really significant, but odd.

-darren
That doesn't make much sense to me. The device will only draw the current required to Charge and run the phone. Redirecting the current to the rest of the phone shouldn't change the input current since it's being redirected and not reduced. I would even go so far to say that it's drawing more current when loaded down and charging.

It's nearly impossible to get a resistance reading while charging so I'll try and find my Amp-meter and measure what it's actually drawing while charging tonight.


I've been thinking about the metal stubs/magnets and what you've been saying about them. The ones I'm using were from a well used back so it's possible they were magnetized from use.
 

darrenf

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That would probably work great, particularly for the external mod like Honis did. I'm not a case person -- I've never used a case or screen protector. Just a preference thing.

-darren
 

darrenf

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That doesn't make much sense to me.

And you're probably right. After testing some more today, it appears clear that the digitizer weirdness goes away completely when I plug in an audio patch cable to the headphone jack. Since that's how I use the phone in my car, the problem is pretty effectively fixed for me, even though I have no idea what causes the fix. :)

I've been thinking about the metal stubs/magnets and what you've been saying about them. The ones I'm using were from a well used back so it's possible they were magnetized from use.

That's possible. The ones in that video you linked to flipped out of his hand and stuck to the phone strongly enough to hold the induction coil in place (!!), so there might be different types too.

While the internal mod is the most functional design (IMHO :) ), I like the idea of an external slip-on case mod that doesn't void the warranty for users wanting to add easy touchstone charging. I wish the USB cable protrusion was nearly flush when inserted though, and it would also be nice to have USB pass-through to a female port somewhere else on the case. Someone call Quirky... :)

-darren
 

Honis#WP

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While the internal mod is the most functional design (IMHO :) ), I like the idea of an external slip-on case mod that doesn't void the warranty for users wanting to add easy touchstone charging. I wish the USB cable protrusion was nearly flush when inserted though, and it would also be nice to have USB pass-through to a female port somewhere else on the case. Someone call Quirky... :)

-darren

Well, if the mod worked I would have moved on to yours when my warranty ran out. Now I'll just have to wait for the ultimate(ly expensive) charging dock for it.

sad-panda.jpg
 

darrenf

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I identified the fix for the digitizer issue, but I haven't devised a good way to implement it yet. If the ground plane of the phone is grounded to something bigger (your body, a car, etc) the problem goes away. The ground created by the inductive charging circuit is making the phone unhappy.

While I'm looking at ways to handle this, my current favorite requires a mod to the touchstone charging base and I don't really want to go there -- particularly since my phone is hooked to my car stereo most of the time so it's grounded and doesn't exhibit the problem. I think I'll wait to see if the users who are experiencing the same problem from the stock AC charger find an elegant solution.

BTW: I think I scared off some folks with my external charging coil placement, so just for grins I changed that part of the mod and put the coil and studs inside the back. It works pretty well and I confess it does preserve more of the phone's sexiness. I'll update my post in the E4GT Hacks sub-forum shortly.

E4GT-TS-modB1.png
 
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Honis#WP

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I identified the fix for the digitizer issue, but I haven't devised a good way to implement it yet. If the ground plane of the phone is grounded to something bigger (your body, a car, etc) the problem goes away. The ground created by the inductive charging circuit is making the phone unhappy.

While I'm looking at ways to handle this, my current favorite requires a mod to the touchstone charging base and I don't really want to go there -- particularly since my phone is hooked to my car stereo most of the time so it's grounded and doesn't exhibit the problem. I think I'll wait to see if the users who are experiencing the same problem from the stock AC charger find an elegant solution.

BTW: I think I scared off some folks with my external charging coil placement, so just for grins I changed that part of the mod and put the coil and studs inside the back. It works pretty well and I confess it does preserve more of the phone's sexiness. I'll update my post in the E4GT Hacks sub-forum shortly.

Click to view quoted image

I just read your post in the AC Adapter Problem thread.

I still have my stuff setup. Based on your observations I suspect there is noise coming in from the coil causing the issue. I have an oscilloscope laying around I can use. If there is some noise, building a filter should be easy.