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  1. #101  
    Thanks to Wilywyrm for the info on the innards of the TP Barrel PSU. Here is some information on the MicroUSB Charging Specification that I gleaned from USB - Wikipedia, the free encyclopedia

    In Battery Charging Specification,[40] new powering modes are added to the USB specification. A host or hub Charging Downstream Port can supply a maximum of 1.5 A when communicating at low-bandwidth or full-bandwidth, a maximum of 900 mA when communicating at high-bandwidth, and as much current as the connector will safely handle when no communication is taking place; USB 2.0 standard-A connectors are rated at 1.5 A by default. A Dedicated Charging Port can supply a maximum of 1.8 A of current at 5.25 V. A portable device can draw up to 1.8 A from a Dedicated Charging Port. The Dedicated Charging Port shorts the D+ and D- pins with a resistance of at most 200 Ω. The short disables data transfer, but allows devices to detect the Dedicated Charging Port and allows very simple, high current chargers to be manufactured. The increased current (faster, 9 W charging) happens if both the host/hub and devices implement the new charging specification.

    This suggests that the "Standard" Spec only requires the D+ & D- terminals to be bridged at the PSU Socket. I haven't tested this yet but I suspect that the voltage divider is there to hold the pins at a nominal 2.5V though this may be sensed by the TouchPad when initiating the Charging sequence.

    I have checked the mant USB Power adapters that I have bought and the only one that has the D+ & D- Terminals bridged is this one eBay - The UK's Online Marketplace
    It is the only device I have that correctly charges my Nokia N900 which has the same charging spec. I will list the devices that I know NOT to have the D+ & D- pins bridged on the 2.1A outlet:

    Dual 2 Port USB Car Charger Power Adapter For ipad iPod iPhone 4G Black | eBay

    Car Cigarette Powered Dual USB Adapter Charger For iPhone iPod iPad Cell Phone | eBay

    EU USB Power adapter Wall Charger 4 iPad iPhone 4G iPod | eBay

    10W USB Power Adapter AC Charger for iPad 2 iPhone 4 4G Output 5.1V 2.1A US PLUG | eBay

    Just for clarity, the above four chargers do NOT work.

    I will test the White one that charges my Nokia N900 and has the D+ & D- pins bridged tomorrow. It is 03:00 in the early hours of the morning and the Formula 1 Korean GP free practice has just started!
  2. #102  
    OK if I get this straight, by taking any 2 amp rated USB car charger and moding it similar to the diagram wilywyrm posted above we should have a functional charger for the TP.

    That seems easy enough...

    If that's not the case what am I missing?

    (I have ordered and tried a few USB car chargers rated at 2.1 Amps and would be willing to modify one of them for a try as to chip in for the team of PSU dissambler and car charger testers...)
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  3. #103  
    Quote Originally Posted by RICKV View Post
    OK if I get this straight, by taking any 2 amp rated USB car charger and moding it similar to the diagram wilywyrm posted above we should have a functional charger for the TP.

    That seems easy enough...

    If that's not the case what am I missing?

    (I have ordered and tried a few USB car chargers rated at 2.1 Amps and would be willing to modify one of them for a try as to chip in for the team of PSU dissambler and car charger testers...)
    RICKV, you're spot on. I've already used this same circuit with a computer and 2 generic sub-2A chargers, with no trouble getting the lightning icon. Happy modding!
  4. #104  
    OK Guys, this may save you some time and hacking

    I have tested the Car PSU I recommended earlier and can verify that it works perfectly.

    I also checked and can verify that it DOES have the D+ & D- terminals bridged AND that there appears to be a voltage divider reading 8.6K to V+ and 7.7K to V-. Though lower impedance, it gives the same voltage on the Data pins.

    Update: On further measurement, this charger was not charging at full current. The TouchPad was fully charged when I made this observation. See posts later in this thread for the conclusions reacged together with WilyWyrm and Rickv.

    I checked all of the others and they don't.

    If any of you are considering hacking a PSU, it may be easier to add the Bridge and potential divider externally by splitting one of these and adding the circuit in it. eBay - The UK's Online Marketplace
    Last edited by Wheel_nut; 10/19/2011 at 05:46 PM. Reason: Updated findings on charging current.
  5. #105  
    also seller on US ebay site - $2.99 shipped, also from Shanghai
    Dual 2 Port USB Car Charger for iPad iPhone 4G iPod 2A | eBay

    There are some about 10cents less with the same specifications printed, but the adapter housing differs in their photos.
  6. #106  
    Quote Originally Posted by tweak42 View Post
    2.1A is what the iPad is speced for thus many of the manufactures use that as a baseline. Unfortunately there seems to be something proprietary or at least different in the way iPad & Touchpads identify the max output of an adapter. It looks like the only guaranteed way to charge at 2.0A is use an AC inverter.
    They do some counterintuitive things, here's a really good read and circuit diagrams http://www.ladyada.net/make/mintyboost/icharge.html
  7. #107  
    I'm certainly no electrical engineer, but here I have done the autopsy of a Griffin P2275 which can be bought for less than 2$ with free shipping on ebay.

    I'm a little perplexed as of what I found after dismantling the unit.

    I have drawn red lines to enhance the circuit pathways so it would be clear for everyone.
    In the image below is the backside of the 2.1amp USB connector. On the opposite side of the PCB is a bridge between the 2 data pins. On the front are already 2 sets of resistor which from reading a bit on the internet would show as the following: (absolutely not sure of those value, please confirm or correct me I will adjust the post to show proper values)
    513 : pull down 5.1300 ohms x2
    473 : Pull up 4.7300 ohms
    753 : Pull down 7.5300 ohms

    Since we seem to a bridge and resistors as stated in other posts, what makes it not functional?

    I guess the value of the resistor make it so the voltage sent through the data lines is not consistent with what is expected, hence the high power charging cycle is not initiated.

    I have found the resistors mentioned above in local store for 25 cents for 5 unit of each value... talk about a cheap mod. Do you think that if I remove the surface mount already soldered on the adapter and replace them with the proper ones it will correct the voltage and make it work?

    Sorry I need some handholding here, as I am not that knowledged in electronics.

    (October 16th, added Images and images description)
    Added Images without annotations
    img_0156.jpg show the front of the board. My annotations and markings enhance the path on the circuit board for clarity.
    P2275_circuit_front.jpg showing the circuit pathways without the annotations
    P2275_circuit_back.jpg showing the other side of the PCB wit the bridge pathway between the 2 data pins. (Sorry I cannot have a clear sight to the actual connections being very close to the connector housing, even though I'm fair at MACRO photography I can't this one because od my material's limitation...)
    Attached Images Attached Images
    Last edited by RICKV; 10/16/2011 at 10:59 AM.
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  8. #108  
    I got the Champtek CC-210 5V 2.1A plug from Fry's - it gives the low power nag, but does slowly charge the device. It looks to be about the same as a 1A charger. That's too bad, because the small profile is really nice.

    I've ordered the eBay charger that Wheel_nut mentioned. If anyone else gets that one and can confirm it's working, please post it. Thanks for checking that out, Wheel_nut!
    Last edited by bdbr; 10/15/2011 at 08:27 PM.
  9. #109  
    Quote Originally Posted by RICKV View Post
    I have drawn red lines to enhance the circuit pathways so it would be clear for everyone.
    In the image below is the backside of the 2.1amp USB connector. On the opposite side of the PCB is a bridge between the 2 data pins. On the front are already 2 sets of resistor which from reading a bit on the internet would show as the following: (absolutely not sure of those value, please confirm or correct me I will adjust the post to show proper values)
    513 : pull down 5.1300 ohms x2
    473 : Pull up 4.7300 ohms
    753 : Pull down 7.5300 ohms
    513 : pull down 5.1300 ohms x2 51K-Ohms (51 and 3 zeros)
    473 : Pull up 4.7300 ohms 47K-Ohms
    753 : Pull down 7.5300 ohms 75K-Ohms

    Are you saying that there are two 51Kresistors in parallel on the pull-up?.... and a 47K in parallel with a 75K on the pull-down?

    Are you absolutely sure???
    Since we seem to a bridge and resistors as stated in other posts, what makes it not functional?

    I guess the value of the resistor make it so the voltage sent through the data lines is not consistent with what is expected, hence the high power charging cycle is not initiated.

    I have found the resistors mentioned above in local store for 25 cents for 5 unit of each value... talk about a cheap mod. Do you think that if I remove the surface mount already soldered on the adapter and replace them with the proper ones it will correct the voltage and make it work?

    Sorry I need some handholding here, as I am not that knowledged in electronics.
    Not sure of what you are trying to do here....
  10. #110  
    Quote Originally Posted by Wheel_nut View Post
    513 : pull down 5.1300 ohms x2 51K-Ohms (51 and 3 zeros)
    473 : Pull up 4.7300 ohms 47K-Ohms
    753 : Pull down 7.5300 ohms 75K-Ohms

    Are you saying that there are two 51Kresistors in parallel on the pull-up?.... and a 47K in parallel with a 75K on the pull-down?

    Are you absolutely sure???
    You can look for yourself on the picture it is very clear what is soldered on the circuit board.

    Quote Originally Posted by Wheel_nut View Post
    Not sure of what you are trying to do here....
    Not trying to do anything, just stating that if according to wilywyrm, if a bridge and resistor are used in a USB PSU setup the TP should recognize the power. However even though there seems to be an appropriate circuitry here it does not work. Just wandering if it is due to improper value of the resistor installed and if I remove them and use other value resistor will it work.

    The resistors are on the front of the circuit board from my photography perspective and on the other side of the PCB is a bridge connection between the 2 data pins.

    The other thing I am wondering about is the following: If you look at the picture I took, on the right side the top 47k ohms resistor is properly aligned, as the 75k ohms below is upside down,maybe suggesting a reverse polarity or something else.
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  11. #111  
    Here is another unit on the altar. I don't have a visual clue on this one as to if the 2 data pins are bridged or not, as I can't see the other side of the PCB.

    On this side the 2 data pins are clearly not connected to one another. This unit is a single USB 2.1amps rated PSU.

    Comments anyone?
    Attached Images Attached Images
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  12. #112  
    Rickv, What I cannot see in pic1 is the printed circuit track connecting the resistors to the USB connector pins. ... and no, resistors have no polarity.

    You need to check with a multimeter for continuity, and check "both ways" in case there is a semiconductor contributing to the reading value. Also, scrape away the screen printing to expose the copper track.

    The voltage sent back to the TouchPad on the Data pins DOES set the current that the TouchPad will draw. Note that this is NOT the case with the Apple products where I believe that the charge current is determined by a mechanism in the cable or Device.

    Lastly, despite the rating printed, it wouldn't surprise me if the PSU was incapable of supplying 2.1A
  13. #113  
    Newer Apple chargers for phones/pads provide 2.8v on D- and 2.0v on D+ this low level signaling state tells the device to draw as much power as it can. Like I said in my previous post this page does a great job on how apple charging works with the USB spec.
  14. #114  
    last night I just used my phone car charger to charge it, it took a few hours but it charged. Also you must have the screen off and not be using it, for emergencies its nice to know it still charges withthe old chargers just in case you forgot the touchpad charger like I did last night.
  15. #115  
    Don't get me wrong here, any of those chargers will charge the TP... very slowly!
    As mentionned in other posts in this thread, what we are looking for for is enabling the TP to recognize the 2+ amps and charge at max capacity over the shortest period, enabling full use while charging, not just barely keeping charge or reducing the discharge process.

    For that to happen, we need to have the lighting on the battery indicator to appear, and this means adjusting the circuit pathway with proper values to enable this.

    Wheel_nut I have uploaded more images above and added image descriptions hope this helps you figure it out.
    Last edited by RICKV; 10/16/2011 at 11:00 AM.
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  16. #116  
    Yes, the resistor values matter, but I have to agree that the parallel pairs of resistors is strange. Rick, the first charger you disassembled had the necessary circuitry, it's just that the values of the resistors affect the voltage on the power lines. So by substituting the appropriate values, you can make the charger work with the touchpad. But only replace one set (horizontal pair, parallel to USB port pins). Completely remove the other pair.
    They might have been put there to make the charger compatible with another device, but soldering in 2 pairs of resistors will change the total resistance on the lines and may make the charger unrecognizable by the touchpad.
    And don't worry about the orientation of the resistors, as Wheel_nut said, they are nonpolar.

    As for the second, you can bridge the data lines yourself by plopping down a nice blob of solder on the middle two pins. Again, pick a set and replace with correct values. The other set is unnecessary to us.

    Also, Wheel_nut, thanks for sharing the news about your car charger! It's great to know that it's not absolutely necessary to tear apart our chargers.This does open the floodgates for legions of people asking "does this one work?", though. :P
    Last edited by wilywyrm; 10/16/2011 at 12:52 PM.
  17. #117  
    That is awesome, now i know what I have to do.

    Thank you very much to wilywyrm and wheel_nut for their insight and handholding.

    I should do the mod later tonight and will keep you posted on my success or failure... I'm good at soldering, however replacing SMT resistors with regular ones may be tricky.
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  18. #118  
    RICKV, I have just opened up a Hong Kong "Apple" iPad Mains Charger and I think I have the answer to the seemingly illogical Resistor configuration:

    The Apple charger requires 2.0V on the D- and 2.7V on the D+ lines to charge at high rate.

    If you look at your charger, you will see that the upper Voltage divider is connected to the third Pin from LHS i.e. D+ and 5.25V*51/94=2.8V.... and the lower Voltage divider is connected to the second Pin from LHS i.e. D- and 5.25V*51/126=2.1V.

    So, the Charger is designed for the Apple standard and then adapted to the "generic" standard by bridging the D+&D- Pins on the back of the PCB.

    Edit: I have just bridged the D+ & D- lines on the "Apple" Charger and it is now charging my Nokia N900 BUT NOT the TouchPad. When plugged into the TouchPad, it gives the Low Power Warning ..... BUT WORSE, the Touchscreen becomes erratic. I think I need to remove the existing resistors and replace with the 240k Pull-up and 300K Pull-down as per Wilywrm's findings.

    This suggests that your charger should charge the TouchPad at fiull pelt! Does it?
    Last edited by Wheel_nut; 11/02/2011 at 10:24 AM. Reason: Update: Not charging TouchPad
  19. #119  
    Initial results are not that great... here is why, I have used both adapters already shown and after seeing wheel_nut's post, I have bridged D+ and D- without success on both devices.

    Then I took adapter #1 and moded it with the 2 resistors. Now the TP lightning comes on, however I must have broken another circuit pathway as I don't get any current...

    even though it is connected, consumption remains at around -700 mA, which is the drain I get before plugin in... I'll look at my solders tomorrow, maybe in the process I have affected something else as the work area is very tiny.

    I will also try modding the other adapter. maybe I'll have more luck with this other one, as the SMTs are more accessible because of the design of the adapter

    Stay tuned for take 2 tomorrow.
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  20. #120  
    I think I may have part of the issue...

    In my first mod, I have removed all 4 resistors to replace them with a 250k and a 300k.

    However looking closer at the pics I took yesterday, tell me if you see the same, but the top pair of resistor are linked to the D+ circuit. At this point I have also linked the D+ and D- without success.



    Look carefully at the lower pair of resistors... the circuit pathway does not seem similar. There does not seem to be a link to the D+...

    Maybe I need to only remove the top one and replace with the 240/300. Removing the lower pair may have broken the actual charging pathway, explaining why I don't have any current anymore even though now the lightning appears...

    I'll try and scratch the white markings to have a better look at the circuit pathway.

    Comments?
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