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I noticed that besides the spot above the headphone jack, the other nearly perfect spot for say a small 64GB thumb drive would be in the empty housing of the rear camera. I have a sandisk 16gb drive that would fit right in there if a half a mm was shaved off the sides of the pcb on the flash drive (which there's plenty of space for that small amount).

Also - to get power from the pogo pins...maybe it needs to be tapped before the diode. If I'm not mistaken those pins should be protected via diodes to prevent 'wrong way traffic'.

I'd be concerned about charging and having it mounted at the same time. example would be transferring from pc to the tablet via usb cable. If I understand correctly, this would unmount the usb and go into data xfer/charge mode.

There are some datasheets for usb controllers out there that list the impedences for the ID line in the micro-usb spec, maybe one of those is the key to having both charging AND mounted at the same time. I believe 36k is the resistance needed...but would need more confirmation and I need another flash drive and some connectors to find out.
 

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I did crack it open and unfortunately my eyes aren't what they used to be and I don't have a magnifying glass to read what's on the smaller smt chips. I have no problems soldering on a level that small. The 36k resistors were smt and weren't much hassle, most people just need practice.
 

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What value resistance? I have some SMT resistors to borrow from and those will fit better than the standard size. Depending on what the value is if I have it or not. I tried 36k with no success, but I didn't solder to the inside of the nexus, I soldered to the otg cable I made.
 

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I see you've got connections going to the card reader and the hub, and possibly to the usb port on the nexus. Do things work this way? Does it charge and use the reader at the same time?

:EDIT: took a closer look and it looks like the other set of wires aren't connected.
 

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can you just solder "extension" wires to the onboard connectors? This way you wouldn't be working directly with the onboard circuitry, but rather the extension wires that are attached. Sort of like testing an existing circuit with an external breadboard.

:edit: Couldn't the 'common ground' be gotten at it's source on the battery? There are 2 black leads from the battery, which both connect to a copper trace that seems to go around the board. Upon looking closer, there looks like some spots for filter caps from the other leads from the battery to the ground. I don't think finding the ground would be the issue, but rather the 5v or +/- data points.
 

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I saw that post and have yet to fully read it. There are plenty of ground points on the board according to some tests I was able to do with a meter today. I was also able to identify the data +/- points away from the fragile ribbon connector. I soldered wires to them in prep for mounting a new drive internally. I also tapped the power and ground from the smt ribbon cable. I tucked away the wires for later use, I'll post some pictures in a while after I'm done making some notations on them.

Good luck with the surgery.

:EDIT:

Pardon the images if they're very clear ....I took them with my SGS3 since our camera is full of sand from the beach (thanks kids!).


By nst6563 at 2012-09-02


By nst6563 at 2012-09-02


By nst6563 at 2012-09-02
 

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The reds are 3.7, the others are 1.7. I haven't dismantled mine to get to the front either, and most likely won't until I have enough funds to replace something should I break it.

Here are a few good reads on USB OTG and charging specs. It almost seems like it's fairly specific to the usb controller the tablet uses. The one thing being in common is the resistance on the ID line to activate certain functions.

http://www.ti.com.cn...001/sszy001.pdf

The host (A-device) would be the Nexus7, the peripheral (B-device) would obviously be the drive. That link to the TI document lists that the controller itself boosts the voltage to the B-device when it's entered as the peripheral.

According to WIKI:
"
OTG Micro Plugs

With the introduction of the USB Micro Plug, a new plug receptacle called Micro-AB was also introduced. It can accept either a Micro-A plug or a Micro-B plug. Micro-A Adapters allow for connection to Standard-A plug type USB cables, as used on standard USB 2.0 Devices. An OTG product must have a single Micro-AB receptacle and no other USB receptacles.[sup][4][/sup][sup][5][/sup]
The OTG cable has a micro-A plug on one side, and a micro-B plug on the other (it cannot have two plugs of the same type). OTG adds a fifth pin to the standard USB connector, called the ID-pin; the micro-A plug has the ID pin grounded, while the ID in the micro-B plug is floating. The device that has a micro-A plugged in becomes an OTG A-device, and the one that has micro-B plugged becomes a B-device. The type of the plug inserted is detected by the state of the pin ID .
Three additional ID pin states are defined[sup][4][/sup] at the nominal resistance values of 124 kΩ, 68 kΩ, and 36.5 kΩ, with respect to the ground pin. These permit the device to work with a USB Accessory Charger Adapter which allows the OTG device to be attached to both a charger and another device simultaneously.[sup][6][/sup] These three states are used in the cases of:
  • A charger and either no device or an A-device that is not asserting VBUS (not providing power) are attached. The OTG device is allowed to charge and initiate SRP but not connect.[sup][6][/sup]
  • A charger and an A-device that is asserting VBUS (is providing power) are attached. The OTG device is allowed to charge and connect but not initiate SRP.[sup][6][/sup]
  • A charger and a B-device are attached. The OTG device is allowed to charge and enter host mode.[sup][6][/sup]
USB 3.0 introduced a backwards compatible, SuperSpeed extension of the Micro-AB receptacle and Micro-A and Micro-B plugs. These contain all of the pins in the USB 2.0 Micro and use the ID pin to identify the A-device and B-device roles. Additionally they contain the additional SuperSpeed pins."
http://en.wikipedia....i/USB_On-The-Go
Here it lists a "standard" impedance specification, however it seems that not all controllers must adhere to the standards and according to another document which I can't for the life of me find right now there were a number of impedance ranges for use on the ID line.

There's also good info in this article http://www.maxim-ic....dex.mvp/id/1822 which also mentions the usage of HNP or SRP which could simply be a kernel patch to allow such a device to charge via setting the HNP.

To get 5v it may have to be coming from a separate circuit with the source from the battery leads to 'sum' the voltage output of the battery to get 5v. With small SMT componets I wouldn't see a problem fitting something similar to that to where iAppleDev has a usb hub placed

I honestly think the answer is in software at this point to activate the charge function. For hardware source of 5v I think a simple op-amp based summing circuit would be the best option if one isn't found on the board itself.
 

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To get the 5v, it's possible to simply sum the two power inputs from the battery (3.7 and 1.x) with a zener and a resistor. OR - get fancy and use an op-amp circuit to give the 3.7v line a small boost. I'll see if I can mess with something this week for adding the two voltages via tiny circuitry. It's been a while since I took those EE classes so I'm certain I'll end up toasting a resistor or two :)

Wonder how the surgery went? Hope all turned out well.
 

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I think just a micro-sd reader might be able to, but not a usb hub since it has to pass the voltage and current on to the slave devices. I could be wrong though.

I didn't get a chance to throw together a simple circuit to add voltages this evening, up to my eyes in work. Hopefully this week I can or someone else can hop in the bandwagon and beat me to it.
 

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Exactly what Mentose457 said. Not to mention that the otg cable interface 'hanging' from the tablet will eventually stress the micro-sd connector enough to slightly distort it and cause the connection to fit loosely.

There are a couple threads over on xda with the same pursuit. Check them all out, all are good work towards a possible solution. There was even someone on xda that was able to use the external otg as the primary sdcard yielding 64gb of space.

Still a long way to go yet though. I wish I had my tablet here, I could do some more testing on it. Unfortunately it's traveling with my son for the next week.
 

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hopefully he didn't take your n7 into the sandbox like your poor camera lol :)
Got my n7 back....no sand! He didn't get to take it to the beach though like the camera :)
Not sure if I'll have any time to mess with those data points and the voltage points since we're moving here in 10 days. Moving is always hell.
I've got the inside pre-wired though, so if I get the chance it shouldn't take long.

Problem with tapping into the 3.7v from the battery is that the flash drive would be using power even when the tablet is off.
 

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I think that the most important piece we're all missing (besides schematics of course) is the fact that it's unknown whether or not the n7 will respond to impedance on the ID pin. Standard USB specs allow for varying impedance on the ID line, and it's up to the device to detect and enable/disable features based on the value of that impedance.

I'm not a kernel dev either, but there should be a way to check for those impedance values. Roms like ParanoidAndroid have native support for OTG drives while the stock based roms require stickmount or other similar software. Maybe it's more than just a kernel hack to enable functions - who knows. Looooong way to go.

There's a thread on xda where a link to a micro-sd slot was linked to on Mouser which had a switch integrated into it. That would be ideal for use in this situation to trip the ID line to ground when the micro-sd is inserted.

btw - I tried the micro-usb to HDMI mhl adapter from the sgs2 and it doesn't work for the nexus
Maybe that's a kernel patch too? I cracked it open to look inside but didn't have the time to poke around and do tracing. Now it's packed in a box until after I move.
 

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Yes, this is another important question. In my searching, I have not yet found the answer. It will all depend on the capabilities of the chips on the nexus motherboard, whether or not they can measure the impedance on the ID pin. If they can't measure the impedance, then there's not a whole lot the software can do. Here's a really good explanation here from another thread:

My hunch is that, since the OTG+charge spec (ACA) was only ratified in December 2011 (and updated in March 2012), there were no ASICs in production yet with this capability at the time the Nexus motherboard design was finalized, and hence the Nexus 7 is a "category 3" device as discussed in the link.

On the other hand, you could just fake it and patch the kernel to think it's attached to one impedance or another. Then you'd just have to be sure the software state was always in sync with the actual hardware configuration.

I may be wrong, but I think effectively all they're doing is baking the stickmount app into the kernel.
very well could be baked into the kernel or the rom itself. It does mount in a different location - but then again TWRP can use the OTG drive natively as well. I'm not a developer so I have no clue


Possible the newer revisions of the N7 will have a ratified chip in them. One can only hope.
 

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http://dl.dropbox.com/u/47767898/me370t.pdf

Let me know if the link doesn't work.
Hopefully someone that can read schematics better than I can make sense of the section Titled "T30 USB, HSIC, ICUSB"

Looks like there is a function defined by a 100k resistor to ground on the ID line. Below that, there are also specifications for an eMMC device.
 
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