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[Open Discussion] Soldering in Micro sd card reader to Nexus 7/ build log

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r4ptor

r4ptor

Average Android

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Posted 28 August 2012 - 09:48 PM #51

Oh crap, sorry to hear that. Good luck and get well
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OP Kpa2727

Kpa2727

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Posted 29 August 2012 - 09:55 AM #52

thanks guys, i'll still check in till around tues or so surgery is on wed.

i almost forgot, as for the tiny card readers i got mine on ebay for around 2-4 bucks. look up "micro sd card reader mini".

Edited by Kpa2727, 29 August 2012 - 09:57 AM.

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nst6563

nst6563

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Posted 29 August 2012 - 10:41 AM #53

Does anyone know what switch the Nexus7 uses for the usb? For example, http://www.ti.com/li...325/scds325.pdf is a TI chip that also displays the impedence values for the ID line on the micro-usb port. One of these impedence values may be the key to getting the memory card reader to work at the same time that the device is charging.
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maaneeack

maaneeack

Average Android

Posted 29 August 2012 - 02:49 PM #54

Couldn't you tap the wifi/bluetooth/gps or camera to get the power?
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nst6563

nst6563

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Posted 30 August 2012 - 05:13 AM #55

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.

Edited by nst6563, 30 August 2012 - 05:14 AM.

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OP Kpa2727

Kpa2727

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Posted 30 August 2012 - 11:30 PM #56

something intresting i noticed was that the samsung tab 7 inch is a spitting image of the nexus 7, same form factor, same buton layout, same beveled edges, the samsung has a camera and a IR blaster. it's 250.00 with a dock. not a bad deal.one was returned at work the other day so i glanced over it. now onto the point. I can almost hinge bets they use the same board with different plugs. the golden ticket is probably in the FCC records disclosed of the devices. probably if you pull thos schematics, youll have most of the answers.to all the comments about before diodes, i highly suggest you pop the cover or research some pictures. damn near half of the N7 is surface mount stuff. you need a damn needle to solder onto that stuff. with public tools you wouldn't be able to do much, with commercial technology you'll sink 2 times the value of the tablet into it just for a sd card slot. i encourage development but practicality guys. were looking for a simple connection that's feesable for everyone with solder skills to do. I'd say nail down a solid source to enable usb first, then work out host and charge functionality. lets be honest, you'll never need to charge and watch movies more then the life on the tab. it kills me when i read about it, you should easily be able to get through 2 movies before needing a charge.so whats the hassel in adding all these other road blocks? lastly Hdmi out isn't even capable if yet or ever will be. so why worry about a charge right now and host? one more thing if you need storage and charge so bad, just move the file with Root Explorer to internal temporarly.

Edited by Kpa2727, 30 August 2012 - 11:33 PM.

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nst6563

nst6563

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Posted 31 August 2012 - 03:29 AM #57

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.

Edited by nst6563, 31 August 2012 - 04:35 AM.

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ED2O9

ED2O9

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Posted 31 August 2012 - 09:25 AM #58

I actually bought a Samsung Tab 2 7.0 at the same time a the Nexus 7, and the performance of the Samsung was so far below the Asus it wasn't even a fair battle. Also, the developer base for the Nexus 7 is soooo much better than any other tablet I've owned. Throw in the terrible Samsung device support, and it was a vert easy decision.
Anyhow... in regards to the boards, I highly doubt that they use the same boards. Samsung and Asus are rivals and wouldn't share proprietary components like circuit boards. Aside from both being Korean, I think the similarities end once you open the cases. I might be wrong, so it's worth looking at an Galaxy Tab tear-down.
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ED2O9

ED2O9

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Posted 31 August 2012 - 09:34 AM #59

BTW - No luck on using the pogo ground. I've been up to my eyeballs in work, but this weekend I plan to spend some time on this project. I picked up a new variable wattage soldering iron and some resistors. I'm going to try to use everything from the micro USB port, but add a resistor to the back side of the neutral lead to allow charging. Several people have had success with this set-up... using external splitters. Doing it internally is going to be tricky, considering that I have to splice into the lead right behind the port and there's no room. I'll probably have to trim away some of the plastic speaker housing, but it should work. Keep your fingers crossed. :P
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nst6563

nst6563

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Posted 31 August 2012 - 10:29 AM #60

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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