[ED2O9]

try tapping the pogo pins for power

There's no power output from the pogo pins. There's a ground, right and left speaker outputs and a power input.

 

[Kpa2727]

[sub]

There's no power output from the pogo pins. There's a ground, right and left speaker outputs and a power input.

[/sub]
[sub]I was wondering about that, i kept hearing the pogo pins feed stuff but it made no sense to me. Well only thing left as said is a 5 volt source, my guess the speakers feed .5 to 1.5 volts so thier out, the screen might take 5 volts to run. I don't get it though. if you tapped say the pogo pin ground and kept the 5 volt source from the usb ribbon cable connector then the ground would remain constant and not chage. my understanding of OTG and charging is the ground switches due to charging mode from a ground to a neutral. that then turns off otg but enables charge. by keeping a different ground, that should fix the issue.[/sub]

 

[ED2O9]

I don't know the specifics of how the port switches from OTG to charging, but I do know that the SD card works perfectly until I plug in a power cord, then it disables the reader and still doesn't charge. Even after I remove the cable, I still can't get the card to mount unless I reboot the tablet. I read that adding a resistor to one of the grounds will enable charging, but it will still cut off the OTG setup. Connecting the reader to an alternate power source is the best solution, provided that I can find one.

 

[ED2O9]

[sub]if you tapped say the pogo pin ground and kept the 5 volt source from the usb ribbon cable connector then the ground would remain constant and not chage.[/sub]

I get what you're saying and can give it a try tomorrow. It's pretty late here.

 

[Kpa2727]

It's 2 am i have to work at 8 am i just wrapped up a 10 hour day without a lunch or break. i feel the pain.

 

[r4ptor]

Ok, so that i'm getting this right.

the only problem is to get a 5V connector on the Nexus 7? With this connectionpoint it should be possible to solder a micro sd card reader to the micro usb port(and solder the pin 4 of the micro usb port to ground to get usb on the go)?

 

[iAppleDev]

Yes that is right. I need some one to scope the board for other possible data+/- lines and 5+/- or I'm stuck using the MicroUSB lines.

 

[r4ptor]

Ok, so why don't grep the 5V over the battery and get it down to 5V with a voltage divider?

 

[Kpa2727]

couple of reasons, its a constant draw on the battery and finding a reguator that small can't be a easy task. I got worf, i have to have surgery next wed, i probably will be away for 2 weeks or so from this thread. good luck guys.

 

[iAppleDev]

couple of reasons, its a constant draw on the battery and finding a reguator that small can't be a easy task. I got worf, i have to have surgery next wed, i probably will be away for 2 weeks or so from this thread. good luck guys.

Worf sorry to hear that. I wish you luck

 

[r4ptor]

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

 

[Kpa2727]

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".

 

[nst6563]

Does anyone know what switch the Nexus7 uses for the usb? For example, http://www.ti.com/lit/ds/scds325/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.

 

[maaneeack]

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

 

[nst6563]

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.

 

[Kpa2727]

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.

 

[nst6563]

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.

 

[ED2O9]

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.

 

[ED2O9]

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.

 

[nst6563]

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.