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[Nexus 7] Adding internal USB for other devices (HUB,microSD,FM,flash-storage,etc...)

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iAppleDev

Senior Member
Jan 8, 2012
202
100
The project-Adding internal USB for other devices (HUB,micro SD,FM,flash-storage,etc...).

We should have a few deferent options to connect USB internally. This thread should cover them all.

I really want to find a easy solderless method(plug/clips) I have a few ideas but would need to find the female and male connectors for the front camera or maybe soundboard connectors.
or
maybe disconnect the micro USB from the ribbon and run it up to the hub then back to the micro USB connector from the HUB that's one reason for the hub, so we can add a micro SD, a rear camera and the last port (HUB only has 3 ports active, it might be possible to find a different HUB that has 4 ports but this one only had 3) for ether some more flash storage or to hook up the solderless mod to mother board.

We can use the micro USB connection at bottom of the mother board a couple different ways. We could use both the data and power from the connector. We could also just use the data +/- from the micro USB connector and use the power from a different power source like the 7.4V from the battery and drop it down to 5V but none of the wires are 7.4v there is two running at 3.7v, if we could find the 7.4v on the board or a connector somewhere this could be done
 
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iAppleDev

Senior Member
Jan 8, 2012
202
100
Some pics
uploadfromtaptalk1347297809873.jpg

20120902140523.jpg

http://s10.postimage.org/6zg4euc21/N7_cable.jpg
 

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Chrisw_2003

Member
Aug 30, 2012
29
3
Would this guy be similar to the nexus tablet?
nabitablet .com/specs/nabi2
amazon. com/Fuhu-NABI-NABI2-NV7A-7-Inch-Tablet/dp/B008DBI5RI/ref=sr_1_4?ie=UTF8&qid=1342981188&sr=8-4&keywords=nabi+2+tablet
Maybe the board could be close, find out how to use the microSD slot on the nexus 7 tablet?

(sorry about the chopped up url's, I guess I can't post links yet)
 

iAppleDev

Senior Member
Jan 8, 2012
202
100
I Found this little USB HUB and it fits perfect.
This is it before it got striped
18p4s.jpg


Still just in mock up and not connected yet, but it does still close up fine. So I'm pretty sure a hub is a go(for me anyway) and still have room for some flash storage that will go where the rear camera should have gone or just beside the hub:)
 

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jamesst20

Senior Member
Jan 31, 2012
1,672
2,190
25
Wow that's awesome man! Keep on the good work!!

Envoyé depuis mon Nexus 7 avec Tapatalk
 

eBandit078

Member
Sep 5, 2012
40
2
What do you mean by an issue with remounting when you use the power from the USB? I had read somewhere about someone shorting two pins to make the mod work but you could no longer charge and would need a switch to deactivate the short to charge it. If any switch is needed to change anything physically then I was thinking the tiny type that you press with a pen head or similar, that is recessed.

I hope you make progress when your back on it. I ordered the usb otg cable and have some tiny micro sdhc readers that slide into a usb slot that are as thin as a reg. sd card. I figured I could solder wires onto one and mount it for the card reader. I was thinking to use hot glue or similar between the soldered connections for safety since it isnt easy to get factory type solder joints all the time on small stuff (even though I am decent at soldering).

I hope someone can come up with the software hack needed to be able to actually mount the micro sd and install to it like any other tablet can.

Thanks for the pictures and work you are doing, I am sure many are watching :good:
 

Renate

Inactive Recognized Dev / Recognized Contributor
Feb 3, 2012
2,959
1,321
Boston
Nexus 7 (2013)
Moto E5
Just a few comments on this project:

If you put a hub or device in then it requires that you operate the tablet's USB interface in host mode.
Normally, something supplies power and will not accept power for charging when in host mode.
There are hacks to get around this, but I'd see if I could get this all working externally before I started modifying.
You could end up with your hub idea working find, but you are unable to charge the tablet.

When you do lay the cables in, twist the data pair and leave the two power leads straight.
 

bigpetefox

Member
Sep 8, 2010
32
5
Massachusetts
This looks awesome! Can't wait to see the tutorial if one becomes available, these devices get me in trouble! :cool:;):D

Sent from my Nexus 7 using xda app-developers app
 

the0bserver

Member
Sep 5, 2012
19
3
Köln
Have been watching this thread with great interest as well. Indeed, I always only lurked on XDA, this piqued my interest enough to actually join.

Fingers crossed for OP!

Sent from my Nexus 7 using xda app-developers app
 

iAppleDev

Senior Member
Jan 8, 2012
202
100
Hub fits I just need to come up with a 5V power somehow got the Data and ground figured. Can someone come up with any ideas to create 5V power, maybe some fancy circuitry to bump the power from battery to 5V?
 

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eBandit078

Member
Sep 5, 2012
40
2
Hub fits I just need to come up with a 5V power somehow got the Data and ground figured. Can someone come up with any ideas to create 5V power, maybe some fancy circuitry to bump the power from battery to 5V?

What model number hub did you use, does that have the USB OTG built in to it?

I am going to ask a few people in another type of forum about the voltage, a few on there know more than I on this topic. What is the battery stock voltage? I first was thinking resisters but I think we would need to know the exact current going through it to determine the right size. I am searching for tiny DC voltage regulators to see what I can find also, but wasn't sure the stock voltage. Here is some info on DC voltage regulators youtube.com/watch?v=GSzVs7_aW-Y&feature=fvwrel I cant post links yet so it doesn't have the www . The video talks about regulating DC voltage to power 5volt usb devices.

Do you think anyone will have a custom ROM or other hack so we can mount and install to the micro SDHC card once this mod is complete? Because that is what I want before I go this far.

Glad your back at it though! Thanks for your work on this.
 
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Renate

Inactive Recognized Dev / Recognized Contributor
Feb 3, 2012
2,959
1,321
Boston
Nexus 7 (2013)
Moto E5
Normally the 5V power to external devices is fed from a charge pump in the USB PHY interface chipset.
Some non-standard implementations only supply 3.7V battery power.

3.7V may/may not be enough for your hub and SD card.
If you are using 3.7V to a standard USB/SD card adapter, you might try bypassing the LDO in the adapter.

Also, many devices can only host about 100 mA.
Both hubs and USB/SD card adapters can be current hogs.

I think that some actually experimentation is called for before taking a Dremel tool to your tablet.
 
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eBandit078

Member
Sep 5, 2012
40
2
Normally the 5V power to external devices is fed from a charge pump in the USB PHY interface chipset.
Some non-standard implementations only supply 3.7V battery power.

3.7V may/may not be enough for your hub and SD card.
If you are using 3.7V to a standard USB/SD card adapter, you might try bypassing the LDO in the adapter.

Also, many devices can only host about 100 mA.
Both hubs and USB/SD card adapters can be current hogs.

I think that some actually experimentation is called for before taking a Dremel tool to your tablet.

Wouldn't it be best to us a non powered usb hub to split the usb connection? I doubt a small keyboard would use much and as far as I go, I would only use the usb for a small case sized keyboard, charging the device and the micro sdhc card/reader.

So is the battery only 3.7 volts? I was thinking it might be more and we needed to step down, so we need to step it up for the micro sdhc reader?
 

ED2O9

Senior Member
Sep 2, 2009
295
129
So is the battery only 3.7 volts? I was thinking it might be more and we needed to step down, so we need to step it up for the micro sdhc reader?

It's actually two 3.7v Li-Poly cells set up in series for a total of 7.4v. As pointed out (rather rudely) in a prior post, the leads aren't spliced on the pack itself so that a 5v USB input can charge the batteries. My old Acer A100 actually had the batteries spliced so that a 12v charger was needed. It had very weak battery life, but the upside was that the 12V charger would take it from 15% to 100% is a little less than an hour.
 
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littleguy77

Senior Member
Aug 14, 2012
50
28
Virginia
If you put a hub or device in then it requires that you operate the tablet's USB interface in host mode.
Normally, something supplies power and will not accept power for charging when in host mode.
There are hacks to get around this, but I'd see if I could get this all working externally before I started modifying.
You could end up with your hub idea working find, but you are unable to charge the tablet.

Very good points. You may be happy to know that the USB specification recently provided a means for charging an OTG device while in host mode. It's called "Accessory Charger Adapter". See Chapter 6, and in particular Figure 6-2 from the specification:
www.usb.org/developers/devclass_docs/BCv1.2_070312.zip

If you could nail this down, you might solve a bunch of challenges with the +5V supply at once. Not sure what it would take to implement though. A cursory search for dedicated ICs didn't produce anything for me.

When you do lay the cables in, twist the data pair and leave the two power leads straight.

:good: Second that suggestion.
 
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  • 8
    The project-Adding internal USB for other devices (HUB,micro SD,FM,flash-storage,etc...).

    We should have a few deferent options to connect USB internally. This thread should cover them all.

    I really want to find a easy solderless method(plug/clips) I have a few ideas but would need to find the female and male connectors for the front camera or maybe soundboard connectors.
    or
    maybe disconnect the micro USB from the ribbon and run it up to the hub then back to the micro USB connector from the HUB that's one reason for the hub, so we can add a micro SD, a rear camera and the last port (HUB only has 3 ports active, it might be possible to find a different HUB that has 4 ports but this one only had 3) for ether some more flash storage or to hook up the solderless mod to mother board.

    We can use the micro USB connection at bottom of the mother board a couple different ways. We could use both the data and power from the connector. We could also just use the data +/- from the micro USB connector and use the power from a different power source like the 7.4V from the battery and drop it down to 5V but none of the wires are 7.4v there is two running at 3.7v, if we could find the 7.4v on the board or a connector somewhere this could be done
    4
    Camping for a few days with the family, then back at it.
    4
    So I soldered in a switch to id pin and ground pin of micro usb all was good, charged when powered on and switch off, charged when power was off switch on or off. Now I soldered microsd card reader power and data lines to the microUSB connector them ran the ground for card reader up to switch, it works fine for mounting sdcard, but it won't charge when N7 is booted up. It does charge still when not booted up. Maybe I should have ran the ground for the card reader to microUSB port too. But at least it works and is all internal.
    3
    I've been doing a lot of digging into the USB OTG spec, and I think I have a clearer picture now why we might run into problems even if we find some alternative +5V line. I drew up some high-level schematics that show the four operating modes of the stock Nexus, and then shows what happens when you simply tie a peripheral into the usb traces while still permitting external connections through the usb receptacle.

    Basically, if you tie the internal reader to the GND, D+, D-, and VBUS lines behind the receptacle, and short the ID pin to ground, you don't have any problems. You've just replicated the functionality of the OTG cable. The problem arises when you try to attach something to the external receptacle, while the internal reader is still soldered in:

    1. When you plug a high-capacity charger (e.g. the stock charger) into the receptacle, the charger shorts the data lines together. The internal card can no longer be read. Moreover, asserting VBUS from an external source while shorting ID to ground is against USB spec. I'm concerned that the Nexus's onboard USB transciever will go into a safe state that drops all data communication even after the charger is removed. That might explain why some folks needed to reboot their nexus after trying to charge and read at the same time.

    2. When you plug a PC (or any A-device) into the receptacle, the data lines get shared by both the PC and the internal reader. The Nexus tries to be host (A-device) which conflicts with the PC's host status. Not sure if the PC or the nexus can read the card. Not sure if the PC can read the nexus drive. Not sure if the nexus will charge.

    3. When you plug an OTG cable into the receptacle, the nexus acts as host (fine). But the data lines are now shared by both the internal and external peripherals. Not sure if the nexus can read the internal or the external peripherals.