Modification: Charge via USB

[ZapWizard]

Hello all, I am a new 770 user thanks to Woot.
I am also a computer modifier, and like to fix annoying design features in products. In this case it is hauling a 5volt wall wart around to charge my 770, when there is perfectly usable 5volt power on the USB connector.

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This modification will make it so that your Nokia 770 can charge off of a USB port, rather then hauling around the wall-adapter. All you need is any normal mini-USB cable.

What makes this possible is that the wall-adapter puts out 5volts, which is the same voltage on a USB port.

This modification is a DO AT YOUR OWN RISK modification. It will certainly void your warranty. I am not responsible for any damage to your device by following this guide.

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First remove the battery, cover, and memory card.
Then remove the five torx screws on the back of the 770.
Two of them are located under plastic caps at the top.

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Using a plastic prying tool (iPod repair websites sell them) remove the bottom plastic plate that covers the I/O jacks
(I actually used a small screw driver as I can live with small marks in the plastic)

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Remove the faceplate.
The LCD may stick to the faceplate, but it is not glued in place, it will come undone with a small amount of pressure.

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Carefully fold the LCD over to expose the PCB.
There are several tabs at the left hand side, and around the battery housing that you have to release to get the back-plate off.

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Flip over the PCB, make sure to pad the LCD.

It is amazing that Nokia can cram so much technology onto such a small space, and with so few parts.

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Note the location of the USB connector.
To the right of it is two small gold pads, this mate to the charging connector.
The right most pad is +5volts.
On the USB connector +5volts is on the left most pin.

I used a multimeter to determine that +5volts-charge is connected to a surface mount ferrite. It is a small gray component. This is where I will run my USB voltage to.

(I don't recommend soldering directly onto the gold pad, as then your normal charge connector won't mate with the PCB)

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I soldered a wire from Pin 1 on the USB connector to one side of the ferrite.

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Carefully put everything back together.

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Power-up before plugging in the USB connector.
Then plug-in the USB connector.
Depending on how your computer manages USB power, it may turn the port off if it doesn't mount the 770, but I find with a memory card installed it stays on.

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That is it, now you don't have to haul around that dang wall charger.
Just find any mini-usb cable and your ready to go.

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Sorry folks, I don't do these mods for others, so don't ask.

/Edited to spelling, and errors

[fpp]

Very nice Howto, thanks for the effort !

For tinkerers who don't have the guts to disassemble their tablet, or don't "do" precision soldering, perhaps a modified USB cable with a tip that goes into the charger connector would be a simpler approach, with almost the same result ?...

[robbh66]

Haha...for 2 reasons...

One: I was looking around yesterday and wondering why nobody had done this before as it seemed pretty obvious.

Two: I saw those pictures on flikr earlier here: http://nokia770.com/ but didn't know for sure this is what it was and where the full writeup was.

Very nice job indeed. How difficult would this be for the somewhat-beginner? I know how (well in theory at least) to solder and have soldered stuff before but it never looks _that_ pretty.

To those of you who have been around a nokia 770 for a while- is there a downside to this? I figured Nokia HAD to have a good reason not to have just done this from the getgo? The only one i could think of was in case people plugged in two power sources at the same time but they could have easily fixed that by just using a USB for data and charger instead of what it has now.

edit: Oooh I just had an idea. I've seen a lot of talk about people having to use powered hubs to get usb devices to work. Would it be possible to send power from the power connector leads to the USB port to send power to USB connected devices? I'm guessing you couldn't do both mods at once, huh?

[robbh66]

Very nice Howto, thanks for the effort !

For tinkerers who don't have the guts to disassemble their tablet, or don't "do" precision soldering, perhaps a modified USB cable with a tip that goes into the charger connector would be a simpler approach, with almost the same result ?...

Seems to me that would be the exact same power result- but you're still locked into carrying that cable around too. Reminds me of my palm's charger tip- have a thing that fits on any sprint car charger BUT i still have to carry the damn thing with me.

[ZapWizard]

perhaps a modified USB cable with a tip that goes into the charger connector would be a simpler approach, with almost the same result ?...
Yes, that would work, but that is a custom cable to lose, if you do it internally then you can get a cable at any store if you forgot yours at home.
Heck I had neither the wall-wart, nor a mini USB cable with me when I started the mod at work, but asking around a few cubes and I was able to find one to borrow in minutes.

It is not difficult to do, but you just have to take care not to bridge any connections with solder, or break anything when opening it up or putting it back together. The reason mine is so clean is that I had the right wire, a expensive soldering iron, tiny tip, and stereo microscope to do it with. (Work)

Very nice job indeed. How difficult would this be for the somewhat-beginner? I know how (well in theory at least) to solder and have soldered stuff before but it never looks _that_ pretty.

To those of you who have been around a nokia 770 for a while- is there a downside to this? I figured Nokia HAD to have a good reason not to have just done this from the getgo?

edit: Oooh I just had an idea. I've seen a lot of talk about people having to use powered hubs to get usb devices to work. Would it be possible to send power from the power connector leads to the USB port to send power to USB connected devices? I'm guessing you couldn't do both mods at once, huh?

The reason Nokia probably didn't do this from the beginning is because technically the charger is rated at 900mA of output, and a USB port isn't spec'ed to put out that much current. That said, I doubt it needs that much current in reality. I did this same mod to my cell phone years ago.

Yes, if you do plug-in 5volts to the charger jack, AND a usb cable the power will pass out of the USB connector.

[YoDude]

For those trying this at home...

A "Husky" brand multi tip torx screw driver is available at Home Depot in their tool coral for about 6 bucks.

Wooden cuticle pushers found in pharmacies (5 pack about a buck and a half) can be used as plastic pry tools.

:)

[paulh]

Nice posting, but on a cautionary note, I recently repaired a laptop power socket and accidentally desoldered a couple of those ferrite things. Took me about an hour to get them back in place.

[Nunim]

Very nice Howto, thanks for the effort !

For tinkerers who don't have the guts to disassemble their tablet, or don't "do" precision soldering, perhaps a modified USB cable with a tip that goes into the charger connector would be a simpler approach, with almost the same result ?...

They already sell these cables on ebay for sub $5, it would be simpler to just buy one. I like this idea but I'm not sure if I trust myself enough to attempt it :)

[Slakker]

So...

Does this mod also allow the 770 to use any old USB keyboard without macgyvering in a separate power source for it?

[ZapWizard]

Wooden cuticle pushers found in pharmacies (5 pack about a buck and a half) can be used as plastic pry tools. :)

Great tip, I never thought of that, I have to go get some now.

Nice posting, but on a cautionary note, I recently repaired a laptop power socket and accidentally desoldered a couple of those ferrite things. Took me about an hour to get them back in place.
The only reason I knew it was a ferrite was because it was gray, brown are usually capacitors, and parts like that with printed numbers are normally resistors. Just FYI.

So...
Does this mod also allow the 770 to use any old USB keyboard without macgyvering in a separate power source for it?
No, since the 770 doesn't send power out the USB in the first place.
(Unless you do as robbh66 asked)

[Slakker]

Ah...right...would it be possible to solder a wire from that ferrite to another pin on the USB and have it send power out the port?

[Bree]

I'm with slakker on this one.... what internal mod to get an ipod running as an external drive... ie power to usb?

plus flash to host mode...

[ZapWizard]

Even if the Nokia 770 generates +5volts for it's own circuitry, it would be a bad idea to try to tap that power for external USB devices.

There are a couple reasons besides battery drain:
-External USB devices could pull much more power then the 770 could provide (not due the battery life, due to the internal power regulators output)
-There no protection on the USB jack if a device were to pull too much power, or short out. (Normal USB jacks on PC's have this protection)
-Most of the internal circuits on the 770 probably run off 3.3volts not 5volts.
This allows them to work most efficiently off a lithium battery.

So you will still need to do the external power injection modifications on the 770 in host mode, as has been posted in the forums before.

[Bree]

ok..

I've been through all those earlier mods.
I just thought this one would work for an ipod as it already has it's own built in battery.... thus shouldn't pull power down from the n770 but might make the ipod accessable as an external drive...

???????????/

Any thoughts?

[Slakker]

I would think that perhaps the 770 would just charge itself off of the iPod battery...

[Bree]

that would be helpful in its self....

back up battery supply for the 770 from the ipod.... but could the ipod be accessed from the 770 if you flash the 770 into host mode?????

[Slakker]

If it's not accessible without this mod, I don't see how this would change it.

[ZapWizard]

I get what you are asking, but neither the 770 or ipod usb ports were designed to output power, they are power imputs.
Host mode changes the 770 so external devices can link to the 770 as any other linux computer, but it wont change the way the charger circuit works.

[Bree]

yeah...

but going back to ThoughtFix's powered USB hack using 2 cables to tell the n770 that there was something attached to the usb... the whole point was about getting power where power wasn't?????????

I'm I on the right track?

So I thought this mod might fix the same issue.

ZapWizard....Did you try it?
can you try it for us?

[ZapWizard]

I have connected both the charger cable and USB cables at the same time, nothing screws up, but I don't use my 770 in host mode, but here is no reason it should not work.
Just don't put too much stuff on the USB port (hubs, etc.) as that thin wire isn't made to carry much current.

[torx]

Hardware modders are rare around here. Glad to have you.

[synaps3]

I would seriously advise against using the internal battery as the power source for exterrnal devices. The battery is not designed to output enough current to power anything other than the 770... Overloading it could lead to either a leaky, hot battery or an explosive battery. At the very least, the battery will die quickly from strain...

[tarvoke]

surprised that no one else suggested this: you may want to add diode, protect usb from being fried.

not sure if the signal at the component you soldered to is more regulated vs. the charging pin, but it doesn't hurt to be safe.

the charging circuit will probably tolerate ~4-9V, because that is about the range that it can potentially see from even the official wall-plug charger.

[ZapWizard]

Good tips, a diode (1N4004 or similar would keep separation between the USB 5volts and the charger 5volts. It is also a safer way to do this mode if anyone is worried. But also most USB jacks are far more regulated then any wall-wart.

The Ferrite had 0-ohms continuity to the charger pad. But I am sure I am on the right side of the ferrite, as the cap next to it is connected to the ferrite and ground.


-Off topic...
I cannot for the life of me determine how the 770 detects that the cover was put on one way or the other. There are no contacts, micro-switches, and no magnet sensors that I can find.

[misterbleepy]

-Off topic...
I cannot for the life of me determine how the 770 detects that the cover was put on one way or the other. There are no contacts, micro-switches, and no magnet sensors that I can find.

I just spent a couple of minutes waving a fridge magnet over my 770 - the screen goes blank when the magnet is over the lower left side, around the left edge of the 'menu' key.

I'll leave the internal inspection to someone more adventurous than me ;-)

[tarvoke]

Good tips, a diode (1N4004 or similar would keep separation between the USB 5volts and the charger 5volts. It is also a safer way to do this mode if anyone is worried. But also most USB jacks are far more regulated then any wall-wart.

good point!

one might want to be a little more careful using e.g. wall-wart charger where the tip is mini-B (got a usb-charging camera, where they were nice enough to include one of these things as an accessory)
not to mention those car lighter plugs that have a female usb A port (voltage there will be all over the place I bet)

but... a diode may drop up to ~.5V, result could be below the min charging voltage the nokia needs to see. I may give it a try.


-Off topic...
I cannot for the life of me determine how the 770 detects that the cover was put on one way or the other. There are no contacts, micro-switches, and no magnet sensors that I can find.

try finding the magnet in the metal case, check corresponding location in the unit? from what I've read it is supposed to be a magnet switch.

[robbh66]

The reason Nokia probably didn't do this from the beginning is because technically the charger is rated at 900mA of output, and a USB port isn't spec'ed to put out that much current. That said, I doubt it needs that much current in reality. I did this same mod to my cell phone years ago.


I've never really been able to get a straight answer out of someone regarding electrical currents. Why is it volts need to be somewhat precise but amps can be tinkered around with?

[ZapWizard]

You don't actually control current. Current, measured in amps, is PULLED by the device. So you really only have control over the voltage.

Take the example of a 50-watt light bulb and a 100-watt light bulb.
Both run on 120-volts, but the 50-watt pulls less power, as the filament inside has more resistance to the flow of electricity (and generates less light)
The 100-watt however pulls twice as much current, as it has half the resistance, and converts twice as much current into light.

The 770 wall adapter CAN put out 890mA, but your 770 may not pull 890mA of current. But if you doubled the voltage, without increasing the resistance, then the circuit WILL pull twice as much current and then something fries.

The 770 would pull the most current if you were charging a dead battery and running the unit at full power (playing a movie over wifi for example)
But if it is just sitting on the desk, then it may consume only draw 100mA or so to keep the battery charged and the processor idle.

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If the basics of voltage/amps/power/resistance were never explained to you here is a dirty crash course, it's off topic but hey it's educational.

Think of electricity as water.
Think of a water tower as a battery
The water tower works by raising the water level above the ground.
That is Voltage. The potential amount of energy you can use.
So a 100-foot water tower could equate to 100-volts of potential energy.
A 5-foot water tower would be 5-volts.
A dead battery is like a empty water tower.

If you want to know what voltage really is: It is a measure of the distance the electrons flying around a atom are from their normal state (or distance from the center of the atom if you want)
The reason that high-voltages like lightning can travel a great distance is because the electrons move far enough away from the center of the atom that they can mix with the next atom nearby.

Voltage can also be equated to pressure. If you take a fire hose flow of water, and connect it to a garden hose...sure the water WILL flow through faster, but it will probably rip the garden hose to shreds doing it. (Like frying a wire)

Current is easier to understand, it is just like the flow of water. The more current, the more actual electrons that are flying by at the speed of light.
Cut you can't control how fast the water moves by, you can either slow it down by putting something in the way or you can reduce the amount of water that could enter the flow.

Resistance is like a waterwheel, or a tube. A water wheel takes a stored supply of water (voltage) and does something with it (grind grain in a mill)
A fire hose can carry a higher flow of water then a garden hose. That is why you need a thicker wire to carry a higher flow of electrical current. And that is why stupidly overpowered subwoofers need wire as thick as a pencil to work.

Power is a bit harder to understand for some people. Power is the amount of work being done, and the amount of energy wasted while doing that work. Electrically power is Voltage multiplied times the Current. Or the amount of current needed for 'x' amount of potential energy.

Google: Ohms Law for more.

[Jeffus]

First off, let me say, that this is a great thread. Zap, thanks for starting it.

I agree about not using power from the 770 to get the USB host mode working, as you can't internally limit the amount of current your devices will pull.

For those that don't want to solder internally, although it's really the smart way to go, you could get your hands on an old nokia power tip (an old phone charger, maybe?) and make a little USB-to-Nokia converter. That way, you just need to carry a tip, instead of a whole cable. Yes, again, it's just something to lose/carry, but it's an easy alternative. If I get a chance, I'll make one up, and let you know how it goes.

[robbh66]

Thanks Zap. I originally had a question which asked that- but i felt bad at getting you to write so much so I rephrased it to be a little more vague and simpler to answer- guess i got what I wanted anyways!

[ZapWizard]

No problem, as much as you are frustrated by not being able to get a straight answer, I am annoyed by electronics teachers who don't cover the basics with enough detail for people to understand why stuff is happening, not just that stuff is happening in a circuit.

[tarvoke]

For those that don't want to solder internally, although it's really the smart way to go, you could get your hands on an old nokia power tip (an old phone charger, maybe?) and make a little USB-to-Nokia converter. That way, you just need to carry a tip, instead of a whole cable. Yes, again, it's just something to lose/carry, but it's an easy alternative. If I get a chance, I'll make one up, and let you know how it goes.

this is a great idea. did the same thing for my iriver h140: radio shack sells a compatible dc tip; I took a retractable psp usb charger cut the tip off and soldered the ratshack tip on.

nokia tip is the smallest frikkin thing I've seen. not sure where to get one but hey lookee here I'ma hafta buy me some of this:
http://www.globalsourcesdirect.com/servlet/the-2486/Nokia-USB-Charger/Detail
(never bought from this place before but the price sure seems right...)

EDIT: hm oh wait they only sell it by the case. hell. time to look for a retail source.... /EDIT

[Jeffus]

this is a great idea. did the same thing for my iriver h140: radio shack sells a compatible dc tip; I took a retractable psp usb charger cut the tip off and soldered the ratshack tip on.

nokia tip is the smallest frikkin thing I've seen. not sure where to get one but hey lookee here I'ma hafta buy me some of this:
http://www.globalsourcesdirect.com/servlet/the-2486/Nokia-USB-Charger/Detail
(never bought from this place before but the price sure seems right...)

EDIT: hm oh wait they only sell it by the case. hell. time to look for a retail source.... /EDIT

Not a bad little cable. You know, I posted a deal earlier for this guy (http://www.dealminded.com/viewtopic.php?id=145). It has a Nokia tip and includes a car adapter, wall adapter, USB adapter, and 9 V battery in a portable package (so all those things could charge the 770). Sorry, this has gotten off-topic. If you think it will work, drop me a line @ the link.

[tarvoke]

I don't think it's off-topic; yes this thread is about ZapWizard's beautifully-documented hack, but it would seem a fine place to discuss alternate usb charging methods.

now that is one crazy device. I found another site selling it, that explicitly said non compatible with 770/n90/n91. which makes me question the compatibility of the cable on the link I'd posted.

[Kybo_Ren]

I agree about not using power from the 770 to get the USB host mode working, as you can't internally limit the amount of current your devices will pull.
Sure you can!
It just requires a little ingenuity and a trip to DigiKey :)
If you use a JFET and a resistor (or even better, two resistors that can be connected and disconnected via a switch) you could regulate the output current.

USB spec is 500mA MAX for USB devices. You typically only see this with long strings of devices or really really power-hungry devices. Most peripherals wouldn't need the full 500mA (hence the switch for two current ratings).
Since the charger is rated for 900 mA (apparently), the battery can handle at least that much current. When you figure the OMAP 1710 with its main core and DSP running at full speed probably around 200mA, wireless transmitting at full 20 - 30mA (100mW max), etc., your max current usage is probably around 400 or 500 mA, so even an extra 500 mA won't kill it.

[770gerd]

I don´t know about charging the N770 (and any other device) with a constant voltage source... I checked with a multimeter how the wall-charger charges the N770 and I found out it gives out a pulsing voltage and thus, current!

So my question is: May it be possible to harm the circuit board or the battery when using a constant voltage source?!

[ZapWizard]

@Kybo_Ren, A resistor does limit current pull, but it also drops the voltage output and as explained earlier there is no source of 5volts inside the 770.
The battery puts out 3.7volts. This is most likely regulated to 3.3volts.
The only reason the input voltage is 5volts is to allow for the regulator circuit to fast charge the battery.
So if you did want to run external USB devices on the 770, you would have to built and install a 3.7volt to 5volt DC-DC converter.

[Kybo_Ren]

@Kybo_Ren, A resistor does limit current pull, but it also drops the voltage output and as explained earlier there is no source of 5volts inside the 770.
You didn't read my post.
Read it and you'll understand ;)


The battery puts out 3.7volts. This is most likely regulated to 3.3volts.
The only reason the input voltage is 5volts is to allow for the regulator circuit to fast charge the battery.
So if you did want to run external USB devices on the 770, you would have to built and install a 3.7volt to 5volt DC-DC converter.

Sure, why not?
Last I checked there were a couple vendors selling cheap step-up transistor circuits with over 90% efficiency :)

[Kybo_Ren]

I ordered two samples of MAX756EPA+'s, and if they get approval, then I'll try my hand at a self-contained USB host mode hack.

[Texrat]

Kybo man! Good to see you join this forum. Hope you're enjoying your 770.

[Kybo_Ren]

You bet I am. This is seriously the coolest thing since... well... the internet :)

[Texrat]

Good to hear. Hey, I may have a nonfunctional 770 you can have to play around with, or use for parts if you like.

[Kybo_Ren]

Sure! More electronics never hurts :D

[Slakker]

You bet I am. This is seriously the coolest thing since... well... the internet :)

I concur. The few moments here and there I've been able to get WiFi (everything's hardwired here at home...three desktops, no need for anything wireless before the tablet arrived...hehe) I've loved it.

I convinced my boss to hook me in to the park WiFi, so I should get some decent face time with this thing soon. (I'm a lifeguard...yep, i'll be browsing on the job. I'll leave it up to you to decide whether or not i'll do it when there are people swimming)

[Kybo_Ren]

Just got approval for my samples.
I should get them within the week and then I'll try the hack.

[Texrat]

I scrounged together all my remaining 770 and N800 odds and ends. I'll get back with you via PM when I have identified which 770 to send you for experiments.

[Rtalian]

nokia tip is the smallest frikkin thing I've seen. not sure where to get one but hey lookee here I'ma hafta buy me some of this:
http://www.globalsourcesdirect.com/servlet/the-2486/Nokia-USB-Charger/Detail
You may want to check out my posts on this page (http://www.internettablettalk.com/forums/showthread.php?t=4154&page=3) about a smaller version of that cable.

[Kybo_Ren]

I scrounged together all my remaining 770 and N800 odds and ends. I'll get back with you via PM when I have identified which 770 to send you for experiments.

Alright, sounds good. I ordered two samples, so if at all possible I'd like to try it on a semi-broken or broken one first before I go messing with mine :)

[dcarter]

I concur. The few moments here and there I've been able to get WiFi (everything's hardwired here at home...three desktops, no need for anything wireless before the tablet arrived...hehe) I've loved it.

I convinced my boss to hook me in to the park WiFi, so I should get some decent face time with this thing soon. (I'm a lifeguard...yep, i'll be browsing on the job. I'll leave it up to you to decide whether or not i'll do it when there are people swimming)

dude, just throw the thing in a little plastic baggie (one with a ziplock)
and browse underwater.....the touchscreen does just fine through plastic!

I used mine for high-sierra cross country trekking GPS mapper with pre-downloaded topo maps in a ziploc baggie for a week!!

dcarter

[Slakker]

I do have her in a plastic bag when at work, though I'm not sure I trust a ziploc to keep my electronics safe when fully submerged...I've had a lot of bags leak liquid out of the inside...certainly not reliable enough for my beloved internet tablet!

[Texrat]

Alright, sounds good. I ordered two samples, so if at all possible I'd like to try it on a semi-broken or broken one first before I go messing with mine :)

I have 2 types of broken 770s: no power, and funky screen. Sounds like you need a funky screen. ;)

[tonydt1g3r]

1. so when you need to install a new OS it says unplug the 770, does that mean if you wire it up to charge from the USB port its not going to work right?

2. also is the diode really neccessary?

[Texrat]

Diodes can act to protect a sensitive circuit by ensuring current flows only one way. I think that was the intention in this case.

[Kybo_Ren]

I have 2 types of broken 770s: no power, and funky screen. Sounds like you need a funky screen. ;)
Yeah that'd work fine :)


1. so when you need to install a new OS it says unplug the 770, does that mean if you wire it up to charge from the USB port its not going to work right?

It would still work. Why wouldn't it?
Especially if you can switch the host mode and device mode.


2. also is the diode really neccessary?

As Texrat said, a diode ensures current only flows one way.
It would be easy to make an external switch that switches between two sets of diodes, each allowing current to flow different directions. That way you could have a device mode and a host mode (i.e. charge from a USB port mode and power devices mode)

[ishtob]

which direction shoul dbe diode be placed if there is to be one?

[Kybo_Ren]

Depends on what you want to do. Do you want to charge via USB or use the device as a host?

[barry99705]

Depends on what you want to do. Do you want to charge via USB or use the device as a host?


Yes! Some more stuff to make up for the ten character limit...

[Kybo_Ren]

Lol, if you want to do both, then just use them in opposite polarities :)

[ishtob]

i just want to charge the 770 by usb, not host usb

[Kybo_Ren]

Then put the diode in series (+ -> - -> + -> - is series) with the USB power input/battery line circuit.

[Kybo_Ren]

Actually, thinking about it, it would be better to put it in parallel. That way you get the same end goal but it draws less power away from the circuit.

[Texrat]

Maybe another example will help those who don't get the function of a diode.

A couple of years ago I had to build a device that detected when pressure was applied to an air supply hose and started an electronic timer to accrue how long the device attached to the hose had been used. That required a timer module, pressure transducer, 9v battery, a resistor and a manual switch. But wired with those devices alone, the logic had 2 paths to take to/from the timer module (one was always "hot" due to the battery) and thus I got dual states when I only wanted one. That meant I had to place a diode on one leg of the circuit to ensure that the logic only worked along the path I intended. Once I added the diode, it worked flawlessly.

[Kybo_Ren]

Maybe another example will help those who don't get the function of a diode.

A couple of years ago I had to build a device that detected when pressure was applied to an air supply hose and started an electronic timer to accrue how long the device attached to the hose had been used. That required a timer module, pressure transducer, 9v battery, a resistor and a manual switch. But wired with those devices alone, the logic had 2 paths to take to/from the timer module (one was always "hot" due to the battery) and thus I got dual states when I only wanted one. That meant I had to place a diode on one leg of the circuit to ensure that the logic only worked along the path I intended. Once I added the diode, it worked flawlessly.
That would only make sense to those versed in EE. Those who are well-versed in EE would already know what a diode does :)

[ishtob]

Maybe another example will help those who don't get the function of a diode.

A couple of years ago I had to build a device that detected when pressure was applied to an air supply hose and started an electronic timer to accrue how long the device attached to the hose had been used. That required a timer module, pressure transducer, 9v battery, a resistor and a manual switch. But wired with those devices alone, the logic had 2 paths to take to/from the timer module (one was always "hot" due to the battery) and thus I got dual states when I only wanted one. That meant I had to place a diode on one leg of the circuit to ensure that the logic only worked along the path I intended. Once I added the diode, it worked flawlessly.

wow, thnx! that makes more sense now... :P pardon my ignorance in the field of electroics... I'm just a med student

[Texrat]

That would only make sense to those versed in EE. Those who are well-versed in EE would already know what a diode does :)

hey, he said it helped him, so :p

[tonydt1g3r]

wouldnt be cool if you could supply power to the usb port then access a usb flash drive or something. that way you could store a bunch of movies and stuff on it or have multiple ones to store on them since the 2gb mmc isnt enough. does this sound feasable

[murphy]

I made the modification for my n800 and it's working 'quite' great :

- when I plug the normal power cable, it detects usb connection and unmount all my cards !
- also when I plug the usb adapter, the cards are unmounted... but I need them ! (ex : with Maemo Mapper)
Is there a way to prevent unmounting cards when you plug usb cable ? (by software configuration)

- I leave it plugged all the night(6-7hours) but it was not fully charged ?! strange...

http://keepi.free.fr/11863938928.jpeg

http://keepi.free.fr/11863939383.jpeg

- there is also an icon bug (the left one ; maybe normal, I never tried usb cable before) :

http://keepi.free.fr/11863946154.jpeg

[Kybo_Ren]

I think the easiest way to disable the unmounting would be to disable (or put a switch on) the thing that detects if there is a cable plugged in.

[phatman81]

Hello all!
(been out of the 770 game for a while, but i think its time to come back)
A question in refrence to this mod...
If in addition to putting the cable in to allow the unit to charge (with diode), what if you put an additional cable (with diode) from the charger tip connector to the same conenction on the USB port? Would this enable the unit to charge from usb while also allowing power to be supplied to a USB powered device, if the wall charger is plugged in? (and no, not at the same time... but this way you would not need a switch to change between diodes?)

[wassabi]

I like that idea. If you put a diode in the proper direction from the charger to the USB you could power the USB line to enable USB host mode.
Just plug the charger in when you want to use USB host mode and unplug the charger when you want to connect the USB to a PC.

Sounds like it would work great.

Expanding on that with a switch and a second diode for USB charging as well, I don't feel so good about that. Do you have a SPDT switch in mind? Where would you place it?

[phatman81]

I did the mod(sans diode and just the one wire), and it does charge the deive, but when i also have a card inserted, i get a constant usb connected/not connected (constantly switching back and forth). if i remove the mmc, it just charges with no error.
Any ideas?

EDIT: Well, i took out the MMC and reinserted, and now it seems to be working fine. I guess it was not fully inserted when i put it back in after install... very weird. But it now works 100%. can read it from the device or from windows while charging. Thanks again! :D

EDIT2: I let the device charge all day from almost dead (well, 6+ hours) and it was still charging. It does show full, but i guess the amperage from the USB port is not enough to fully charge LION. I will continue to experiment, but definately a worth while mod.