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

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...

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.

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.

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 ;-)

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.


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.

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?

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.

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.

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!