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ZapWizard |
2007-07-02
, 21:39
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Posts: 13 |
Thanked: 4 times |
Joined on Jun 2007
@ Austin, TX
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#31
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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.
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2007-07-02
, 21:55
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Posts: 15 |
Thanked: 1 time |
Joined on Jun 2007
@ cape cood
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#32
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Originally Posted by 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.
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.
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/s...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
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2007-07-02
, 22:25
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Posts: 17 |
Thanked: 2 times |
Joined on Jun 2007
@ IN
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#33
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Originally Posted by tarvoke
Not a bad little cable. You know, I posted a deal earlier for this guy. 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.
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/s...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
__________________
my site -> always looking for tablet deals! For example, cheap bluetooth gps units.
my site -> always looking for tablet deals! For example, cheap bluetooth gps units.
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2007-07-02
, 23:39
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Posts: 15 |
Thanked: 1 time |
Joined on Jun 2007
@ cape cood
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#34
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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.
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.
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2007-07-04
, 09:46
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Posts: 20 |
Thanked: 0 times |
Joined on Jul 2007
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#35
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Originally Posted by Jeffus
Sure you can!
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.
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.
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2007-07-04
, 10:53
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Posts: 7 |
Thanked: 0 times |
Joined on Dec 2006
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#36
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I donīt 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?!
So my question is: May it be possible to harm the circuit board or the battery when using a constant voltage source?!
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2007-07-04
, 20:31
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Posts: 13 |
Thanked: 4 times |
Joined on Jun 2007
@ Austin, TX
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#37
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@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.
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.
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2007-07-04
, 22:10
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Posts: 20 |
Thanked: 0 times |
Joined on Jul 2007
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#38
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Originally Posted by ZapWizard
You didn't read my post.
@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.
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.
Last I checked there were a couple vendors selling cheap step-up transistor circuits with over 90% efficiency
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2007-07-05
, 23:11
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Posts: 20 |
Thanked: 0 times |
Joined on Jul 2007
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#39
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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.
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2007-07-06
, 00:04
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Posts: 11,700 |
Thanked: 10,045 times |
Joined on Jun 2006
@ North Texas, USA
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#40
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Kybo man! Good to see you join this forum. Hope you're enjoying your 770.