Power and Navigate NUVI from USB out of the car.

 

I put this idea in another post but it was lost there.

I want to take my NUVI 250W on a trip where I have no access to a 12V charger outlet while in navigate mode. The solution appears obvious - use a 5VDC battery box. I now have one of those with a USB female plug output but turns out to be far from that simple.

The Problem.

Any standard USB to mini-usb cable will charge/power the NUVI from any 5VDC supply (including my battery box) BUT the standard usb - mini-usb cable is special to the NUVI. When plugged to a standard cable the NUVI thinks it is in MASS MEDIA MODE takling to a computer - NOT navigation mode like if it was on car charger power. A particular type of USB to mini-usb cable is required (X pin to 4 pin 17.3K ohm for the techno types) but does anyone build something like that - can not find one and how do you make one? Where is the B#*! 200K ohm resistor to replace!!!!!?

I had an idea.

Has anyone tried cutting the car charger cable and inserting USB female/male plugs into the line? Male plug would go into my 4xAA battery box OR the line out of the charger... Hot swappable power! And long enough to have the battery box in my backpack or wherever and the NUVI in hand. Should be good for 8 to 12 hours on one set of 4 AA NiMH batteries - and I have lots of those for my camera!

So - before I start hacking my car charger cable - any comments/hints/extra ideas.

GARMIN were no help on the matter - don't they think people want to use their units outside cars?

.

Does the Nüvi 2xx car charger produce 5V?

It *looks* like the same part as the StreetPilot C5xx car 'charger' - which is just a straight-through connection to the car's 12V system.

Also, will the Nüvi 2xx respond to the same trick as the Nüvi 3xx? ... i.e. plug in 5V source to side USB connector and let the unit enter mass-storage mode. Unplug connector and wait for it to start rebooting and then plug the connector back in. Second time, it boots as normal, but charges from USB.

--
------------------------ Phil Hornby, Stockport, England ----------------------               http://GeePeeEx.com - Garmin POI Creation made easy           »      

Works on 200W

Some people claim this is risky, but I have done it many times with no problem. I wait for it to say "Loading Maps" before I plug in the cable for the second time.

Hornbyp wrote:

Also, will the Nüvi 2xx respond to the same trick as the Nüvi 3xx? ... i.e. plug in 5V source to side USB connector and let the unit enter mass-storage mode. Unplug connector and wait for it to start rebooting and then plug the connector back in. Second time, it boots as normal, but charges from USB.

--
Dave - Garmin Nuvi 1390LMT.

pchinote wrote: Has anyone

pchinote wrote:

Has anyone tried cutting the car charger cable and inserting USB female/male plugs into the line? Male plug would go into my 4xAA battery box OR the line out of the charger... Hot swappable power! And long enough to have the battery box in my backpack or wherever and the NUVI in hand. Should be good for 8 to 12 hours on one set of 4 AA NiMH batteries - and I have lots of those for my camera!

If I understand you correctly, you'd still be running the Nuvi with your battery box, without the car charger's plug in the circuit. I suspect that the resistor involved in telling the Nuvi it's connected to the car charger, and not a computer, is within the plug. Most such car chargers have circuitry inside that, for example,converts the car's 12 volts to the necessary 5 volts. I suspect the Nuvi charger also has the necessary circuitry to keep the Nuvi out of "mass storage" mode. If I were doing this, I'd try connecting a USB cable to the battery box, and putting the appropriate resistor between the correct leads inside the box, to (as closely as possible) duplicate what the Nuvi sees when it's plugged into the car charger.

--
"Recalculating... drive 0.2 miles, then abandon vehicle." ------------- [ETrex Venture CX; Nüvi 40; Drive 52]

USB Power

pchinote-
I am not sure if the 660 has the same setup but it does use a standard USB to mini cable. I can't imagine Garmin using a "special" usb cable. That is the whole point of the 'universal' in universal serial bus (USB).

Power from the car charger (on the 660 at least) is provided to the windshield mount/cradle through the contacts on the back, NOT through the usb cable. That is how the Garmin knows it is not attached to a computer.

Sorry if I am sticking my nose in but I thought that maybe you were overlooking something. If I am off base I apologize and continue your discussion...

The Nuvi 2xx series does not

The Nuvi 2xx series does not have a cradle, per se. Just a mounting bracket, with no connections to the Nuvi. There is one USB female connector on the Nuvi, which is used both to connect to a computer (via a standard USB cable), or to the cigarette lighter in the car (via a car charger that terminates in a USB plug). So you're right, there is no special Garmin USB cable, but the Nuvi will go into mass storage mode if it's connected to a computer, or to a generic car charger with a USB connector.

--
"Recalculating... drive 0.2 miles, then abandon vehicle." ------------- [ETrex Venture CX; Nüvi 40; Drive 52]

Comments on Power and Navigate from USB out of the Car - 1

Thanks for the thoughts - I will try to answer a few questions.

The NUVI 250W car charger does produce 5VDC. If the NUVI gets more than its operating voltage it does not work - and that is great because that keeps the magic smoke in. Those non-NUVI cables that are direct 12VDC to the unit would be no help - and might cause magic smoke.

The cable is a "special" cable - see http://pinouts.ru/GPS/garmin_nuvi_power_pinout.shtml for the pinout. (as indicated - it is all to do with the resistance between the X pin and the No4 pin).

It is not possible to do that resistance at the other end (in the battery box) because the other end is a standard USB 4 pin - I suspect there may not even be 5 wires in the cable which does limit where the resistor can be (and make very difficult any mods). In the car charger output there is (appears to be) only the positive and negative wires (pins 1 and 4 I believe) - there does not appear to be a third wire at all into the car charger.

I am not keen on the plug in/out/in idea - potential cause of magic smoke escape - and if you loose ANY amount of the magic smoke..... Very Expensive Stuff to put back!

I hope that answers all the questions/ideas to date. Still waiting to find out if anyone has done the cable cut idea - if not I could be the first one to try.

Any more questions/ideas?

Musings...

pchinote wrote:

The NUVI 250W car charger does produce 5VDC.

I think I was confusing it with the 6xx and 7xx. On closer inspection, it looks more like the 3xx arrangement (but without a cradle connection).

Quote:

If the NUVI gets more than its operating voltage it does not work

Sounds like a Nokia phone ... "Not Charging" ... now what's that mean... wink

Quote:

Those non-NUVI cables that are direct 12VDC to the unit would be no help - and might cause magic smoke.

They don't have a mini-usb plug anyway - it's a larger, flatter thing.

Quote:

It is not possible to do that resistance at the other end (in the battery box) because the other end is a standard USB 4 pin - I suspect there may not even be 5 wires in the cable.

Have a look at this:-
arrow http://www.maplin.co.uk/module.aspx?ITAG=FAQ&ModuleNo=43998&...
One of the FAQ's says that the 'screen' is the 5th pin...actually that's Pin 4 on the pinouts.ru diagram.

I have a dead C510 here - and I can get at the connections at the back of its usb socket. Pin 4 is shorted to the screen - and none of the cables I've plugged in have a built-in 200K resistor. I think that a normal cable's Pin X is actually open-circuit (although it's quite fiddly to connect the meter and I could be mistaken).

Quote:

In the car charger output there is (appears to be) only the positive and negative wires (pins 1 and 4 I believe) - there does not appear to be a third wire at all into the car charger.

This would have to mean that the screen is utilised for supplying power - and that doesn't quite feel right, does it?

Quote:

Any more questions/ideas?

How about increasing the voltage of your battery box - and utilising the standard Garmin adaptor to run the Nüvi? You might not need to go all the way to 12V...though of course, you have to allow for the voltage dropping as the cells discharge.
And you could always go the DC-DC inverter route...

--
------------------------ Phil Hornby, Stockport, England ----------------------               http://GeePeeEx.com - Garmin POI Creation made easy           »      

Yes

Hornbyp wrote:

How about increasing the voltage of your battery box - and utilising the standard Garmin adaptor to run the Nüvi?

This sure sounds like the safest way to avoid magic smoke. grin Motorcycle battery in an over-the-shoulder bag with a standard cigarette lighter plug. Five minutes to get running and no warranty issues.

--
Nuvi 660 -- and not upgrading it or maps until Garmin fixes long-standing bugs/problems, and get maps to where they are much more current, AND corrected on a more timely basis when advised of mistakes.

Comments on Power and Navigate from USB out of the Car - 2

Success!

I now have an external battery set (4 x NiMH AA) powering AND charging my NUVI 250W AND in Navigation mode so I am no longer totally dependant on the car charger.

The solution was as I thought. Cut in a Female/Male pair to the car charger cable. Female off the charger and male on the cable. Now I can plug the male end into my battery box OR the car charger AND I get NAVIGATION mode NOT Mass storage mode.

Turns out that the car charger cable is a single shielded wire - the shield is the ground (or negative) and the centre is positive. My only problem is that the standard usb cable I cut was very lightweight so using all thumbs to make the fine soldering job required to the heavier Garmin cable was a trial and it leaves a potential weak point.

This solution paves the way for the other ideas mentioned. A higher voltage battery with a 5VDC regulator would be a reasonable solution.

I still have to figure exactly where the NUVI decides that my battery box voltage is too high and will not play. Have only found this problem with batteries fresh from the charger so perhaps it will not be an operational problem as NiMH batteries always loose a little in storage. I did look at a regulator solution but the battery voltage with AA is too close for anything simple to work. I can always feed it slightly discharged batteries from my camera...

In case I missed mentioning the battery box source - see http://www.pressdigital.com.au/battery-bank-with-switch-blac... - may not be the only one out there but it works.

Why include not a 7805?

pchinote wrote:

I did look at a regulator solution but the battery voltage with AA is too close for anything simple to work. I can always feed it slightly discharged batteries from my camera...

Would not a simple 7805 regulator in the battery box accomplish what you want? It would throttle back your battery output to exactly 5v. It would also allow you to build a more robust battery pack such as using 8 cells, etc.

To regulate or not (voltage)

The simple answer is that the 7805 type regulator will work if you have enough volts to drive it (see http://www.tkk.fi/Misc/Electronics/circuits/psu_5v.html) where they say (input voltage muts be at least 3V greater than regulator output voltage ot otherwise the regulator does not work well) muts? It was the first one I found smile but there are more that say the same ... anyhow you get the message.

My little battery box fits 4 x AA and I like that because I already carry the necessary charger and have a supply of NiMH AA for my camera so I am stuck with output from 4 x AA as by far my best option - as I indicate - a short use in the camera will bring it down to USB voltage. Starting from scratch - go the 12V and regulator or just the car charger - more weight and volume but probably days of kick.

An electronics geek can probably design a circuit with switching so that a regulator device is only active above USB voltages (5.5VDC I think) and there are most likely much smarter regulators available - LDO types perhaps???

Quick and dirty cheat

Yeah, I thought about the input requirement of 2-3v after I posted. A really quick and dirty cheat I have used in several projects is to use a diode in the + line. A diode produces a uniform voltage drop of about .7 volts regardless of the current. Need to drop the voltage 1.4 volts? Put 2 diodes in series. Doesn't limit current like a resistor would. Just use a diode rated at 1A or so. Problem with that approach of course is that when your battery voltage drops to 4.7 volts, the output would be only 4.0 volts.

Quick and dirty cheat - and a fix?

Switch it so that (if you remember) you bypass the diode as voltage drops in USB range? Might take a little trial and error.... but who said we were not inventive little navigators?

.

pchinote wrote:

My little battery box fits 4 x AA and I like that because I already carry the necessary charger

Yes that box looks quite neat - but a bit of a tight squeeze if you want/need to start adding switches etc.

Quote:

I am stuck with output from 4 x AA ... - as I indicate - a short use in the camera will bring it down to USB voltage.

The NiMH's fall to 1.2V per cell very quickly after any sort of use. They very slowly tail away to about 1V before eventually nose-diving to 0.4V or so. It would be interesting to know the point at which the Nüvi declares there is too little input voltage. I wouldn't have thought that 4V would be enough...so you're not going to get the full use of the battery pack.
I'm beginning to think, that having to 'pre-flatten' the batteries and then getting only part of their charge, might not be an ideal solution sad

Quote:

Starting from scratch - go the 12V and regulator or just the car charger - more weight and volume but probably days of kick.

I felt the urge to make myself something like this - and idly picked up a 4-cell 'battery box' I had lying around, as a starting point. This box is actually a detachable add-on, from a cheapo mp3 player 'dock' (The amp part is currently hardwired into the Landrover!).
Anyway, I inserted my 4 AA cells and stuck the meter on the two brass contacts at the back - result = 9V !?! After checking with a second meter(!) and confirming this was correct, I took this box to pieces. It contains a voltage-doubling circuit, already in-situ! So, the addition of a suitably rated 5V regulator and I'm ready to go smile

I was trying to find a way to somehow 'attach' this box to the Nüvi...then I realised I was slowly reinventing the Streetpilot smile

--
------------------------ Phil Hornby, Stockport, England ----------------------               http://GeePeeEx.com - Garmin POI Creation made easy           »      

not on my 200W

djohns18 wrote:

Some people claim this is risky, but I have done it many times with no problem. I wait for it to say "Loading Maps" before I plug in the cable for the second time.

Hornbyp wrote:

Also, will the Nüvi 2xx respond to the same trick as the Nüvi 3xx? ... i.e. plug in 5V source to side USB connector and let the unit enter mass-storage mode. Unplug connector and wait for it to start rebooting and then plug the connector back in. Second time, it boots as normal, but charges from USB.

I doesn't work on my 200w! May be I upgraded to 2.90firmware.

--
Dont drink and drive. Be aware of low flying aircrafts. Drive as fast as you can and go to Jail.

Keeping the volts up...

Returning to this thread, now that PaulATL has wandered off into the sunset (sunrise?), with his Solar Power Monkey smile
arrow http://www.poi-factory.com/node/11741

Earlier, I wrote:

Have a look at this:-
http://www.maplin.co.uk/module.aspx?ITAG=FAQ&ModuleNo=43998&...
One of the FAQ's says that the 'screen' is the 5th pin...

I bought a couple of these, to try and make the proper charging connector - but failed miserably. It turns out that Pin "X" isn't actually connected to anything! - you only get access to 4 pins and the screen. sad I'll go get my money back and see if I can find an alternative product.

and I wrote:

Anyway, I inserted my 4 AA cells and stuck the meter on the two brass contacts at the back - result = 9V ... It contains a voltage-doubling circuit, already in-situ! So, the addition of a suitably rated 5V regulator and I'm ready to go smile

Being disappointed with the 25 minutes I achieved with the direct output of 4xAAA NiMh's (because the voltage quickly dropped out of USB spec.), I returned to this approach (it being the probable implementation used by the Gomadic unit).

I added a uA7805SCP voltage regulator that I found in the 'bits box' and 4xAA NiMh cells(2700mA.hr). The result was a very encouraging 4.5 hours extra runtime (full brightness+bluetooth connected). Running the 7805 with no heatsink, results in a hotspot that needs dealing with, but otherwise it seems to be a workable solution - made from scrap wink

--
------------------------ Phil Hornby, Stockport, England ----------------------               http://GeePeeEx.com - Garmin POI Creation made easy           »      

How did you get a 7805 to work with 4xAA ?????

Hornbyp wrote:

I added a uA7805SCP voltage regulator that I found in the 'bits box' and 4xAA NiMh cells(2700mA.hr). The result was a very encouraging 4.5 hours extra runtime (full brightness+bluetooth connected).

Ok curious how you got that trick to work since a 7805 is a linear voltage regulator which normally requires an input voltage at least a couple/few volts higher than the output. Meaning a 7805 would require at least 7V input.

4xAA, even alkaline ones, would only be 6V or so when fresh.

???

PT

--
Garmin nüvi 200 (my first GPS), 780, & 3700 Series. And a Mac user.

.

Guttermouth wrote:

Ok curious how you got that trick to work since a 7805 is a linear voltage regulator which normally requires an input voltage

Ah - you need to read back a few posts...
That particular battery box contains a voltage-doubler (using the term loosely). It gives 9V o/p.

--
------------------------ Phil Hornby, Stockport, England ----------------------               http://GeePeeEx.com - Garmin POI Creation made easy           »      

Bad reading skills! :)

Hornbyp wrote:

Ah - you need to read back a few posts...
That particular battery box contains a voltage-doubler (using the term loosely). It gives 9V o/p.

Ah yes, now I see it. Sorry about that. Makes sense now.

PT

--
Garmin nüvi 200 (my first GPS), 780, & 3700 Series. And a Mac user.

Battery Box for the Garmin

I recently found a site that sells Battery Charger/Extenders (uses 4 AA Batts)for many GPSs:

Garmin - Mio - Magellan - Navman - Tom Tom

They also sell many other accessories for GPSs, Cell Phones, MP3 Players etc….

I purchased a "AA Battery Charge Extender for the Garmin Nuvi 750" and it was supplied with the proper tip (#73)so the Nuvi boots up in the NAVIGATION mode. I quess the X-PIN has the correct resistance Value!!

I tried it out with these results:

1. With the GPS on and in the Navigation Mode and screen backlight set to 20% and the Battery Backup Plugged in. I got 14 Hours and 22 Min. Before it went off due to low batteries.

2.With the GPS on and the GPS Simulator on and the Screen Backlight set to 20% with Battery Backup plugged in. I simulated following a route from my home in KY to NY City. I got 12 Hours and 5 min before it shut down.

The web site for this item and similar items is: http://www.gomadic.com

Hope you find this useful

I used another Battery Backup on my IQUE3600 over the last 4 years. It was used for my trips aboard the Amtrak where power outlets are sometimes not available. I track all my train trips on Amtrak and VIA in Canada so I can download the Tracks Log into MapSource on my PC. I can then view them either in MapSource or Google Earth. Now I will be able to do the same with mt NUVI750

H Hannah
Nuvi750 and IQUE3600

--
"Those that stop and smell the roses, must realize that once in awhile you may get a whiff of fertilizer."..copyright:HDHannah1986 -Mercedes GPS - UCONNECT 430N Chrysler T&C - Nuvi 2598- Nuni2555 - Nuvi855 - Nuvi295W - Nuvi 750 - Ique 3600

speed chargers

The gomadic.com web site has some interesting products. I like the fast chargers for both the car and house but wonder if there is a risk of damaging the internal battery in the Nuvi if it is fed too much juice. The standard charger that comes with the Nuvi is something like 280 maH while the advertised chargers are 1000 maH. Could it put the warranty at risk?

You are safe.

frobi2002 wrote:

but wonder if there is a risk of damaging the internal battery in the Nuvi if it is fed too much juice.

Nope. The charging circuitry is inside the nüvi which will regulate the voltage and current to the battery. The ratings of the charger don't matter that much assuming you don't exceed the max voltage of the charging circuit and that if the max current is lower than the max allowed by the charging circuitry it will just take longer to charge.

By the way, chargers are not spec'd by mAh as that is a unit of energy. Chargers would be in current (amps), voltage, and/or watts.

PT

--
Garmin nüvi 200 (my first GPS), 780, & 3700 Series. And a Mac user.

Quote I purchased a "AA Battery Charge Extender for the Garmin

grin neutral Quote I purchased a "AA Battery Charge Extender for the Garmin Nuvi 750" and it was supplied with the proper tip (#73)so the Nuvi boots up in the NAVIGATION mode. I quess the X-PIN has the correct resistance Value!!

I tried it out with these results:

1. With the GPS on and in the Navigation Mode and screen backlight set to 20% and the Battery Backup Plugged in. I got 14 Hours and 22 Min. Before it went off due to low batteries.

2.With the GPS on and the GPS Simulator on and the Screen Backlight set to 20% with Battery Backup plugged in. I simulated following a route from my home in KY to NY City. I got 12 Hours and 5 min before it shut down.

The web site for this item and similar items is: http://www.gomadic.com
thank you H. Hannah

I just looked at the address you put up and I must say it seems to fit everything that has been talking about with out losing the magic smoke. for you it is amtrak for me it is buses. since this company has all the Garmin pins sets for all the Garmin units I wonder in stead of getting a AA battery extender you could us other things like the APC - American Power Conversion APC UPB10 Mobile battery extender or other none AA source like a jell battery or Li-Ion rechargeable batteries. I like the AA's but more AA's every day means more trash more trash means more littering.
jolleyr c550

--
Southern CA Temp 76 and Sunny. Running around with my Nuvi 465T. Getting lost around the country and loving it.

How about a mini-usb to mini-usb with built in resistor?

I am a new Nuvi owner. Because I also own a Blackberry phone I have a mini-usb charger in each car. So I happily took off on a drive thinking that I could power my Nuvi with that charger. Of course mid-trip I found that I can charge but NOT power the Nuvi with that.

Once home I found that the AC charger that came with my Nuvi will let me power the unit while it operates. A bit of research with Google led me to this thread and the discovery that the Nuvi USB wiring uses the 17.3 K resistor to tell it to charge but not go into "mass storage mode". I would like to be able to skip dragging the Garmin auto cable with me.

It seems that all that would be needed is a simple mini-usb male to female cable a few inches long that passed power through and put a resistor across the pins on the GPS side. Does anyone sell such an item?

With the mini-usb power supplies becoming so common, including the little double AA battery powered devices you can buy to recharge cell phones, I can't quite believe that Garmin doesn't make it easy to use one of these to power the Nuvi while it operates. Seems like a poor design decision.

I don't intent to try building a cable, and don't know where to find a female mini-usb socket at anyway. If there is a commercial solution I would love to find a pointer.

More bits

daleoregon wrote:

Because I also own a Blackberry phone I have a mini-usb charger in each car...Of course mid-trip I found that I can charge but NOT power the Nuvi with that.

Have you tried removing the charger, so that the Nüvi reboots, then plugging it back in as the first screen appears. This works with some units.

and he also wrote:

It seems that all that would be needed is a simple mini-usb male to female cable a few inches long that passed power through and put a resistor across the pins on the GPS side. Does anyone sell such an item?

I managed to buy a plug, but there was no connection to the required pin sad The shop-assistant/store manager tried telling me I was trying to do something 'nonstandard'. I did a bit of research and found the official document that details mini-USB type B plugs. (Page 16, Table 6-2) in here:-
arrow http://www.usb.org/developers/docs/ecn1.pdf

Incidentally, the diagram at the pinouts.ru website seems to have the wrong pin designations.

They are:

PIN No. Signal Name

  1. ----> VBUS
  2. ----> D-
  3. ----> D+
  4. ----> ID (where the resistor goes)
  5. ----> GND

(and 'Shell') = Shield

(No mention of a Pin "X")

additionally, he wrote:

I can't quite believe that Garmin doesn't make it easy to use one of these to power the Nuvi while it operates. Seems like a poor design decision.

Of course, you could replace all your existing USB chargers, with Garmin's 5V mini-USB charger wink

http://buy.garmin.com/shop/shop.do?pID=1350

--
------------------------ Phil Hornby, Stockport, England ----------------------               http://GeePeeEx.com - Garmin POI Creation made easy           »      

Believe it (or not....)

daleoregon wrote:

If there is a commercial solution I would love to find a pointer.

You and me and a LARGE number of others as well just can not believe that GARMIN makes it so #$*%$ difficult to run any power to their machines and make them work anywhere!!!

Mini USB Plugs with 17ohm resistor

If you look at site:

http://www.gomadic.com/

You will find power adaptors for all Garmin GPS products including the Mini USB adaptor tip (#73)which has the built in 17ohm resistor.

I already have the Battery Charger/Extendar and it works properly. ( It came with the #73 tip for the Garmin Vuvi750)Costs $19.95 + SH of $5. Got it in 3 days.

I made sure the tip was the correct one, I talked to tech support and they confirmed that it did indeed contain the 17ohm resistor!!

Works great and lasts about 12 to 14 hours on a set of 4 AA batteries.

H Hannah
Nuvi750 and IQUE3600

--
"Those that stop and smell the roses, must realize that once in awhile you may get a whiff of fertilizer."..copyright:HDHannah1986 -Mercedes GPS - UCONNECT 430N Chrysler T&C - Nuvi 2598- Nuni2555 - Nuvi855 - Nuvi295W - Nuvi 750 - Ique 3600

The End

Some time ago I started this one and along the way developed a few ideas and went in a few different directions with useful ideas from contributors. Doing it the hard way can sometimes be fun - sometimes quite the opposite. I can confirm that the gomadic solution really does it and no playing with bits looking for where they hide the magic smoke! Works great and absolutely great service. I do hope they go on to make their No 73 tip with a 90degree bend (like the Garmin original so it fits snug against the Nuvi.

I think that is all there is to say on the subject.

Thanks to all.

Alternate solution

Might be very late...

I dug a lot about USB as I could not power and operate my Nuivi250 from an ordinary USB power (only) supply. This stupid box kept saying that it is connected to a computer, unless I was using the supplied cigare lighter cable.

First I looked at USB standards :
http://en.wikipedia.org/wiki/Universal_Serial_Bus
Then I discovered this interesting website about special USB mini B connectors :
http://wiki.openmoko.org/wiki/USB_charger
I then contacted Garmin support, but they seem to keep it secret.
This website solved the USB mini B socket problem: https://www.argentdata.com/catalog/product_info.php?products...
I ordered 3 cables and they ship them to France.
I built my own cable by inserting a 10k ohm resitor betwen brown (ID pin 4) and black (ground pin 5), the other cables beeing connected to the corresponding color of a USB A male cable.
Power is supplied by the USB source (computer or any power adapter) and the Garmin unit is working as a GPS.
Now I can have my computer in my car, and use the Nuivi 250 as a GPS, eventhought it is powered by my computer.
The +5 volts on pin 1 can alternately be supplied by any other mean such as batteries, regulators...

--
Jacques Bouchard Trouville France

Interesting

jacques.bouchard wrote:

Now I can have my computer in my car, and use the Nuivi 250 as a GPS, eventhought it is powered by my computer.

How are you powering the computer while in the car?

Thanks for the link to the 5 conductor USB-B Pigtail

I've got a need for all these pins to be brought out for different reasons here at work (totally unrelated to GPSRs) and didn't occur to me to look for a molded pigtail rather than a tiny solderable connector. Thanks!

Powering computer AND Nuivi 250 in the car

I discovered a very convenient power cord for my computer.
Input can be 110V to 240 V AC OR 12V DC from car or airplan (specific connectors included)

Output is some kind of a hub, delivering 20V DC for my computer and 5V via a USB A femal socket.
Other version can deliver 16V DC.
Here is the supplier (sorry, I worked for IBM during 40 years)
http://www-307.ibm.com/pc/support/site.wss/document.do?sites...

Hope this helps, Jacques

--
Jacques Bouchard Trouville France

Pigtail USB mini B

Good to know.
Jacques

--
Jacques Bouchard Trouville France

Charge or USB/data mode?

I will 2nd the Gomadic solution mentioned earlier. I have a tip #73 for charging. Tip #21 is for USB data connection (and charging). But in this application you need the charging tip... see below for an explanation.

Edit: I also have one of these to use the charging tip on:
http://www.gomadic.com/garmin-nuvi-1690-portable-aa-battery-...
(I bought it to use with my Edge 305 and found that it also works with my 1690)

Here's a link to the nuvi page.
http://www.gomadic.com/new-product-selector.html?product_sea...

I checked the 3790T and it has a different tip requirement (#90 for charging). The 765T uses a #24 tip. So Garmin does not use the same pin-outs across the board. Interesting. Apparently, I got lucky that my Garmin devices (Edge 305 and nuvi 1690) all use the same tip.

To help explain the difference between USB mode and charging mode, here is an explanation from Gomadic:

More about Step 3 'Charger' vs 'USB Cable' ...
You might be wondering why we ask the question “Accessory Type” in step 3. This is because some devices required a different pinout configuration for USB functionality vs just charging functionality. In these rare occasions that required different modes (USB mode vs Charge mode) you must use the right tip depending on the situation. This is why we ask what type of accessory you are using the tip with, USB Cable (transfer data) or Charger (ie car charger, wall charger, AA battery extender, charging station, etc)

Let me explain in a little more detail on what is going on with the different modes mentioned above. First it is important to know that most of the time the one tip will serve both functions but in some cases the manufacture of the device designed a two mode system. One tip is for USB Data mode with our USB cable product line. This tip is designed to connect to only the USB port of a PC. While connected it will both sync and charge the mobile device. The second tip is the charge only tip. This one is required when using the USB cable in conjunction with a USB Car or USB Wall charger. So in short if you use the USB data mode tip with a charger line product (such as a wall or car charger) than the device will never go into charge mode, this is because the tip put it in data mode and it will continue to look for data before charging. In this case you would have to use the charge mode tip to force the device to go into charge state. Again, most devices do not require the two mode tip system.

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nuvi 1690 with ecoRoute HD, SP2610 (retired), Edge 305, Forerunner 405

Battery cases

One caveat to the above post about the portable battery extender... AA batteries vary in diameter depending on whether they are alkaline, rechargeable, etc. Some batteries may be too large to properly fit.

If you buy a battery case and have trouble getting the batteries to fit, try a different kind of battery. I believe the rechargeables tend to be "fatter" than the non-rechargeable type.

While the difference may be slight, it adds up if you have 4 across and may make the battery door difficult to shut.

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nuvi 1690 with ecoRoute HD, SP2610 (retired), Edge 305, Forerunner 405

I had the opposite

I had the opposite experience. I bought the Gomadic charging wire hoping that it had that special "Garmin resistor" to prevent the unit from going to USB mode every time I start the car-- no dice.

Nope

I bought a Gomadic power adaptor because of this post.

Turns out, the power adaptor I bought does NOT have the 17 ohm resistor and the unit goes to USB mode every single time.

Not for the faint-hearted...

After reading this post, the first thing I did as electronics hobbyist, was to modify a lead myself: removed the plastic, soldered a micro resistor of 18 k inside and fill the thing with 2 component glue. This works to charge during navigation!
Unfortunately, after using it for some time it appeared that the plug was wearing too much and I did not want to go through the same process again.
I just managed to build in a very small DIP switch inside my Nüvi 760 to connect the 18k resistor to ground. It requires delicate soldering with a very fine tip soldering iron and it took me quite some time to get it right.
Now, when the switch is in position 1 it communicates to PC, in position 2 it charges from a car or mains adapter with navigation possible. This works nicely and I can use any charge cable now! Uhhmmm... not quite... I found that there are quite some cables that are OK for data communication, but their leads are so thin that they drop too much voltage and the charging voltage is simply too low.
Yet, for the time being I am a happy man! grin

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wwoef

USB version of power-only cord

Just discovered Gomadic also sells on Amazon, with free shipping.

Search for "SCC-2884" that is a nice coiled USB cable with the Gomadic tip #21 which is a standard mini USB (charge + data connect). I also ordered a Gomadic tip #73 (charge only) for my Nuvi 40LM. For about $24 total.

Links to these products:
http://www.amazon.com/gp/product/B002OIR8I8/ref=ox_sc_act_ti...
http://www.amazon.com/gp/product/B003KVPVUA/ref=ox_sc_act_ti...

Combining this with a Neewer AA battery charger and some good NiMH's to power my GPS on an extended bus trip (why luxury tour buses don't have 12V power outlets is beyond me!).
http://www.amazon.com/dp/B003VWU9LE/ref=pe_175190_21431760_M...

Haven't received & tested this combo yet. I went this route rather than the Gomadic battery pack so I can also use the USB cable at home or with a laptop to power-only the GPS similar to in the car.

Edit: Shortly after ordering on Amazon I called their direct # and they substituted the #21 tip (which I didn't need) for an Iphone charging tip for free!

Garmin Power Cord- SOLVED

Thanks to the posts on this issue, it made my job easier. The trick to making a Garmin Nuvi 350 cord with a male USB connector for the female side connector on the unit is even simpler than the discussion, although the ideas were really creative.
Taking a standard USB cord with the proper "mini usb" for lack of a better term and cutting that mini off, stripping the wires (btw guys, use a Paladin PA1011 stripper for small wires. They're expensive, but will save you more grief....worth it) reveals 4 colors and a standard coax shield. The trick is to put 5V on the unit, but not the typical red wire, black wire config. Put (+) Positive power on the SHIELD and the (-) Negative on the White wire. The unit will not go into computer connection mode and runs the Garmin just fine.
I have a ton of power supplies hanging around (don't we all) and I used a 5V car lighter cord from God-knows-what-unit from years ago. Simply join the cable by tinning and soldering the proper wires, above, but be sure to add a piece of small heat shrink tubing prior to soldering so you can make that joint tough. Black tape would do, but do it right, use heat shrink because its more durable.
The results are a long power cord, or any length you decide you want and you won't spend $29 at Garmin plus shipping for something that shouldn't be that expensive. Best of luck! Chad

IT'S EASY!

Jump the plug pin holes on the Garmin, no cord hacking required. The plug connector on the back has 5 holes that access the contacts for the mating mini usb.
With the unit upright, take a strand of wire and jump together the first holes from the left. It's that simple. The mystery to being able to navigate & charge with virtually any standard 5v mini usb ended supply is the need for the Neg. contacts to be one in the same. Standard cables,like the data cable that comes with the unit will put the unit into data because the Neg. contacts (5&4) are seperate. It's the secret of Garmin's ability sell so many "big buck" adapters.
Here is a fuzzy pic. http://img.photobucket.com/albums/v112/Phred501/IMG_2045_zps...

That does work, but you have

That does work, but you have to remember to pull the jumper when you need to connect the device to the computer. Otherwise, unless I'm mistaken the nüvi will enter navigation mode instead of data mode when you plug it into the computer since the power is shunted over to pin 5.

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"Anyone who is capable of getting themselves made President should on no account be allowed to do the job." --Douglas Adams