Magellan GPS - Re: A portable GPS should use standard mini-USB power (but which

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Re: A portable GPS should use standard mini-USB power (but which

Dale DePriest

2007-05-29, 12:33 pm

sarah bennett wrote:
> On Tue, 29 May 2007 01:52:05 +0100, Robert Peffers. wrote:
>
>
> Hi there Robert,
>
> USB is not just for computers. Think of it as a "universal power adapter".
> It happens to conform the the power supply requirements for USB, but
> there's no "data" in a power adapter.
>
> With a "universal power adapter" (ie the USB B power supply), you can
> charge your telephone, your earbud, your mp3 player, your camera, and your
> GPS ........ all from the same "universal power supply".
>
> This is so very important for portable electronics that I'm shocked that
> the GPS review web sites don't make it one of the number one criterias
> (after performance metrics, of course).
>
> Is there a web site that explains which power adapter is used by the
> various GPS units under test?
>
> sarah
>
>
It would be nice if this were so but it is not a universal power adapter
since the USB standard is _very_ limited in the amount of current it can
supply thus you can blow up your computer if you try and hook a device
that needs 2 Amps to a computer interface. For this reason there are
lots of tricks in trying to make a connector that can power your unit
and can also hook it to a computer. These tricks usually involve the
other pins in the device to try and make it be able to tell what kind of
power that is available. There is no standard for these tricks thus
there is no standard for USB power adapters, particularly when fast
charger or high current power is needed.

Dale
--
_ _ Dale DePriest
/`) _ // http://users.cwnet.com/dalede
o/_/ (_(_X_(` For GPS and GPS/PDAs

Dale DePriest

2007-05-30, 10:33 am

sarah bennett wrote:
> On Tue, 29 May 2007 09:45:22 -0700, Dale DePriest wrote:
>
> Hi Dale,
>
> I met you once in the south bay. IIRC, you worked for a software company
> and had a red compact car and lots of GPS units stuck to the dash with
> sticky tape! I thought it was neat that you tested GPS units on your own!
> You showed me every one!
>
> Anyway, do you have any idea why supposedly "in-depth" GPS reviews don't
> mention this simplest of all specifications?
>
> For example, even the Garmin Nüvi 680 "in-depth" (ha) reviews in "GPS
> Magazine" fail to mention what the power supply really is.
>
> Is this sad or am I missing something very basic in GPS units (perhaps the
> most basic specification there is)?
>
> sarah

Hi Sarah

This is a rather new feature of products. In the past there was never a
reason to mention the type of connector on the end of the plug as it was
assumed that you would use the power adapter it came with. As connectors
become more standard there has become a serious problem with power as
the mini-USB connector becomes standardized for portable devices. Even
if they mention the type of connector you still will not know if a
generic power adapter will work for the unit.

The basic problem is mA capability of the power adapter they give you
with the unit. If it exceeds 500 mA then it is likely that they have
modified it to provide protection for you laptop. This is due to the
basic limitation in power available from a laptop. Many GPS devices have
requirements for power that exceed the ability of a laptop to supply. In
some cases they have intentionally shut down the unit to avoid using too
much power. Another user in this thread already commented that "How
could they be so stupid to do this" but he clearly is clueless as to the
power needs of a device but this doesn't even slow him down at
criticizing. Other units make changes in the behavior of the device to
attempt to limit the power needs when hooked to a computer but the trick
is how to design the unit to detect whether it is hooked to a computer
or to a power brick. This often requires modifying the brick.

I suggest that, in your case, you suggest politely to the reviewers that
this is an important feature for you and that you would appreciate them
adding it to the review. Reviewers don't go to school or get any
training in doing reviews and many, like myself, are just volunteers.
However, as I said, having the connector, is not enough to meet your
requirements anyway and could lead to a mistake.

Dale
--
_ _ Dale DePriest
/`) _ // http://users.cwnet.com/dalede
o/_/ (_(_X_(` For GPS and GPS/PDAs

Ron Hunter

2007-05-31, 4:33 am

sarah bennett wrote:
> On Wed, 30 May 2007 07:37:21 -0700, Dale DePriest wrote:
>
>
> Hi there Dale,
> You're the GPS afficianado, so I take your word as Gospel. I do understand
> the 500ma limit of the PC and the 5V requirement of the unit and I think,
> by your words, that you understand why someone like I would want to know if
> the GPS unit allows a "standard" modern connection.
>
> Luckily, we're only talking about three things
> - connector & pinout (pretty simple - there only a few wires here)
> - supply voltage & current (pretty simple - eg 5v 500ma by the standard)
> - charge voltage & current (pretty simple - eg 5v 400ma or 5v 700ma)
>
> Since we're pretty much agreed on the first two items based on the USB
> specification, we're mostly left with the third. And, I think we're agreed
> that the third only "matters" when the charge current is greater than the
> supply current.
>
> In practice, this is pretty easily handled. Just bring a 750ma AC + DC
> adapter and all the units will be happy. My Blackberry, mp3 player, earbud,
> and camera all charge fine even with the 500 ma limitiation of the PC.
>
> While you can sense my frustration and shock that neither the reviewers nor
> the Owners Manuals detail these simple power supply specifications, I do
> understand that the volunteer reviewers are here to help us.
>
> I hope this thread gets noticed by at least one GPS reviewer who can then
> let us all in on the simple power supply secret of the NEXT GPS unit that
> undergoes a review.
>
> If we all ask the reviewers to at least provide a "yes/no" checkbox to the
> question below, we would have a BETTER GPS review. Adding the power
> requirement spec would be a little bit of effort for a much larger gain and
> no loss of data!
>
> IMHO, the modern world requires this question in all good GPS reviews going
> forward!
> * Does this GPS unit support the USB 2.0 mini-B specification (Yes or No)
>
> Otherwise, we're all forced to ask the question of each GPS unit under
> consideration. Having said that, I'm still unsure which nuvi units support
> the GPS specification for the AC + DC adapter! :(
>
> sarah

Sarah,
Again, read the manuals. They are online at the Garmin site.
It IS in the quick reference manual, although the full manual doesn't
seem to answer the question definitively.

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