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'[OT] An electronics puzzle'
2006\07\11@143741 by John Nall

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Here is a puzzle that a friend presented me with, over the weekend.  My
background is software, not hardware, and so I didn't have an answer for
him.  But I did tell him that I knew the perfect place to ask the question.
.
He has a fishing boat, with a canvas top.  The top was torn, he had it
replaced, and in the process the electronics had to be temporarily
moved.  When he got the boat back and turned on his GPS, it searched,
but never found the satellites.  Later, he found that all the stored GPS
numbers (e.g., locations of favorite fishing holes) had been wiped out.  
On the theory that something was wrong with the GPS unit itself, he
borrowed a similar unit from a friend, plugged it in, and it seemed to
work.  Except that after he gave it back,  the owner found that all of
the GPS numbers had been wiped out.  (The GPS units are connected to the
12 volt battery system).
.
Now,  in my analysis there are only four possible suspect. (A) A bad
antenna connection, or (b) reversed polarity, or (c) voltage less than
12V at the GPS unit, or (d) some combination these three.  I presume
that the stored GPS numbers must be in some sort of flash memory, since
they can be changed, entered, or deleted by the operator.   Since two
different GPS units were used, and both had been working fine, we can
probably assume that the units are OK.  A bad antenna connection could
cause the endless searching, but difficult to see how it would affect
the stored numbers.  Low voltage is a possibility, I suppose.  It is
difficult for me to see how reverse polarity could cause the problem,
but it may be that one of you engineers will pick up on that.
.
At any rate, there is the puzzle.  Any educated guesses??  And to answer
an unspoken, but obvious, question, this guy does not have a multimeter
and wouldn't know how to use one if he had it.  Strictly an appliance
operator.
.
John

2006\07\11@151426 by Kenneth Lumia

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----- Original Message -----
From: "John Nall" <spam_OUTjwnallTakeThisOuTspamgmail.com>
To: "Microcontroller discussion list - Public." <.....piclistKILLspamspam@spam@mit.edu>
Sent: Tuesday, July 11, 2006 2:37 PM
Subject: [OT] An electronics puzzle

A couple of guesses:

>When he got the boat back and turned on his GPS, it searched,
> but never found the satellites.

Bad antenna connection.  Check for corrosion.

>Later, he found that all the stored GPS
> numbers (e.g., locations of favorite fishing holes) had been wiped out.

Values stored in a ram chip.  Power loss = lost data.
Or, more likely the values were stored in a battery backed up ram.
Bad backup battery = lost data.  I suggest reviewing the owners manual.

Ken
klumiaspamKILLspamadelphia.net

{Quote hidden}

> --

2006\07\11@154418 by M. Adam Davis

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On many of the older units the data is stored on battery backed RAM.
If you don't change the batteries every few years (even rechargable
batteries), then when the unit loses power for more than an hour it
may lose or corrupt the data memory.

Alternately if the power is cut to the GPS while it is on and/or while
it is completing some sort of memory operation, it may corrupt the
data itself.  In this case even if it's on Flash or EEPROM if the
firmware is stupid it may decide to throw away all the data instead of
trying to recover the good data out of the corruption.

-Adam

On 7/11/06, Kenneth Lumia <.....klumiaKILLspamspam.....adelphia.net> wrote:
> {Original Message removed}

2006\07\11@161452 by Kenneth Lumia

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If both units were "old", both units may have a bad
backup battery.

Ken

EraseMEklumiaspam_OUTspamTakeThisOuTadelphia.net
{Original Message removed}

2006\07\11@190707 by Gerhard Fiedler

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John Nall wrote:

> Except that after he gave it back,  the owner found that all of the GPS
> numbers had been wiped out.  (The GPS units are connected to the 12 volt
> battery system).

I think the possible answers depend a lot on how exactly it is connected to
the battery -- both in your friend's friend's boat, and in your friend's
boat.

All answers so far point to battery-backed storage and bad backup
batteries. However, if the GPS unit is connected to a switched battery
connection and frequently disconnected from the battery for a long time, it
is unlikely that your friend's friend's unit had a problem with this that
he wouldn't have noticed earlier. Possible, but pretty unlikely. In this
case it is quite unlikely that it would have lost the locations due to
being disconnected while moving it.

Now if it is connected to an "always on" battery connection on that boat,
then of course the bad backup battery theory is quite likely.

Gerhard

2006\07\11@205201 by John Nall

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Gerhard Fiedler wrote:
> > I think the possible answers depend a lot on how exactly it is connected to
> the battery -- both in your friend's friend's boat, and in your friend's
> boat.
>  
.
Although I do not know the answer to that, since both of them have boats
with dealer-installed electronics (as opposed to having the expertise to
install their own electronics, as I would do) then the chances are quite
good that the GPS (and the other electronics) are powered from a 12V bus
and a GND bus, which in turn are connected through an ON-OFF-BOTH switch
to a battery.  That is pretty much standard.
.

> > All answers so far point to battery-backed storage and bad backup
> batteries.
.
Since I do not know the answer to the puzzle, I cannot unequivocally say
that these answers are wrong.  But I suspect  that they are.  People
with small boats customarily remove the electronics from the boat when
it is not in use, both for protection from the weather and protection
from thieves.  Neither of these units had lost the numbers before, and
the chances of both of them simultaneously having the internal
backup-storage battery go bad would seem to me to have a very low
probability.  (I do agree that they probably do have an internal
backup-storage battery, and RAM.  for the storage).
.

> > Now if it is connected to an "always on" battery connection on that boat,
> then of course the bad backup battery theory is quite likely.
>  
.
It is extremely unlikely that the batteries are "always on," since that
is not the practice of people with small power boats which may only get
used once a month or so.  A small thing left on will drain  the battery,
so people usually either turn the battery switch to off or physically
disconnect the battery.
.
Anyway . . .  I do appreciate all the good guesses.
.
John

2006\07\13@062047 by Howard Winter

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John,

On Tue, 11 Jul 2006 20:52:00 -0400, John Nall wrote:

{Quote hidden}

Actually, not necessarily!  My brother has a boat and I did some rewiring for him last year.  As you say there
are battery switches that allow the two batteries to be used together, independantly, or not at all, but there
is also a small "always on" feed which takes power from the "Domestic" battery (the one that isn't used to
start the engine).  This feeds connections on the GPS and the car-style entertainment radio, each of which
have separate power feeds for memory retention and operation.  The former is always on, has a small fuse, and
draws a tiny current which a 100Ah battery wouldn't notice, and the latter is controlled by the battery
switches and the DC panel, which has switches and circuit breakers for the various circuits.  The GPS he uses
is pretty old, doesn't have internal batteries, and does indeed lose all its waypoints etc. if the memory
retention supply is removed for more than about an hour (probably has capacitors that keep it going this
long).  I believe some of them even came with a car-connector harness which is used to keep the memory alive
when out of the boat, in a car or on a 12V supply at home.  

The boat-repairer may have removed the battery connections so the GPS lost its waypoints, and may have failed
to reconnect the "always on" wire, which will be a small one, easily missed when connecting the huge main
battery cable.  Get your friend to look at the batteries, and see if there's a small unconnected wire hanging
around nearby, possibly with an inline fuse in it.

Nowadays modern units tend to have batteries inside which may be rechargeable or just long-life lithium cells,
such as the CR-2032, or they use non-volatile memory such as Flash.

All the talk of bad antenna connections and such is irrelevant - no form of connection to an antenna would
affect the stored data, only its ability to find out where it is at the moment.

Cheers,


Howard Winter
St.Albans, England


2006\07\13@071623 by John Nall

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Howard Winter wrote:
>>
> > Actually, not necessarily!  My brother has a boat and I did some rewiring for him last year.  As you say there
> are battery switches that allow the two batteries to be used together, independantly, or not at all, but there
> is also a small "always on" feed which takes power from the "Domestic" battery (the one that isn't used to
> start the engine).
.
Obviously I do not know about the battery switch on your brother's boat,
but the battery switch on my own boat, as well as all the others that I
know of, will disconnect the "panel feed" wire when the switch position
is turned to OFF.  As you say, this "panel feed" wire normally goes to
the bus from which all the accessories such as GPS, radio, etc., derive
their power.  Whereas the main wire (or, more accurately, cable) goes to
the starter for the engine.  But I know for an absolute fact that my
battery switch will disconnect everything when turned to the OFF position.
.

> > The boat-repairer may have removed the battery connections so the GPS lost its waypoints, and may have failed
> to reconnect the "always on" wire, which will be a small one, easily missed when connecting the huge main
> battery cable.  Get your friend to look at the batteries, and see if there's a small unconnected wire hanging
> around nearby, possibly with an inline fuse in it.
>  
.
Had the panel feed wire not been connected, then the GPS unit would not
have powered on.  So I don't think that is the answer.  One person
suggested the possibility of an intermittent power connection such that
the internal software for the unit might not have functioned correctly.  
Although this does not make complete sense to me, it nonetheless makes
more sense than any of the other educated guesses.  :-)
.

> > All the talk of bad antenna connections and such is irrelevant - no form of connection to an antenna would
> affect the stored data, only its ability to find out where it is at the moment.
>  
.
I agree..
.
John


2006\07\13@120548 by VULCAN20

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For what it is worth my 2 garmin 45 XL GPS's sat for 3 months on one of
them and 14 months on the other they did not lose any of their way
points or other stored data.  Three were not batteries in either unit.

Bob

John Nall wrote:

{Quote hidden}

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