Subject: Re: Garmin hackers : enlist here !
Newsgroups: sci.geo.satellite-nav
References: <3vd159$8eh@cicg-communication.grenet.fr>
Distribution: 

J. L. Longueville (jllongue@lepes.polycnrs-gre.fr) wrote:
: After the long discussion we've had about how we could try removing the 
: 99 mph limitation of Garmin 45, I think it is time to get organized, and 
: see if enough people are interested to keep the cost of the operation 
: reasonable.

Since I was stuck in town tring to get some work done without any power
or telephones (makes the computer kind of slow) I decied to start
on the project.  

Inital report:
The GPS45 is easy to get apart.  It can be put back together again, it
will be a bit rough arround the sides and it won't be water proof
but it will go back.  I expect that some palastic model cement might
work great.  Hot glue or PCV cement would be other choices.  Silicon
rubber seems to be what garmin uses to seal the units.

First postive result:
The case can be refilled with N2 if you have the right equipment.
I expect that a well equipted high school chem lab would have whats
needed.  There is a screw in the back of the GPS40/45 that is hiding
under the rubber strip.  This screw can be removed and the silicon rubber
seal can be broken.  At that point you could put it in a vaccum
jar and drop the pressure.  Fill the bell jar with Nitrogen and
repeat till you think you have the water out.  Water evaporates
real quickly if hte pressure is low enough.   Put more silicon rubber
on the screew and put it back in.

First negitve result:
There is no Flash RAM on the device!  Somehow I got the impression that
the part number of one of the devices was 28x020.  That would make
it flash RAM but the part number is 27x020 which makes it some flavor
of EPROM.  There is a sticker next to the board with its ROM
version on it.  The sticker is not on the chip.  This may be because
the program the rom while on the board or they didn't want the stickers
messing up the auto placment equipment.  I will have to find out
more about the part they use.

Next step:
The foccus now will be to completely document the Garmin/Garmin
protocol.  I have found that it will react to some random data
streams by locking up.  I plan on ordering a fan out adapter for
the 27x020 so that I can put it in my eprom reader.

Other deatils:
The board seems to be nicely laid out.  It uses three sections,
a digital, analog and power supply.  The digital section contains a
A dallas semiconducter device that I'm not sure of its function yet.
I expect that its the real time clock and maybe the internal temp
sensor as well.  It is next to a 32.768K cyrstal that I expect it
used for timekeeping but may also be used as a baud rate generator.
There is also a 74HC4040 which is is a high speed divide by two
device.  The power supply is a switching supply.  There are no
common regulators that I have found yet (but that doesn't mean
they are not there)..  The Analog section has a crystal marked
16.368 and some device in a cmetal box marked "Taiwan 1575B-14e"
with a large "e".  I expect this might be a amp or a filter or
both.  The circut layout has several winding paths.  Some of them
split off and join back and each branch has a different lenght.
The analog section has a device labeled "Garmin 5900000201,
IBM14R1608,64G0203" in a 44 pin package.  There is also one
adjustable cap and a 10 pin device "VU04 508"  Where the antenna
attaches it looks like there are some other options and there is
a fair amount of room on top of the board for something like a
patch antenna.  The board has 95% of the parts on one
side.  The other side has the RAM and ROM and pads for
several different types of RAM/ROM combinations.  The GPS45
uses two devices, but there is room for at least two more.

It basicly sounds exactly like the board Tom Miller described.
Anybody want to plug 40V into their GPS40 to find out if it likes
it?

Once last trick:
You can use your GPS45 as a volt meter.  It will tell you the voltage
of the internal and external power supplies while in the self test.
The temp reading seems to be calibrated in degrees C and the volt
meter seems to be calibrated as well.  (Hold enter when you turn it
on see these features).

More will show up on:
http://www.inmind.com/~thogard when I get arround to putting things
there. 

I need a volenteer who can convert photos to bitmaps.

-tim
http://inmind.com/~thogard GPS, VW and Usenet topics.  Vote for the VW groups.