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Setting up Navi GT31
up Navi GT31 for speed sailing by
GT31 firmware avaliable from this website is a firmware with extended
features, tested by Locosys, myself and other people, developed
to maximize the enjoyment of using GT31 in sport. These features
include Speed Genie, compact binary file formats, bio-feedback,
and nice screen font, among others. Please report any strange
firmware behavior here to assist progress.
Chosing SD card.
|Some brands/sizes of SD
cards may not be compatible with GT31. Check the readme.txt file
associated with firmware updates to see which cards you should avoid
and which cards were found to work fine. Make the test described
in section C1d.
B. Firmware Upgrade
the firmware upgrade procedure has changed
to become compatible with all firmware versions (V1.2 V1.3 and
V1.4) that are currently in use. New upgrade procedure is faster
and safer for your GT31 than the procedure previously
published on this website.
Before you begin your GT31 firmware upgrade, you need to identify
which "V" version of the firmware is installed in your
GT31. There are V1.2, V1.3 and V1.4 versions in use. Since Locosys
no longer maintains V1.2, it is not provided here.
All V1.2 V1.3 and V.4 varieties of GT31 firmware provide exactly
the same GPS-Doppler speed accuracy and performance, because they
use exactly the same code and parameters for the SiRF3 GPS-engine
inside GT31 (published here).
Firmware versions downloaded from this website after V1.2B1405
(after 14 May 2009) provide SDOP
data that is required for error-margin computations and Speed
Records. Later versions include bug fixes and various User Interface
improvements. Please read README file associated (and zipped)
with a version to discover what changes were made in respect to
The difference between V1.4 and V1.3 are a) different power-up
boot kernel and b) different memory range for Data Logger. For
this reason 2-file update is needed when upgrading to V1.4 from
lower V versions. All new GT31s have V1.4 installed by default.
Locosys states that "eventually" all GT31 units should
have V1.4. Locosys also says that there is no need to upgrade
to V1.4 if version that you currently use satisfies your needs.
Download the GT31 firmware:
GT31 V1.4: GT31_FW_V1.4B0803T.ZIP
GT32 (new twin-GT31) V1.4:
(works on plain GT31 too)
GT32 is a new 50Hz instrument that combines gps-Doppler
with inertial navigation technology. For details please see GT32-resource
1. After you downoaded
the appriopriate ZIP file above, you need to "unzip"
the content. The file with extension *.s is the firmware. V1.4
firmware has two *.s files, one firmware file and a GT31boot file.
After unzipping, please read README and UPDATE-INSTRUCTIONS files
2. Install GT31Updater
V0.71 or higher software, if not already
installed (it is included in zip archive)
USB-serial driver from GT31 CD,
if not already installed. The driver is necessary to communicate
4. Clear GT31 Data
Logger (DATA LOGGER>CLEAR>YES)
5. Turn your GT31
6. Remove the SD
card and find a tiny sliding switch "inside the card slot"
on the pcb, on "display side" of the card slot. The
switch has a black lever and metallic body. The default position
of the switch lever is labelled in white on pcb.
7. slide the switch
lever using a match or a similar object away from the white mark
8. As a precaution,
exit all Windows applications and disconect from Internet. Run
GT31Updater V0.71 (or later). Select
the correct COM port from the pop-up menu and choose "INTERNAL"
mode. Then use "browse" function to select and load
2 files that you unzipped in step 1, one at a time:
a) V31BOOT_V4D.s (you only
need to update this when upgrading to V1.4 from lower V versions)
b) V1.4 firmware
may be necessary to quit and re-start GT31 Upgrader V0.71 after
the first file update.
9. when Updater
finishes, disconnect GT31 from USB cable, move the switch lever
to its normal position, labelled white on pcb. Your GT31 should
be ready to use. Power in ON, go to Settings and select Version.
You should see the Version Number corresponding to the name of
the file in step 1 and 8b.
Prototype of fully
waterproof case for GT31/GT32. The case has wide angle of view
and 2 straps. When you use Speed Genie there is no need to push
any buttons when you measure your average speeds. Turning on/off
and basic manual operation is done using a magnet. Charging and
access to SD card requires disassembling the case using a screwdriver.
. GT31 Settings
There are 2 methods of setting-up Settings in GT31:
- manual: using buttons in GT31 itself
- using NavilinkII : this method enables you
to backup/share/restore complete set of GT31 settings. Download
my settings file and use NavilinkII>Settings>Write function
to load this setting file to your GT31. This setting file works
for V1.3 and V1.4 firmware listed above.
up GT31 manually
a. LOG SWITCH
should be ON-FIX. There is no point to log any data when there
is no position fix.
b. NMEA ITEMS should be set to "SBN
1 SEC", which is default for all "extended features"
firmware downloaded from this website. If you want the most complete
data set from your sailing session, use SBN (binary) format logging.
c. MIN SPEED should be set somewhere
between 2 and 5, unless you are specifically interested to log
data when you are stationary.
d. FORMAT CARD. Read readme.txt file
to find which cards are compatible with G31. Format the card a
few times in a row. If you succeed each time, you can rely on
the SD card that you use.
e. FILE SIZE should be set to CARD SIZE.
This means that you do not put any limit on file size.
It is important to set your name, so that data files are properly
b. SPEED AVG TIME = 10 seconds if you
am for 10s runs, or 21s if you aim for 500m world record.
c. SPEED GENIE =
between 20-to-30 knots (37-55 km/h if UNITS are set to m). SPEED
GENIE anticipates what you want to see. It automatically changes
SPEED screens, resets MAX and MAXAVG speeds so that you do not
need to push any buttons when you sail. SPEED GENIE is only active
in the SPEED menu. The 1-99 value in SPEED GENIE is a speed threshold
for activation of the real-time speed measurement screen. NEW:
Speed Genie automatically saves 14 MAX speeds and 10 best n-second
averages (n is set in 2b). You can RESTORE any value and make
a photo showing your speed achievement. When SPEED GENIE in on
(set to non-sero value) GT31 internal chipset parameters are optimized
for maximum possible accuracy and reproducibility in speed measurement.
Speed Genie Sound:
GT31 Speed Genie provides bio-feedback sound/light indicators:
acceleration, max n-second average speed increase and also audio-announces
the max avg speed result. Sounds are designed for GT31 mounted
inside the helmet to provide sailors audio-feedback so that they
can focus their eyes on sailing to improve safety and maximize
speeds. LED bio-feedback is designed for arm-mounted GT31. Set
(ALERT>SPEED GENIE>ON) to enable Speed Genie helmet bio-feedback.
If you need sound, set (ALERT>BUZZER>ON). The bio-feedback
is delayed about ~2 seconds, due to the limited bandwidth of the
GT31 Doppler system. Please see README file for details.
3. DATA LOGGER
Data Logger is an internal memory for GPS data logging, arranged
in a circular buffer that automatically overwrites the oldest
data when full. It has the capacity for ~4.5 hours of logging
GPS data every second with full precision. It allows Navi GT31
to be used without SD card. Set INTERVAL=1s. Setting MIN SPEED=5
helps to extend the logging time, because memory is not wasted
to store stationary and low-speed data.
You may wish to CLEAR the data logger content before each sailing
session. Before executing CLEAR please SAVE the content to SD
card. Using this method regularly ensures that you will have a
backup of all your GPS data on your SD card. Of course you can
back-up SD card content to your computer.
The most convenient way of clearing Data Logger and other GT31
data before each sailing session is to use MISC>DELETE>ALL>YES
function. This operation clears "best runs" memory too.
If you need maximum battery life, make sure that you set SETTINGS>BACKLIGHT>OFF,
because light consumes a large proportion of GT31 power. GT31
with BACKLIGHT=OFF has been tested to work at full accuracy and
with SD card for 25 hours continuously.
The most convenient functions of MISC are SAVE TO CARD and DELETE.
SAVE TO CARD - saves all GT31 memory items to SD card files. SD
card must be present.
DELETE - clears all GT31 memory and
Data Logger that have been saved using SAVE TO CARD
Using MISC items User can choose screens for Speed Genie result
Following screens can be enabled (ON) or disabled (OFF)
1. MAX/NS MAX - screen showing MAX run speed and best N-second
2. HISTORY MAX - screen thak compares current run with history
3. MAX SPEED - MAX speed of the run in LARGE font
4. NS MAX AVG - in LARGE FONT
When more than one screen is enabled (ON) they will appear in
a "rolling" sequence.
When you have only 1 second to look at all Speed Genie results,
enable only screen 1.
NEW FONT - enables highly readable Large font. Set it ON to enjoy
clearer speed display
6. OTHER settings
Other settings are almost irrelevant
for speed sailing. You may consider setting UNITS (NM or m), BACKLIGHT
etc... in SETTINGS to suit you.
your GT31. If you have set up the SPEED GENIE as in C2b - GT31
will enter the SPEED menu automatically after it established connections
with GPS satellites. SD card Logging activity is confirmed by
flashing log indicator. Move GT31 with speed above the threshold
you set in step C1c and check it.
You may wish to clear the "history" of your
best speed runs, to keep track of your best daily achievements.
The best way to do this is enter MISC menu and do 2 things:
1. SAVE TO CARD>SAVE ALL (this will save datalogger data and
best run history to SD card)
2. DELETE>DEL ALL (this will clear data logger and history)
USING TWO GT31
use two GT31 to measure the same speed you should take care to
put their GPS antennae as close to one another as possible. Since
GT31 antenna is located next to the joystick - this means that
when two GT31 are insterted into an aquapack - joysticks should
be close to one another. This means that one of the GT31 screens
will be "upside down". If you want to read both screens
right way up, use MISC>SCREEN FLIP settings to flip the "upside
down" screen for easy reading.
When you neglect to place two GPS antennae close together, each
GPS will read different speeds every time when there is rotation
of the GT31 pair and/or the distance between them changes. For
example when antennae are 10cm apart, and your arm that holds
them rotates 30 degrees in 1 second, the speed difference measured
by 2 units can be as large as 0.1 knot during your hand stroke.
The speed difference depends on the direction of rotation and
is typically smaller than 0.1 knots, but it is obvious that taking
care of keeping both GT31 antennae as close as possible is clearly
a step to improve the reproducibility of speed measurement by
enabling two GT31 to cross-verify and re-confirm readings of one
Another good way to ensure the reproducibility
and repeatability of speed measurement during sailing is to place
both GT31 units inside the
helmet. Not only GT31 antennae can be close together, but
also rotation stroke magnitudes are restricted, because human
head is subject to continous bio-feedback from the body to minimize
its motion, even if the rest of the body vibrates in bumpy chop.
GT31 used in a helmet experiences the best possible satellite
signal from the maximum possible number of satellites, which contributes
to increasing reproducibility and reliability of speed measurement.
The best way to improve reproducibility and repeatability of speed
measurements is to use GT32 (twin GT31).