GPS interfacing notes for Mapper-3a/GB v3.8
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Connection of the GPS receiver to a Psion 3a running Mapper-3a.
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Required are:
* Psion 3a with 150k of free system memory
* Installation of Mapper-3a/GB v3.6 or higher or Mapper-3a/London v1.5
  or higher
* 3-Link cable (or customised part thereof, see below)
* GPS receiver with NMEA 0183 v1.5 or higher interface and data cable

Also recommended are power leads for your 3a and GPS if you intend
to run them both for long periods! Note that the Psion doesn't *have* to be
on all the time, you can just turn on when you need a 'fix'!

Installation instructions:
1) Exactly how you wire up your GPS to the Psion depends rather on which
GPS you've got and whether you're prepared to spend a few minutes doing
some soldering! It may also, in the future, depend on what Psion do to
change the 3-link lead to conform to new 1996 European regulations, but
there's nothing I can do at this stage to predict this, so I'll assume
you've got a 'standard' 3-link with 'podule'.

Option (i) Ready-made up lead from GPS to 3-Link podule
           --------------------------------------------
           I can supply a made-up lead from some GPS makes to the Psion
           3-link podule. Contact me by e-mail or telephone for more details.

       (ii) DIY wiring of direct GPS to podule lead
            ---------------------------------------
            All you need is the data cable for your GPS and a mini-DIN
            connector from somewhere like Tandy or Maplins. For pin wiring
            details, see the appendix in the 3-Link manual.

       (iii) DIY wiring using full 3-link cable
             ----------------------------------
             The quickest way to get up and running is to connect the GPS's
             data cable up to a convenient connector on your 3-Link. I made
             up a male 25 way connector for myself, but each installation
             will be different. Connect the brown (serial data out) wire
             from your GPS to pin 2 on the 25-way connector on the 3-Link.
             Connect the black wire (ground) to pin 7 on the 25-way. Note
             that if you haven't got a Garmin GPS, the wire colours may be
             different!

In terms of minimising bulk, the mini-DIN connector solutions are by far
the neatest, although soldering these small connectors is not an easy job,
and also the standard mini-DINs tend to need 'shaving' to get them to fit
the podule receptacle!

There is actually an option (iv), which is a dedicated GPS to Psion
opto-isolated lead containing the guts of the 3-link podule, made for
marine use by a firm on the South Coast. They charge about 70 quid plus for
it, though, so assuming you already own a 3-Link, it makes sense to use
this!

2) Plug the lead/3-Link into the 3a

3) Start up the GPS and position in your car to get good satalite
reception. I find it works very well wedged on top of the dashboard, but
if you have a heated windscreen this may be a problem for you, as the
mesh of wires can block the signal.

4) Start up Mapper-3a/GB and go to the map you want the moving map icon
displayed on-top of, and set your required sticky displays/options. If
you're wanting to try out the ETA/Distance left option, choose your
settings in the 'Moving Map Settings' dialog, and 'select' a destination
(place or overlay item) by 'find'ing it in the usual way. When all is
ready, select 'GPS Moving Map' from the right-hand menu.

5) If all is well, you'll see one of two icons on your map. Either a
cross-hair showing current position or a 'Poor GPS' icon. The latter will
appear whenever your GPS's output quality deteriorates to warn you that it
doesn't really know where it is anymore. Try waiting or re-positioning your
GPS ....

6) If the cross-hairs get too close to the edge of the screen, the map
will re-centre itself and stay in 'GPS Moving map' mode.

Have fun!

Steve Litchfield

Extra notes:

* If you haven't got a GPS yet, there is a little simulator routine built
into the program to show you what you'd see ..... If you need to buy a GPS,
I recommend the Garmin GPS-45 (try Pumpkin Marine on 0171 4806630), which
should cost about œ280 including the data cable and VAT ...

* If you should blow anything up or injure yourself in any way, please note
that I take no responsibilty whatsoever for use of this software product!
And if you're driving, keep your eyes on the road! I mean it! ONLY USE THIS
PROGRAM ON THE MOVE WHEN SOMEONE ELSE IS DRIVING. IF YOU *DO* USE THIS
ALONE ON THE MOVE, I WILL NOT BE HELD RESPONSIBLE WHEN YOU CRASH HEAD-ON
INTO A JUGGERNAUT!!!

* Technical one, this. Your GPS map datum should be set to WGS 84, if
it's not already! Also, the NMEA version supported by Mapper-3a is 0183
version 1.5. Mapper-3a gets its information from the NMEA sentence $GPRMC,
so if your GPS doesn't output this word you're stuck! Get in touch and
I'll see what I can do ....