[aprssig] Re: LCD in the car

Dave Baxter dave at emv.co.uk
Tue Mar 25 05:29:24 EDT 2008

>From more than a little personal experience with "in car PC's" for
several people (not ham related)...

Making them work, and work well, is relatively easy, and has been well
documented in many places, Apple, Windows and Linux etc...   So I wont
get into the whys and wherefores about password less boot ups etc...
(So easy to do, it's not even a stumbling block, and comments as to the
security of Windows passwords are entirely valid, they are way to easy
to get past.)

Making PC's electrically robust though, takes some "Imagineering",
especially in cars where the "Switched 12V" goes "Off" when you crank
the engine, and/or the main 12V dip's below about 9V when cranking (It
happens!) many micro ATX 12V input PSU's will "Burp" when under load
during those conditions, even if their spec says they wont....

You either need to take the ignition key from "Off" to "Start" in one
movement (fine for most petrol/gas engines, or diesels when warm)  Or
you need some "PC start delay" factor to prevent it booting the instant
it sees that sense line going live.  The thing then going back into the
power down state, just after it started to boot, when you have to pause
in the Ignition only state, before you actually start the engine (a cold
diesel with glow plugs and the associated timer etc)...   The result
*WILL* confuse Windows eventually, and Linux....

Of course, you could have a 12V UPS of sorts (also well documented) but
that adds complexity and hardware unless a second battery already exists
for some other purpose, or have a separate switch/button to
boot/shutdown the PC, also well documented, but there will always be the
one time where you mess up accidentally, & you *Need* the now confused
PC for whatever reason.  (Navigation typically)

About the best solution (but not the cheapest) that I personally have
come up with, is to use a full spec laptop, with it's own good battery,
and power that from the vehicle supply, with one of the easily found 12V
Laptop PSU's now available.   You only then need to remote the
screen/mouse/keyboard after that (and again, that has all been well
documented too) as the PC is designed to expect external power
fluctuations, automatically switching to internal battery when needed...
The only proviso, is that laptops need ventilation too, so stuffing it
down the seat pocket on the back of a passenger seat, does not work for

It also makes it very easy to remove the PC in a hurry if you need, and
also hide it well out of the sight too, especially if you only have one
power lead, and one USB lead, all I/O being done via a USB hub external
to the PC, even screen, rat and keyboard!

In many parts of the world, having things like cellular AirPort's, GPS
sensors, and mag-mounts visible on a car, would be a thief magnet in the
extreme.   Even if you cannot see any other "gadget" visible in the car,
they would still be more than tempted to brick a window and rummage
about quickly just in case they can find something....   Under the seats
is one of their first places they look, again from personal experience,
and car alarms are ignored these days sadly....

If you have a car you can modify, consider replacing the boot(trunk) lid
with a fibreglass version if available.  Then, you can have the GPS,
mobile data link etc hidden but available, while using the normal
broadcast antenna as a 2m 1/4 wave (with some clever duplexing/matching
etc)   If you can't do that, position cellular and GPS stuff, under the
rear parcel shelf, as that is often a light composite (RF transparent)
and has sight of the sky via the rear screen.

Lastly.   Make sure that when it's Off, it's well and truly "Off", or
you'll come back to a PC with a flat battery, and car with same. (Again,
personal experience...   The car's own security systems won't take
kindly to that sort of thing either...)  Also avoid DC/AC inverters, the
extra inefficiency really hurts if you need to use the PC kit without
the engine running, as many mobile gamers have found to their
embarrassment first time out...

Some car security systems also monitor the vehicle battery voltage when
the car is locked, any unexpected dips, will set the alarm off!  So
remote starting the data system, or APRS beacon power needs etc, could
be "a bit noisy"...

I suspect that the Acer EeePC would be a good mobile candidate for Ham
stuff, as it's relatively low power, and has no fragile hard-drive.  Yes
I know internal storage is a little tight, but you can add GB's of
external storage via USB.   They also supply a CD with all the needed
drivers for an XP install, should you not wish to use Linux, at least
they do here in the UK I am lead to believe from various websites.

Just my sixpence worth...

Dave G0WBX.
This mail has been scanned by Palmer Cook Computer Services Limited.  www.palmercook.co.uk

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