[aprssig] Car radio APRS display?

KF4LVZ aprssigZbr6 at acarver.net
Mon May 18 02:58:10 EDT 2015

On 2015-05-17 21:17, Stephen H. Smith via aprssig wrote:
> On 5/17/2015 11:05 PM, Greg D via aprssig wrote:
>> Hi folks,
>> I recently acquired a new (to me) car, which has a Audio / Nav / etc.
>> display
>> unit in the dash.  The port for the backup camera is unused (no camera
>> installed), so I was thinking it would make an interesting place to
>> push an
>> APRS map.  Baseband video is all that's required.  According to the
>> manual, the
>> reverse gear interlock can be disabled, so I should be able to select
>> it when
>> in motion.
>> I was thinking the original Raspbery Pi might make for a good computer
>> to drive
>> it, as it is small, runs a full Linux graphical OS, has a built-in
>> video out,
>> and runs on minimal power.  But, what software to run, and how to
>> control it
>> without a QWERTY keyboard and/or mouse? There is no room on the dash
>> or nearby
>> to host a laptop or tablet or such, and none of the existing software
>> I know of
>> is car-friendly (thinking driver distractions).
>> What I really need is something that just comes up with a map and moving
>> icons.  Maybe a button or two for zoom in/out, one for a list of
>> stations /
>> messages heard, something simple for sending predefined messages
>> back.  I'd use
>> one of the small receive-capable "Tracker" sorts of units to provide
>> the raw
>> data (RF + TNC).  I don't think any of the existing "Ham HUD" sorts of
>> units
>> have internal maps and video out, but that would be even ideal.
> 1)    The backup camera inputs are normally classic ANALOG 640x480
> composite NTSC (the former US broadcast standard now used by virtually
> nothing except CCTV cameras).   I.e. resolution equivalent to old-time
> analog TVs or early PC CGA video output, and not remotely high enough
> for today's GUI computer interfaces.
> 2)    The video-out on an unadorned Raspberry Pi is HDMI DIGITAL
> compatible with the majority of today's flat-panel monitors and digital
> TVs. The resolution is typically either 1344x720 or 1920x1080. I.e.
> equivalent to today's digital HDTVs.

The Raspberry Pi's (A, B, and B-plus) all have analog video out
available via the audio/video jack (a four-conductor TRRS jack).  The
output format is standard NTSC suitable for any NTSC monitor so it would
work just fine on the in-dash display.


The HDMI port resolution is adjustable via the configuration file in the
root directory of the Pi.  You are not limited to the high resolution
formats.  I have a Pi set to a much lower resolution driving an older
VGA monitor.  It works fine.

As for resolution in NTSC, the output is suitable for viewing rough
icons on a modest map.  Lines marking highways and major roads would be
fully viewable.  Small fonts may not show up very well but larger fonts
would be readable.  Icons would need to be large enough to see or
distinct enough to tell them apart (solid colors, basic outlines).  The
NTSC output of a Raspi is actually respectable so using one on the rear
view camera input is possible with reasonable results.

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