[aprssig] APRS in-dash display

Andrew P. andrewemt at hotmail.com
Sun Jan 17 14:25:14 EST 2016

>Subject : [aprssig] APRS in-dash display
>From: Lee Bengston
>Date: Sun Jan 17 11:25:02 CST 2016


>On Jan 17, 2016 12:24 AM, "Greg D via aprssig" <aprssig at tapr.org<http://www.tapr.org/mailman/listinfo/aprssig>> wrote:

>> Hi folks,

>> Picking up on a thread I started a while back... Not sure if this will

>> lead to something permanent or not, but I tought I'd give it a try.


>> I got access to the back of my car's in-dash unit, and the video

>> input connector. It's meant for use with a back camera, which I

>> currently don't have (though it's on the wish list...). Found a VGA

>> to RCA adapter box, and fired up APRSIS32 which was loaded

>> on a small laptop. Here's the result:

>> http://home.wavecable.com/~ko6th/aprs_dash_display.jpg<http://home.wavecable.com/%7Eko6th/aprs_dash_display.jpg>

>> http://home.wavecable.com/~ko6th/aprs_laptop.jpg<http://home.wavecable.com/%7Eko6th/aprs_laptop.jpg>


>> Given the difficulty, if not questionable legality, of controlling a GUI-based

>> laptop while driving, I think the next steps need to include:


>> 1. Replace the laptop and VGA adapter with a Raspberry Pi. VGA output

>> is built-in, also much better power draw and small size. (The car is a sports

>> car, so no room for anything bigger.)

> I think you meant RCA is built in, right?


>> 2. Replace APRSIS32 with YAAC (for Raspberry Pi compatiblity).


>> 3. Probably still need a keyboard for full control while parked, but add some

>> fixed key switches tied to keyboard shortcuts for the common stuff while driving.

>> During the earlier exchange, Andrew figured it was a "simple" matter of a Java

>> library to bridge the swtiches to keyboard shortcuts... Hope he's right.


>> 4. The Pi will boot itself when the car turns on, but I need a way to

>> automatically safely power down the Pi when I turn the car off. Any ideas on this?

> A lot of vehicles don't shut the radio off immediately - will eventually time out - and

> many will shut off once you open the door. You could source the power from a

> source that doesn't shut off right away and buy yourself time to shut down gracefully.

>Sounds like fun - my truck has a backup camera that I would not want to be without. :-)

>Lee - K5DAT

This is a project I've been fiddling with for a couple years, since I acquired a motor home. However, after a couple years of driving "the moose", I don't think I want to give up the backup camera video monitor, because:

1. The monitor is tiny and black and white (the motor home is an old 2005 model and actually has a 6" CRT monitor, not a LCD/LED one).

2. Driving a vehicle that large and awkward with all the lunatics on the highway, I want all the views I can get of overtaking maniacs so I can be ready for them.

However, I could defeat the ignition power interlock for the main TV set (above the windshield) and hook a Pi onto that larger monitor (and I've been looking at replacing that old  CRT TV with a flat-screen 12v set anyway), so I could have the Pi view up there.

The Pi4j library (http://pi4j.com/) provides Java-language access to the GPIO pins on the Pi, including supporting I2C; as an exercise for the student, I wrote a non-published plugin for YAAC (based on the provided sample plugin) that would copy the text of incoming messages to one of those 16x2 LCD displays that connect to the GPIO pins. Using the same library, you could have YAAC listen to button pushes on one of the Pi daughterboards that provides user input (the LCD module I had also had a few buttons on it, but in places mechanically awkward to put in a project box), and convert a button push into the equivalent of clicking on a menu entry (by calling the actionPerformed() function on the desired menu entry or GUI widget, such as the zoom in or zoom out buttons).

Regarding power, I have already had to replace the CD-eating broadcast-band radio in the motor home's dashboard anyway, so I know I have multiple power source wires in the dashboard, some direct from the engine starting battery, some ignition-switched, and some from the coach (RV appliance) battery bank. Not sure what kind of "safe" you need for powering down the Pi; I usually just pull its power cord, although I suppose it should have a proper power cycle and "poweroff" command for flushing disk caches from writing the YAAC log files; you could figure that out with a GPIO pin connected to switched power (through an appropriate voltage divider so you don't fry the Pi), and using one of those timed poweroff devices that are sold to protect your battery from being overdrained by your ham radio rig when the ignition is off (just make sure the time is longer than the interval needed for the Pi to shut down) to feed the power to a 12v-to-5v converter for the Pi.

I have found a few tiny (approx. 6" long) Bluetooth keyboard/mouse gadgets that work well with the Pi over the WiPi USB plugin, so you could shove said keyboard in the door pouch and pull it out when needed (i.e., when parked).

I've mostly been delayed on this project by trying to figure out how to wire an anemometer on the roof of the RV without putting more leaks in the roof, having the anemometer destroyed by the first low-hanging tree branch I pass, or wrecking the interior trim trying to get the anemometer wiring back to the Pi at the dashboard.

I strongly recommend using the Pi 2 for this project, as YAAC is not a very fast renderer of streets on a Pi (despite all the effort I've put into making the street renderer faster); you'll need all the CPU power you can get.

Just my $.02.

Andrew, KA2DDO

author of YAAC
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