[aprssig] New Truck/Setup Ford Expedition GPS and Install Questions

Stephen H. Smith wa8lmf2 at aol.com
Mon Feb 4 00:44:03 CST 2008

Scott Miller wrote:
>> What's the chance once you get this going,  of a spinoff device that 
>> would replace the TX/RX audio in/out of the T2 with a serial port?
>> I'm thinking of what would essentially be a protocol converter that 
>> could go inline between an existing D710/D700/TH-D7 or a KPC3 and the 
>> Nuvi, allowing the Nuvi to act as an intelligent terminal for 
>> existing TNCs.   I'm thinking that the existing board layout could be 
>> re-used with the on-board radio-interface DB9 connector re-purposed 
>> to be a RS-232 serial interface instead.     Or does the CPU only 
>> have one hardware serial port?
> Do any of those do APRS in KISS mode?  Or would it have to deal with 
> converse mode?

Yes they do KISS mode, but I was actually thinking of the Nuvi being 
connected to the dedicated GPS port of the radio.  

The converter would construct standard NMEA format strings from the 
Garmin binary data to send TO the Kenwood, and receive/display waypoints 
based on received stations sent FROM the Kenwood while the radio 
functions in stand-alone APRS mode. 

Of course this would sacrifice the messaging capability.  However it 
would duplicate the functionality of the AVmap5/Kenwood combo using your 
choice of less expensive Garmin GPS units.    [The AVmap interfaces to 
the Kenwoods via the bi-directional GPS port on the radios.]

> Hardware-wise, it's certainly doable.  There are already two serial 
> ports present on the data side DB9 - I've got 'Y' splitter cables 
> being made now.  Or, as you suggest, the same case layout could be 
> kept with a different board.
> I don't relish the idea of dealing with the D7xx user interface and 
> all of the quirks and differences in the radios, but it could 
> certainly be done.  Things like message queue handling might get 
> interesting, with two different messages sources and sinks.
> Speaking of message queueing, I've got that working on the Nuvi.  You 
> can enter as many messages as you can fit in the Nuvi's queue, and 
> they'll show 'sending' until an ACK is received from the remote 
> station, at which time the message shows the delivery timestamp and it 
> moves on to the next one.  If you want to kill the current message, 
> you just click 'delete' and in a few seconds the T2 goes on to the 
> next one.
> The fleet management interface also provides a mechanism for simple 
> 'OK' acknowledgments, and also for YES/NO responses.  I'm not sure how 
> this might be used in APRS, but it's certainly worth checking out.  
> Maybe a special flag could be used in APRS messages to indicate that 
> they can accept a simple (manual!) acknowledgment or YES/NO, with the 
> response returned in a standard format.
> You could use this, for example, to send a 'return to base' message to 
> a whole group of vehicles, and they could all indicate receipt with a 
> single button push.  No need to manually key in a message, and the 
> sender can be sure that someone actually saw the message.

This is sounding more and more like a commercial land-mobile 
status-reporting terminal of the type used by taxis, utilities and fire 
departments.   These non-computer-based devices usually have half a 
dozen buttons for canned fixed messages like "Out of Service", "Enroute 
to Call", "Arrived at Destination", etc.  Of course, I assume that 
that's what Garmin had in mind with their "Fleet Management Interface" 
-- AVL combined with simple messaging and status reporting, using the 
GPS device as the terminal.


Stephen H. Smith    wa8lmf (at) aol.com
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