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

Scott Miller scott at opentrac.org
Mon Feb 4 06:28:22 UTC 2008

> 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?

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.


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