[aprssig] Balloon - lessons learned (AVMAP-GPS) - GreenLight Labs GPS?

[Randy Love]

For the cost of a AVMAPS, you could have run a nice netbook or tablet with
preloaded OSM maps and APRSIS32, letting the GLL GPS feed location
information to the 710 while the APRSIS32 gathered data directly from the
710 TNC port on the back of the 710 head, including your location via GPS
passthru from the TNC.

I do this for MS-150 bike events in a SAG vehicle. If I want street-level
point-to-point navigation, I use a separate Nuvi 350 for that. My APRS
overview is actually a Win7 tablet running APRSIS32 feed RF data from the
710.

Running two GPS's like that seems overcomplicated to me.

Anyway, I'd never expect my 710's ( I have 2 of them ) to operate properly
if there were two possibly conflicting GPS sources vying for the same data
port.

That's me and my experiences.

Randy
WF5X


On Mon, Apr 7, 2014 at 5:22 PM, Stephen H. Smith <wa8lmf2 at aol.com> wrote:

> On 4/7/2014 12:24 PM, Robert Bruninga wrote:
>
>> For the chase, we added an AVMAP GPS for the map display and plugged it
>> into
>> the "pass-through" socket on the Green light labs GPS.  Everything seemed
>> to be
>> working.
>>
>> 20/20 HINDSIGHT HINTS:  Occasionally we notice the D710 was not updating
>> and so
>> we cycled power and continued.  Some times the AVMAP was not updating.
>> Sometimes when the AVMAP was plugged into the Green Light Labs GPS, then
>> the
>> D710 did not get GPS updates. But generally, a power cycle fixed it.  Did
>> it
>> maybe 3 times during the all day chase.
>>
>>
> What kind of a kludge was this????       What does the "pass-through" port
> on the Greenlight actually do?  Is is routed through some sort of
> uController that can buffer and arbitrate data flow through the main port?
> (The way GPS passthrough is handled on the Kenwood radios?)
>
> Or is it just a second jack physically wired in parallel with the main
> output, intended to strictly provide GPS data to a second receiver-ONLY
> such as a laptop running a mapping program, hooked up with a one-way
> two-wire connection?
>
> The AVmap talks as well as listens, since it acts as THE GPS source, as
> well as a data receiver for mapping, when connected to a Kenwood radio's
> GPS port.
>
> With TWO RS-232 devices,you have a simple cross-over "null modem" with TXD
> on each going to the RXD side on the other.   But how do you connect
> *THREE* RS-232 devices, each with an active output to each other
> simultaneously?
>
> Presumably the Greenlight's TXD (active TTL or CMOS output) was going to
> the D710's RXD pin.  But so was the AVmap's TXD (GPS data out).  So now you
> have the AVmap -AND- the Greenlight trying randomly to talk to the Kenwood
> at the same time.
>
> With THREE RS-232 talkers and TWO RS-232 listeners sharing a single set of
> wires, with no polling or time-slotting, it's a virtual certainty that
> RS-232 transmissions from more than one device at a time would overlap, and
> further, create "tri-level" RS-232 (high, low and somewhere in-between)
> when a bit was HI on one sending device and LO on another.
>
> In turn, it's no surprise that one or more of the receiving CPUs involved
> would choke and lockup when this kind of unparse-able trash was fed into
> them!
>
>
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