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[aprssig] Radio/GPS power control

Scott Miller scott at opentrac.org
Fri Jul 23 17:17:29 UTC 2004


> How does it handle channel-busy situations? My empirical evidence from the
> TT3 was that if it turned on the relay and the channel was busy for n
> seconds, where n>~5, it would keep the relay on, but not transmit when the

At the moment, the algorithm is very simple.  Once a transmission is pending
(due to beacon timer, smartbeacon cornering, profile switch, external
trigger, etc) it turns on the relay and starts another timer.  It transmits
once that timer expires, it's got a valid GPS position, and the channel is
clear.  It'll keep the relay on until the channel is clear.  At the moment,
it'll also stay on if it loses GPS lock.  I'm considering adding another
timer for channel busy timeout.  I'm worried that if you've got, for
example, a solar powered weather station that starts getting some RFI, it'll
run the batteries down.

> Does the OT keep the relay on until it finally get the posit out? Does the
> OT keep updating the position packet to the latest position/speed while
the
> channel is busy (the TT does)?

Yep.  Which means you might get an extra bit of delay if it's receiving a
new position when the relay timer is up.

> While perhaps harder to kit, a good strain relief is very important. I
find
> that a cheap way is to solder your cables as normal, and then drill two
> holes in the PCB and use a 4" zip-tie to cinch the cables down to the PCB.
> Two zip-ties in a row is even better.

That's an idea.  I'm personally a fan of filling the entire enclosure with
hot-melt glue, but that makes rework difficult. =]

Scott
N1VG





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