[aprssig] Tracker power control relay

[Scott Miller]

A ran a quick poll on the OpenTracker group, and it looks like the most
desired feature at the moment is support for a power relay.  This is
something I've been wanting myself - I've got a solar-powered weather
station to deploy, and with the radio on in receive mode all the time, it
puts far more load on the battery than necessary.

The TinyTrak3 has this capability already - I'm not sure what other trackers
might have implemented it.  I'm looking for input from anyone that's used
this sort of setup before on how it might be done best.  I'm not really
interested in controlling GPS power - I don't want to mess with the GPS
start-up delay - just driving a small relay to turn on and off the radio.
There will probably be a single setting to determine how long to apply power
before starting the transmission.

The OpenTracker has available output pins that'll provide up to 15 ma at 5
volts.  That's enough to run a small reed relay (with a snubber diode on the
coil to avoid inductive kick back) that'll power at least an HT.  I've been
thinking about including pads on the SMT version for a 2N7002 FET to drive
much larger relays if there's a demand for that.

I'm thinking about making a board with the power relay and a couple of
PCB-mounted APP connectors.  It'd fit in the same type of box as the tracker
itself, and would connect inline with it on the radio connector.  The radio
would plug in to the power control board, but power to the radio and the
output APP connector would be controlled by the relay.  I don't imagine I'd
be able to fit a large enough relay to handle anything bigger than an HT in
that enclosure, though.

Suggestions, anyone?  The first version will probably just be a config
setting that says 'turn on relay x msec before transmit', with a 5 volt, 15
ma output to drive the user-supplied relay.  If there's a need for anything
more elaborate, let me know and I'll try to design it with that in mind.

Scott
N1VG