[aprssig] OT1+ SMT telemetry

['Scott Miller']

Ok, I finally got a chance to implement the telemetry functions for the
OpenTracker+ SMT board.  It'll now give you 5 analog and 5 digital readings
in standard APRS telemetry format.  The supply voltage reading is still
shown in the status text, but not in the telemetry values with this
alternate firmware.

This should make the board a good replacement for the (apparently
discontinued?) MIM board, at around half the price.  If anyone really needs
a full 8 digital inputs, I can provide a tweak that'll do that at the
expense of the LED outputs.

I also did some testing with the on-board regulator and found that it does a
decent job of powering a 5-volt GPS receiver.  The Deluo SiRF III unit works
well since it draws at least 10 mA less than the older models.  You don't
want to run the supply voltage any higher than necessary, though - 12 volts
gets the regulator pretty warm, but 9 volts is much better.  The regulator
is in an SOT89 package so it can only handle so much heat dissipation.

The only difference in the firmware is in the selection of input pins.  All
of the regular OT1+ functions still work as usual, including tracking, NMEA
output, SmartBeaconing, and so on.

https://www.argentdata.com/catalog/product_info.php?products_id=64

The new through-hole boards are in, too - see
https://www.argentdata.com/catalog/images/ot1plus_kit.jpg.  Still v1.1 and
electrically the same as the previous batches, but these look cooler.  =]
They've got an immersion gold finish and black soldermask.  Oh, and I'm now
carrying ferrite filtered DB9's that'll work with the OT1+ and OT1m kits.
They're too expensive to make a standard part of the kit, but they ought to
provide an extra bit of RFI protection.

Scott
N1VG