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== Using TeleGPS Hardware
=== Hooking Up Lithium Polymer Batteries
TeleGPS has a two pin JST PH series connector to connect up
a single-cell Lithium Polymer cell (3.7V nominal). You can
purchase matching batteries from the Altus Metrum store, or
other vendors, or you can make your own. Pin 1 of the
connector is positive, pin 2 is negative. Spark Fun sells a
cable with the connector attached, which they call a
link:https://www.sparkfun.com/products/9914[JST Jumper 2 Wire Assembly]
[WARNING]
Many RC vendors also sell lithium polymer batteries with
this same connector. All that we have found use the opposite
polarity, and if you use them that way, you will damage or
destroy TeleGPS.
=== On-board Data Recording
TeleGPS logs GPS data at a user-configurable
rate. Data are logged to a 2MB on-board flash memory
part, which can be partitioned into several
equal-sized blocks, one for each flight. 64kB of this
storage are reserved to hold configuration data,
leaving 1984kB for flight data.
The on-board flash is partitioned into separate flight
logs, each of a fixed maximum size. Increase the
maximum size of each log and you reduce the number of
flights that can be stored. Decrease the size and you
can store more flights.
To compute the amount of space needed for a single
log, you can divide the expected time (in seconds) by
the sample period (by default, 1 second per sample)
and then multiply the result by 32 bytes per
sample. For instance, a sample period of 1 second and
a flight lasting one hour will take 32 * 3600 = 115200
bytes. TeleGPS does try to reduce log space used by
not recording position information when it isn't
moving, so actual space consumed may be less than
this.
The default size allows for four flights of 496kB
each, which provides over four hours of logging at 1
sample per second.
TeleGPS will not overwrite existing flight data, so be
sure to download flight data and erase it from the
onboard flash before it fills up. TeleGPS will still
report telemetry even if memory is full, so the only
thing you will lose is the on-board data log.
=== Installation
The battery connectors are a standard 2-pin JST
connector and match batteries sold by Spark Fun. These
batteries are single-cell Lithium Polymer batteries
that nominally provide 3.7 volts. Other vendors sell
similar batteries for RC aircraft using mating
connectors, however the polarity for those is
generally reversed from the batteries used by Altus
Metrum products. In particular, the Tenergy batteries
supplied for use in Featherweight flight computers are
not compatible with Altus Metrum flight computers or
battery chargers.
[WARNING]
Check polarity and voltage before connecting any
battery not purchased from Altus Metrum or Spark
Fun.
TeleGPS uses an integrate GPS patch antenna and won't
receive GPS signals if installed inside a metal or
carbon fiber compartment. Test GPS reception and
telemetry transmission with the system installed and
all other electronics powered up to verify signal
reception and make sure there isn't any interference
from other systems.
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