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Chapter 2. Using TeleGPS Hardware
2.1. 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 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.
2.2. 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.
2.3. 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.
