Cambridge GPSNAV Connection

Initial Cambridge GPSNAV Support

The following data transfer/information is supported:

  • The GPSNAV output can be used to drive SoaringPilot completely and correctly. I have confirmed this definitively. However, to make this work correctly and make it so that you don’t have change cables to send info to the GPSNAV, SoaringPilot EXPECTS to be connected to the port on the GPSNAV marked “Data Port (DCE)”. It is the one with the DB9 plug. You cannot use the port marked “Datacom (NMEA-0183)”. That port ONLY outputs basic NMEA data and allows no two-way interaction. You can see a diagram describing the pins for this connector at the bottom of this page. To get the PDA power, you must have a GPSNAV that has or has been upgraded to Version 6.0 or beyond. Note that the GPSNAV only outputs at 500 mAmps or 0.5 Amps. If your PDA is fully charged, this should be sufficient to power it properly. If the PDA is not charged, it may need more power than this to charge and power the device.
  • For proper operation, SoaringPilot should be connected to the running GPSNAV BEFORE starting the program. If configured for the GPSNAV as the “Comp” on the NMEA/Port screen, when SoaringPilot starts, it sends the NMEA command to the GPSNAV that makes it begin sending NMEA data. The NMEA mode of the GPSNAV sends the NMEA GGA lines including the GPS altitude. It also outputs the GSA and GLL lines which properly drive the GPS Info screen if you have the latest/version 6.0 of the GPSNAV firmware installed..
  • This version DOES NOT use the pressure altitude value from the GPSNAV yet. It turns out that in order to make the GPSNAV output the Cambridge pressure altitude sentence, the unit must be “activated”. I have been working with Chip Garner and he is supposed to send me the code to do this. So I’m hoping to add this soon. However, since it does output GPS altitude, the additional pressure altitude may not make that much difference.
  • Waypoint Transfer To the GPSNAV - You can transfer waypoints from the SoaringPilot to the GPSNAV. This can be done from the “Transfers” screen. In addition, when you declare a Task to the GPSNAV, the turnpoints are transferred to the GPSNAV first before the task is declared. Because of the way the GPSNAV task declarations work, this is required. The GPSNAV task declaration is simply the waypoint number for each of the turnpoints. So if the turnpoint numbers in the GPSNAV don’t match those in SP then the declaration will not be correct. There are a couple of additional caveats to the waypoint transfer as well. First, when the transfer is done in either case, the waypoint database is first sorted into Ascending (0-9,A-Z) alphabetical order. Then the waypoints are transferred. Second, the GPSNAV can only hold a maximum of 250 waypoints. Thus, after they are sorted, only a maximum of the first 250 turnpoints are sent if there are more than that in the SP waypoints database. So if you want to ensure that your turnpoints get into the GPSNAV either have less than 250 or put numbers in front of the names to force them to the top of the list.
  • Task Declaration - As with the other Logger types, when you activate a task, you will be asked if you want to declare it to the GPSNAV. If you answer yes, the waypoints will be transferred and then the task will be declare into the GPSNAV.
  • Configuration Transfer to the GPSNAV - From the Transfer screen, you can select either “Glider” or “Pilot” from the drop down list and it actually does the same thing. These items are not separate in the GPSNAV as they are in the 302. They are transferred into the GPSNAV with the same command. The Glider info is the Glider Type and Contest ID. The Pilot Info is the pilot name. In addition, the Units are also transferred along with the other info. On the “Logger Data” screen off of the “Logger Config” screen, in addition to the Arrival and Approach radius values, there is a checkbox. If this is checked, the config info will also be sent when a task is Declared. This is an option but is highly recommended.
  • There is one caveat to the units transfer. The GPSNAV supports 4 units setting groups for Distance, Height and Vertical Speed. These groups are Nautical miles, feet, knots or Kilometers, meters, meters/sec or Kilometers, feet, knots or Statute miles, feet, knots. So to accomodate this, the following rules are used for determining what units from SP to transfer into the GPSNAV If distance is set to NM, set the GPSNAV to Nautical miles, feet, knots. If distance is set to KM, check the altitude setting. Based on that set to either Kilometers, meters, meters/sec or Kilometers, feet, knots. If distance is set to SM , set the GPSNAV to Statute miles, feet, knots.
  • There are other miscellaneous functions which can be done through the Transfer’s screen. You can delete all of the flights in the GPSNAV. You can also delete all of the Turnpoints out of the GPSNAV. However, be aware that when you remove the turnpoints, it also deletes any task declaration and the Pilot Name. Since those get put back in at task declaration time, that’s really not that big of an issue.
  • I hope the above is acceptable to everyone. It’s about the best that can be done with the limitations of the GPSNAV. The only items left that I want to add for the GPSNAV support are being able to activate the GPSNAV so that the pressure altitude is outputted and to be able to download flight logs from the GPSNAV. The flight transfer option is active in this version but it doesn’t really do anything yet. Again, I am waiting on some additional technical information I’m waiting to get from Cambridge, Chip Garner and/or Guy Byers. Hopefully soon.

Can the GPSNAV Provide Power To A PDA?

Technically, the answer to this is yes. As the diagram below shows, the GPSNAV with the latest update can supply 5 volts to a PDA. However, this is only 500mA. This should be fine if you start with a full or nearly fully charged PDA. However, if you attach a PDA that needs to be charged, some PDA‘s can draw more than 500mA. The 302 for instance outputs at 1 Amp. This is just something you want to keep in mind.

Is the GPSNAV Display Required To Work With SoarPilot?

No, SP doesn’t require the GPSNAV display at all. In fact, I’ve found that when you change some info on the GPSNAV using their protocol, the changes don’t always show up on the GPSNAV display unless it is restarted. This seems that it could cause some confusion if using both.

Is it better to put waypoints and tasks in the GPS NAV or SoarPilot?

The way it’s implemented in SP, the waypoints (first 250 sorted alphabetically) will be sent to the GPSNAV. This required for the task declaration with the GPSNAV to work properly. Basically, SP treats the GPSNAV as just a source of positional info and then sends the GPSNAV what it needs to do proper logging and task declaration.


soarpilot/cambridge_gpsnav_connection.txt · Last modified: 2006/10/25 11:24
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