Author Topic: Shared Data Between CN and CNv  (Read 642 times)

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cemx86

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Shared Data Between CN and CNv
« on: January 04, 2021, 04:01:20 PM »
I have a CNII and a CNv.  They each have a GPS antenna.  They are also connected to one another though they are considered standalone avionics. 

I'm not exactly sure what data that they share with one another through the CAN bus.  Wind?  [As an aside I have a Cambridge 302 also connected to the CNII - what sharing goes on there?]

My question is, shouldn't/couldn't they share GPS data?  That is if one GPS system (antenna or receiver) conks out then the other takes over for both of the pieces of equipment.  Better yet I could get rid of one [two] GPS antenna.  I will shortly be up to 5 of them when I install ADS-B. 

- John
Thanks, John OHM Ω

Evan Ludeman / T8

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Re: Shared Data Between CN and CNv
« Reply #1 on: January 06, 2021, 11:15:35 AM »
Secure flight recorder issues at play here.

There are a few threads on this board that deal with GPS signal splitting.  Haven't tried it myself, but several users have made it work.

Communication between CNv and CN2 is via serial bus.  IIRC all CN2 uses at this time is wind. 
Evan Ludeman / T8

cemx86

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Re: Shared Data Between CN and CNv
« Reply #2 on: January 06, 2021, 07:55:53 PM »
About using a GPS splitter (often called a combiner which I don't quite understand) - I am conflicted. 

If I use such a device to go from four (soon to be 5) GPS antennas down to one, which is powered by a single avionics device, then I loose all the redundancy I currently have.  One device dies and every device looses GPS. 

So I prefer a SeeYou Mobile Oudie GPS schema of redundancy.   The Oudie (I and II, unsure about the IGC) has an internal GPS.  If you connect another device with a GPS, e.g. a Cambridge 302, the Oudie will work with either GPS (defined as primary or secondary).  If one GPS signal is lost, then the other takes over.  Smooth.  Seamless. 

It seems that the various manufacturers of avionics that use GPS (seems that nearly all do these days) simple don't want to create a working group to agree to a single communications protocol between all devices.  I know of many examples through the years where manufacturers of a given technology each choose a proprietary way to implement a function for seemingly for self-serving reasons. 

A simple example we can all relate to is the earlier days of cell phones where every manufacturer, and sometimes the same manufacturer, had different charging cables for each phone.  Buy a new phone and you had to throw away all your chargers and start over again.  Slowly this condensed to MiniUSB, MicroUSB, and Lightning.  Now it seems that USB-C has become *THE* standard.  Heck, even Apple has seen the light.  Hurrah!  Are you old enough to remember the early days of computer inter-connectivity where there was a witches caldron of choices to deal with.  Now we simply EXPECT the ease of plug and play computer connectivity. 

FLARM has shown the wisdom of a standard communications protocol.  Many (all???) new soaring avionics have jumped on the FLARM plug and play bandwagon.  This has allowed this key safety tool to be implemented and to grow exponentially for the benefit of all.  Hurrah again! 

Why can't GPS follow this same path? 

Thanks, John OHM

<<<Hey, that was pretty good. I should send that to Soaring magazine!>>>

Thanks, John OHM Ω

carbonprop

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Re: Shared Data Between CN and CNv
« Reply #3 on: January 07, 2021, 06:39:38 AM »
If you enter a ballast amount into CNII it copies to CNv.  If you enter or change MC on CNII it also changes on CNv. If you enter those things on CNv they are not copied to CNII.  Also, CNv and CNII use different ballast schemes.

Evan Ludeman / T8

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Re: Shared Data Between CN and CNv
« Reply #4 on: January 07, 2021, 04:14:09 PM »
The communication protocol isn't the issue. 

You can't use an incoming data stream in a secure flight recorder (for fairly obvious reasons).
Evan Ludeman / T8

Evan Ludeman / T8

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Re: Shared Data Between CN and CNv
« Reply #5 on: January 07, 2021, 04:15:18 PM »
If you enter a ballast amount into CNII it copies to CNv.  If you enter or change MC on CNII it also changes on CNv. If you enter those things on CNv they are not copied to CNII.  Also, CNv and CNII use different ballast schemes.

True.
Evan Ludeman / T8