Avionics Communications questions

[ShawnR]

My project is a simple one, relative to the panels I see being built here. But, I have some questions about the components "communicating".
I have an EDM350 engine monitor that can receive data from the Aera660 GPS to display fuel data. The EDM manual just says to connect the RS232 data lines to the GPS but does not specify a protocol. The AV30's can use NMEA as does the GPS so will I assume the engine monitor will use that protocol as well?

For physical connections, I have been looking but cannot find info on that directly. A friend has a Garmin manual and it kind of shows that to make 2 connections to one pin in a DSub connector, I can just solder a connection onto the pin wire, a little back from the pin, and then cover in heat shrink? Since my 15 pin dsubs don't use many wires, they should accommodate such a connection. Or is there another method for doing these connections? I would think I need to maintain shielding, so guessing it needs to be contained within the dsub housing? Or am I worrying too much about the short piece of exposed unshielded wire on a data line? Attached is my wiring diagram, still in development....

Any input/critique/suggestions appreciated. Thanks.

 

[1bigdog]

Hi Shawn

generally RS232 implies a serial protocol meaning the EDM instructions should provide guidance on baud rate, stop bits, and the like. The most common implementation would probably 9600, 8, none and 1. But their documentation says use the GPS provider for the connection guidance. That said I think your diagram suggests an input to a GPS type input. Thats not going to work. Its simply sending serial telemetry from you engine and its assumed your display will have the facilities to present the engine telemetry.
review the 660 manual for how they take in a serial input, how the serial port is configured and how the data gets displayed. And/or contact JPI and ask for some better guidance.
Good luck.

 

[ShawnR]

Thanks Michael

Here are the excerpts from the manuals. And some info from JPI for the EDM350. I asked them if I should connect the engine monitor to the GPS as my searches on line only referred to other models. His reply stated the EDM350 will use data from the GPS. I think it is only one way, ie, into the engine monitor. So yes, reading your text, the GPS will not display any engine data, just the other way. I can contact him again but here was his reply to my last question....

JPI email
Hello Shawn,
Yes, it is beneficial to connect the two RS 232 wires (in and out) on the EDM 350 to your GPS. When the two instruments are connected and exchanging information, ours can display ‘REQ’ which is fuel required to either destination or next waypoint (selectable). It will also display how much fuel you can expect to have at destination (or waypoint) ‘RES’ at the current fuel burn rate.
.....
JP Instruments, Inc.

Garmin 660 manual
Overview
GENERAL INTERFACE SETUP
The Interface Setup controls the input/output format used when connecting the unit
to external devices.
Selecting an interface:
1) From the Main Menu, touch Tools > Setup > Interface.
2) Touch Serial Port 1 or Serial Port 2.
3) Touch Serial Data Format. A vertical list is displayed.
4) Touch the desired data format ('Garmin Data Transfer', 'NMEA Out',
'Aviation In', 'Aviation In/NMEA & VHF Out', 'GTX TIS-A In', 'GTX
TIS-A In/NMEA & VHF Out', 'Garmin Data Transfer', 'MapMX', or
'None'.
Restoring interface defaults:
From the Main Menu, touch Tools > Setup > Interface > Menu >
Restore Default.
Serial Data Formats
• None: Provides no interfacing capabilities.
• NMEA Out: Transmits NMEA position, velocity, and navigation data.......

EDM350 Manual
20. GPS Interface
Use the P4 connector harness 700708 labeled RS232 OUT TO GPS (white) and RS232 IN FROM GPS (gray).
Refer to the Manufactures GPS manual for the required pin connections on the GPS.

uAvionix AV30 Manual
GPS Interface (Optional)
The GPS interface is an optional RS-232 serial input that is compatible with the industry standard “Moving Map” output provided by most panel mounted GPS units, and NMEA serial interfaces provided by most hand-held GPS units.
This is a text/binary protocol output by the GPS navigator that contains situational awareness information such as ground speed, track, distance to destination, cross track, etc, and is typically utilized by remote mapping/display products to provide additional pilot awareness.
This output does not provide IFR compliant lateral or vertical guidance, therefore all deviation related data presented is for VFR operations only.
The AV-30-E does no computations or operations on the data obtained from the GPS navigator, and simply displays the received data in a textual or graphical format as configured by the pilot.
UAV-1004234-001, AV-30-E, Installation Manual 18 Revision B
This serial interface may be connected in parallel between multiple AV-30 units and is supported in both the AI and DG modes.
The supported protocols are contained in Section 11- Serial Interface Specification.

 

[GalinHdz]

After you have properly connected them together, set your GPS to "NMEA OUT" and see if it works. If you need the GPS data at the EDM350 and other pieces of equipment, then set the GPS to "Aviation In/NMEA & VHF Out". "MOST" modern equipment can communicate with the NMEA protocol so that is your best bet.

If that doesn't work then contact JPI for specific help.

 

[Majorpayne317641]

RS232 does need shielding. Whatever wire you are connecting and splicing into must be shielded. You should leave no more than about 1.5in exposed from the solder shoulder that then connects to the backshell with a ground wire. Each manufacturer has different instructions but that’s the basics. If you have a Garmin manual it should explain wiring techniques in its own section.

 

[ShawnR]

After you have properly connected them together, set your GPS to "NMEA OUT" and see if it works. If you need the GPS data at the EDM350 and other pieces of equipment, then set the GPS to "Aviation In/NMEA & VHF Out". "MOST" modern equipment can communicate with the NMEA protocol so that is your best bet.

If that doesn't work then contact JPI for specific help.

Thanks. I sent off an email earlier this morning to JPI asking for clarification again, as suggested. I also sent them my proposed diagram. I will report back.

 

[ShawnR]

RS232 does need shielding. Whatever wire you are connecting and splicing into must be shielded. You should leave no more than about 1.5in exposed from the solder shoulder that then connects to the backshell with a ground wire. Each manufacturer has different instructions but that’s the basics. If you have a Garmin manual it should explain wiring techniques in its own section.

Thanks. I only have the Aera660 manual (limited info as it is a portable) but can take a look at a friends again. Perhaps I can find one online. I have not pursued the Garmin connection methods directly yet.

Edit...that did not take long.....

I should be able to find my answers here.

 

[uk_figs]

You can daisy chain the RS232 from the aera 660 to up to 5 devices, the "Aviation In/NMEA & VHF Out" is the most common selection as noted in the thread. One thing to note is that the AV-30 will only display nautical miles in the "distance to waypoint" field even if you have miles per hour and statute miles selected as part of the setup, something to do with the NMEA output of the portable (at least this is how it works on the aera 760).
Figs