• General Aviation GPS Hardware Interface

    Tutorial Presented By Member Steve Masters (Steve1970)
    Steve Masters, explains on how to make your own general aviation GPS system interface "GarSim GNS530" and also work with Reality XP Software Guage and Microsoft FSX.


    Design Scope and basics

    Design Details
    • Software Used
    • Screen Shots
    • Overall Dimensions / connections

    Component Parts
    • LCD Screen
    • BU0836X Interface Card from Leo Bodnar
    • Custom made PCB
    • Buttons and Encoders
    • Custom Face plate
    • Lettering
    • Enclosure

    • Reality XP GNS530 Gauge for FSX
    • Modifying the Gauge file to show the border only
    • Modifying the RXP.INI file for key assignments
    • FSUIPC
    • Input Assignments

    Recommended Suppliers / Parts list / costs

    Links to downloads

    Design Scope
    As a real world general aviation pilot, I often hire aircraft equipped with the Garmin GNS satellite navigation system. The use of these systems in general aviation is now widespread although the baby brother Garmin GNS430 is most popular, especially in the smaller aircraft such as the Piper PA-28.

    The GNS530 is a larger unit but the functionality between the two is very similar and if you are comfortable and familiar with using the 430, then the 530 will be easy to use and vice versa.

    In real world aviation the GPS should only be used as a backup navigation device, and a good GA pilot will always have a printed PLOG or pilots log to use during the flight in conjunction with an up to date chart of the area in which he/she is flying. For most GA pilots, dead reckoning and flying under visual flight rules should be maintained at all times with reference to landmarks, roads, towns and other prominent features of the landscape. That said the GPS system offers the pilot a great tool with which to aid in navigation and to avoid infringing controlled airspace, which in the UK is particularly dense.

    In setting out to improve my overall level of realism in using FSX I was looking for a method to replicate the Garmin I use real world. There are currently no commercially available products with compatibility to FSX available on the market, so I decided to have a go at building my own. There are several examples of similar projects on various Internet sites from which I have learnt. www.mycockpit.org is also a very useful place to visit with a very active forum of members.

    In practice this project is very simple to undertake, here are the basic fundamentals on how it all works.

    • All buttons and encoders on the GarSim530 hardware are wired to the BU0836X Interface card.
    • The BU0836X USB Interface card is recognized by windows as a USB controller (no drivers required)
    • Each button press/encoder pulse is interpreted as a button number (under game controllers)
    • The button numbers are mapped in FSUIPC to key press combinations (e.g. win+F2)
    • The key combinations are defined in the RXP.ini file to perform the necessary actions (e.g. press VNAV)

    Software Used
    Approximately 150 design hours have been spent in completion of the GarSim530 basic design.

    The software used was Solidworks, this is a professional 3D CAD package used extensively in industry for product design.

    An EXE file has been generated to offer anybody the ability to download and view the design in 3D, you can spin the assembly, measure parts etc. This utilizes the free e-viewer software. Follow the link in the section at the end.

    For the PCB design I used a free PCB CAD application called FreePCB. This is an excellent package very easy to use. Gerber files are exported to enable manufacture of the board. There are many companies online who offer PCB manufacturing services from standard gerber files. I used Tecbridge Circuits based in Middlesex UK, the minimum order quantity is three.

    Overall Dimensions

    Connections (view from rear)


    Component Parts

    LCD Screen

    The LCD screen I chose was from Earth LCD. It is a 5.7” colour VGA screen ideally suited due to its size and compact footprint. The LCD kit comes with a separate circuit board and OSD board for on/off and setting up the screen. This particular screen came from USA however there are similar screens on offer from Farnells in the UK. The screen runs off my second graphics card and is configured 640x480 resolution as display 2

    There is a full technical specification on the LCD screen including sizes and dimensions available in the download link at the end of this document. The above image shows the screen as it is delivered , mounted on an aluminium backing plate. This can be removed, however great care is needed as self adhesive pads are used and in the bottom right hand corner they are stuck to the back of the screen over the top of a very small ribbon cable leading into the back of the screen itself.

    Some people have also used the PSone add-on screen which can be purchased from ebay quite cheaply, there is also a tutorial online for this to make it think that it is a VGA screen however from forum notes I have read this seems to have been achieved with mixed success.

    BU0836X Interface Card from Leo Bodnar


    This is a fantastic card, Windows sees it as a game controller straight away when it is plugged in to a USB port

    The card features phoenix PTSA push-in terminals for all connections so no soldering is required to connect.

    There are 32 independent digital inputs for buttons and switches. No matrix, no diodes, no daisy-chaining. Each input has its own two terminals (GND can be shared between inputs if necessary.)

    Support for up to 16 rotary encoders A pair of digital inputs can be connected to rotary encoder. All main types supported (1, 2 and 4 pulses per detent)

    8 analog inputs with true 12-bit resolution and independent wiring 4096 steps of resolution. Even 1/4 of this range is still 1024 steps!

    To support true 12-bit performance each analog inputs has independent set of +5v and GND terminals, oversampling and sophisticated signal filtering

    8-direction POV hat switch

    Compact outline of 123x52mm (4.85"x2.05") With 93 wire terminals onboard it is only 50% bigger than a credit card

    Natively supported by Windows Vista/XP/2000/Me/98, Mac OS X and Linux True Plug-and-play at its best.

    For the encoders to be setup, a small program must be downloaded and executed which stores the information on the card, this only has to be done once.

    It is important to note when wiring to the card that the encoders should be connected to button pairs 1&2 or 3&4 or 5&6 and so on.

    Custom made PCB

    The PCB was designed on FreePCB which is available to download from the Internet, Google for freepcb, don’t be afraid, this is really easy to use once you have played with it for an hour. There are also many sites on the web offering guidelines for PCB design. Mine turned out fine. Soldering to the board is really easy as there is a solder screen layer preventing the solder running off the pads.
    The board has a cut-out and holes to mount the LCD connector board. All the tracks run to the same type of Phoenix PTSA connectors used on the interface card to make connections very easy and clean.
    The board was manufactured by Tecbridge circuits in Middlesex UK who gave me a great service. Henry Gibson at Tecbridge was a great deal of help. Anybody who wishes to get them to make a board to my design, they hold the Gerber files and I have advised them that this will be out in the public domain and they have my permission to supply boards to my design. For me, this was the most daunting part of the project in starting out.

    Also try PCB Cart as they are often cheaper.

    The minimum order quantity is 3-off boards, this is done to spread the cost of tooling up to produce each board.
    A homemade PCB could also be a possibility using etching kits available from Maplins, or even prototype board if you wanted to save money, however I opted for a professionally made PCB for neatness and reliability.

    The terminal blocks I used to wire from the board are from Phoenix Contact UK – type PTSA 0.5/20-2.5-Z available from Mouser. Last time I checked they were out of stock. They can also be purchased direct from Phoenix by phone however there will be a minimum order quantity. These are the same contacts as used on Leo Bodnars card and require no screw or soldering as they have a spring cage design. Alternative would be standard ICs and ribbon cable, just remember that the PCB footprint will be different.

    Buttons and Encoders

    TL2285OA available from Mouser (and Digikey). Great little switch, very compact.

    The only down side to the switch is that the push button caps are only 10mm wide and they were difficult to apply labels to. There is also no tactile click when the switch is pressed as with a real Garmin unit. An alternate switch I would recommend is the Multimec 3FTL6 available from Farnells (or Newark in US), however this would require a PCB modification as the footprint of the switch is not quite the same.

    CTS offer a range of encoders available from Digi-key or Leo Bodnar sells them. They work flawlessly with the interface card and include a pushbutton which I mapped to Ident the VOR frequency.

    The E37 encoders from ELMA are really your only choice here, I could not find any others. I think ALPS make a similar type, but for ease I ordered them again from Leo Bodnar. He also supplies the knobs, or if you want you could buy them from Farnells. The encoders are dual rotary type so they work just like the real Garmin unit, they also have a push button built in. Wiring instruction is on Leos website.

    Custom Face plate

    The face plate is a custom design, based around the Garmin look. Although it is not identical, I think it finishes the project well.

    The part is made using a special prototyping method called SLS which is a process using photosensitive powders sintered by a laser that traces the parts cross sectional geometry layer by layer.

    The geometry is derived directly from the CAD 3D model. Most companies prefer the file in STL format, the standard file format for all rapid prototyping processes. The extension stands for Stereo Lithography but the format applies to all major rapid prototyping technologies.

    I had mine made by 11th hour prototypes now called MNL (www.mnl.co.uk) and they did an excellent job.

    They do prototyping for Dyson, Triumph motorcycles and many others.

    The cost is quite reasonable however the finishing cost is high so you may want to consider paining and finishing the part yourself. Be sure to ask them to insert some threaded brass inserts (M2 or M3).

    As an alternative to the 3D faceplate you could use a company called Shaeffer-ag (www.schaeffer-ag.de) who do CNC routed panels in Aluminium. They have a free design program you can download to design the panel and submit for manufacture, I estimate that this would be about half the cost. I currently have a panel on order from them for another project.


    To achieve the lettering for the faceplate and buttons, I used bespoke rub-down transfers from Blackham Transfers. The design for the transfer is available as a DXF file included in the download (see link at the end of this document).

    These worked really well as the whole word can be applied in one go, so everything lines up nicely as you can see from the picture on the first page.

    The pushbuttons need to be varnished once the labels are applied to prevent them from moving, for this you must use a spray on varnish. I used a satin clear varnish aerosol from our local art supply shop for £5.

    Peter Blackham holds the artwork and should be able to reproduce the labels for about £15 - £20 now that the artwork is complete.

    Google Blackham Transfers to see his website.

    He is not the best at replying to emails but his quality of work is second to none, shall definitely use him again in the future.

    The Font used for the main lettering is Franklin Gothic Book

    Letraset also do white labels in 3.5mm high lettering however they would have been too large for the pushbuttons.


    The enclosure is designed to make wiring of the unit easy. The unit can be assembled and wired without the top cover and even fat fingered people like me can manage all the wiring connections.

    The angle plate holds all the main components

    The top cover holds the OSD board for the LCD screen and has a plug connector.

    With the top cover in place the unit is fully enclosed and with rubber feet (from Poundland) underneath, can be used as a standalone desktop unit. Without the top cover the unit could easily be built into a homemade MIP (instrument panel). I Intend to build mine into a custom steel Instrument panel.

    Drawings for the enclosure are available in the download link at the end of this document together with a DXF file for the laser cutting machine.

    It should be possible to get this made locally by any good fabrication workshop for under £50.


    Reality XP GNS530 Gauge for FSX

    The Reality XP GNS530 software replicates Garmins unit almost perfectly, unlike the default Microsoft attempt. Even if you don’t wish to go so far as to build a unit like this, I can strongly recommend that you purchase this software if you are a serious flight sim “geek” and are interested in aircraft other than the big tin. For myself, it offers a great chance to practice for real world flying such is the accuracy of Reality XP’s software.

    The only downside to the software is that it is a gauge. What this effectively means is that the program installs itself as a gauge and then has to be configured for each aircraft. This in itself is okay, the biggest problem is that to my knowledge, it is not possible to run the software on a separate PC over a network and therefore I can not run FSX in full screen mode and display this gauge on a second monitor at the same time.
    In order to display the RXP GNS530 gauge on a separate monitor, it has to be undocked by right clicking the gauge and then dragged to the GarSim LCD. Once you have saved a start-up scenario this does not need to be repeated.

    However, FSX can’t now be run in full screen mode. This is the big down side for me, if anybody is aware of a solution I would be very happy to hear from you. I have heard rumours on some forum that Reality XP are possibly looking at this but as far as I am aware these are just rumours.

    Modifying the Gauge file to show the border only

    Once installed and configured to your favorite aircraft, we have to make a small modification to the panel.cfg file for that aircraft. This has to be done for the panel.cfg file of aircraft you wish to fly with this software.

    The left hand image is how the default gauge looks. We need to resize the gauge in the panel.cfg file to lose the border to fit only the map on the LCD screen. This requires the red figures below, just overwrite the original data in the line entry for the GNS gauge in your aircraft panel.cfg file. Please make a back-up first.

    C:\Program Files\Microsoft Games\Microsoft Flight Simulator X\SimObjects\Airplanes\C172\panel

    Modifying the RXP.INI file for key assignments

    As explained earlier, each button press or encoder click is recognised by windows game controller software as a joystick button input from the BU0836X. FSUIPC from Pete Dowson can map each of these button inputs to key strokes. The Reality XP software can be configured to recognize these key strokes and mapped to the various functions of the software. This is assigned in the RXP.INI file. The file is usually located here:-
    C:\Documents and Settings\All Users\Application Data\Reality XP\Common\Settings

    Below is an extract from the RXP.INI , just add the red text or assign your own. Beware of using the ALT key as this will bring up the FSX title bar.


    In order to map the keys you will need a registered copy of FSUIPC from Pete Dowson. This is well worth having anyway as it has lots of functionality to improve your sim.

    Input Assignments
    Finally we need to map each button and encoder input to a key command or key combination in FSUIPC4.INI
    To do this please read the FSUIPC4 for Advanced Users.pdf which you will find installed in your modules folder
    with FSUIPC.

    C:\Program Files\Microsoft Games\Microsoft Flight Simulator X\Modules

    The basic format of each entry in the Buttons section is as follows:
    HTML Code:
    <Entry number> = <Action><Joy#>,<Btn#>,K<key>,<shifts>
    Parts List Summary

    Downloads (divshare.com/Picasa)

    An EXE file has been generated to offer anybody the ability to download and view the design in 3D, you can spin the assembly, measure parts etc. This utilizes the free e-viewer software from Solidworks.

    More pictures are available here from Picasa

    All files for this project including the printed circuit board Gerber files together with the raw FREEPCB Data files.
    Plus all the spec sheets for the LCD screen, push buttons, encoders and drawings of the enclosure.

    For any questions, please feel free to email me directly Stevejmasters@gmail.com

    I will try my best to answer all mails as promptly as possible.

    Just to sum up, I offer this information to you as part of the flight sim community. Please understand that I am not
    an expert or specialist in cockpit building, this is my first project.
    I offer the information as a guide only, and cannot accept any responsibility bla bla bla…. You get the idea.
    Please check every step of your project yourself if you decide to have a go!!!

    Good luck and have fun building, I did!

    Steve Masters (Steve1970)