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Mission Statement 

The purpose of FLAPS-2-APPROACH is two-fold:  To document the construction of a Boeing 737 flight simulator, and to act as a platform to share aviation-related articles pertaining to the Boeing 737; thereby, providing a source of inspiration and reference to like-minded individuals.

I am not a professional journalist.  Writing for a cross section of readers from differing cultures and languages with varying degrees of technical ability, can at times be challenging. I hope there are not too many spelling and grammatical mistakes.

 

Note:   I have NO affiliation with ANY manufacturer or reseller.  All reviews and content are 'frank and fearless' - I tell it as I see it.  Do not complain if you do not like what you read.

I use the words 'modules & panels' and 'CDU & FMC' interchangeably.  The definition of the acronym 'OEM' is Original Equipment Manufacturer (aka real aicraft part).

 

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Journal Archive (Newest First)

Entries in Simulator Solutions (1)

Friday
Jun232017

OEM B737 CDU Conversion - Using SimStacks To Convert The CDU

This article follows on from an earlier post that introduced the concept of converting an OEM CDU to use in flight simulator.  The conversion has now been completed and the CDU operates seamlessly with ProSim-AR. 

LEFT:  OEM CDU fully converted and operational.  The CDU is from a classic 500 series aircraft.  Prior to my ownership, the CDU was used by United Airlines (click to enlarge)

Historical Conversion Techniques

To date, various OEM parts have been converted using Phidget cards, and to a lesser extent Leo Bodnar cards, Flight Deck Solutions system cards, and PoKeys interface cards.  Phidgets provide a stable platform, despite the disadvantage that they, at time of writing, only connect via USB to the server computer.  The primary advantage of using Phidgets is that they have been used in a wide variety of applications, are inherently stable (for the most part), and their configuration is well documented.

The conversion of the CDU was slightly different to the norm, in that a different interface system was used. 

SimStacks by Simulator Solutions

The conversion of the CDU was done in collaboration with Sydney-based company Simulator Solutions Pty Ltd.  Simulator Solutions utilise their propriety interface boards called SimStacks to convert OEM parts for use in commercial-grade simulators

SimStacks is a modular, stackable, and scalable hardware interface that is designed to integrate OEM parts into your simulator with little or no modification.    One of the many advantages in using a SimStack Foundation Board (SFB) is that the interface can connect with either the server or client computer via Ethernet (as opposed to Phidgets). 

To date, Simulator Solution’s experience has been predominately with the conversion of B747 parts and Rodney and John (owners) were excited to have the opportunity to evaluate their software on the 737 platform, with the 737 CDU being the ‘first cab off the rank’.

This article will not delve deeply into the SimStack architecture, nor will it document the wire pin-outs used with the interface card; a future post will tackle this topic in more detail. 

CDU Conversion - Choose Your Poison

There are two main camps when discussing how to convert an OEM part.  The first is to utilise as much of the original wiring and parts as possible.  The second is to completely ‘gut’ the part and convert it cleanly using an interface that connects seamlessly with the avionics software in use (ProSim-AR).  A third option, although expensive and in many respects ‘experimental’, is to use ARINC 429.

With regard to the CDU, the easiest route was option two; everything in the CDU was removed with the exception of the internal shelf divider and keypad.  In hindsight, the pin-outs of the Canon plugs could have been used, but to do so a female Canon plug would have been required, and for the use of a couple of pins, this seemed to be overkill.

Keypad and Screen

The keypad and screen are the two most important parts of the CDU, and it's vital that the connection between the keypad, screen, and the SimStacks Foundation Board is not compromised.  The actual functionality of the CDU is controlled by the avionics suite.

Keypad

The keypad forms part of the lightplate in which 5 Volt incandescent bulbs are strategically located to ensure even backlighting of the keys.  Disassembling and removing the keypad from the main body of the CDU is straightforward; several small Philips head screws hold the keypad in place.  Once the keypad has been removed, any ‘blown’ bulbs can be replaced. 

Table 1: Overview of bulb location, part number and quantity.

The keypad has several wires that connect to a terminus inside the main body of the CDU.  Care must be taken when cutting the strands of wire to ensure the connection between the terminus and the keypad is not damaged.  Depending upon your skill, the terminus can be removed and a longer wire soldered to the keypad connector, or the wire can be lengthened (by splicing).  The wires from the terminus connect with the SimStack Foundation Board.

CRT and LCD Screen

The Classic CDU is fitted with a solid glass cathode ray tube (CRT) screen.  The CRT screen is approximately 2 cm thick and fits snugly within the display frame of the CDU. 

LEFT:  The CRT screen forms part of the CDU casing.  The silver coloured foil indicates the thickness of the replacement glass that needed to be ground (click to enlarge).

It’s possible to make the CRT screen operational, however,  the display would be monochromatic (green) and the screen resolution poor.  Therefore, the CRT was replaced with a custom-sized high resolution colour LCD screen.

To retrofit a replacement screen is not without its challenges.  The LCD screen is not as thick as the CRT screen, and is also not the same shape.  Therefore, the screen will not fit snugly within the display recess.  To rectify this shortfall, a piece of clear glass was ground to correctly fit within the display frame of the CDU.  This piece of glass replaces the 2 cm thick CRT glass.  The thin LCD screen was then mounted behind the clear glass in a central position.

During the design phase, it was thought that the thick piece of glass would cause a refraction problem.  However, although the theory suggests refraction will occur, the practical application has been such that any refraction is not readily noticeable.

Mounting the LCD Screen

Mounting the LCD screen can be done a number of ways.  Commercial grade double-sided sticky tape is the easiest method, but it is rudimentary.

LEFT:  LCD screen is fitted and temporarily held in position by commercial tape and a foam spacer.  Prior to revamping the CDU, this area was used to house the very large square shaped CRT screen.  Note the ribbon cable linking the screen to the screen interface card and the two white cables that connect to the screen controller card and SFB (click to enlarge).

To secure the LCD so that the screen sat firmly against the glass, thin metal plate was used to replace the open space that was left after removal of the CRT screen.  The sides of the metal plate were fabricated to push against the rear edge of the LCD.  This firmly secured the LCD screen against the rear of the clear glass.

LEFT:  The photograph shows the metal plate that was fabricated to replace the original CRT unit.  The edge of the plate pushes against the rear of the LCD screen holding the screen in place.  To remove the plate cover, 2 screws need to be removed.  It's amazing that the CRT screen required the amount of space that it did  - about 5 inches square! (click to enlarge).

Although the use of metal plate appears slightly unattractive, the plate only serves to enclose the CDU.  Once the CDU is slid into the CDU bay, the the casing of the CDU is not visible.

An alterative to using metal plate is to use ABS plastic painted the correct Boeing grey colour.

SimStack Foundation Board, External Wires and Screen Controller Card

To ensure that the CDU is standalone and will function without external inputs other than power supplies, four items need to be mounted inside the CDU.

(i)    The generic Interface card that controls the LCD screen;
(ii)    The LCD screen controller (buttons that control brightness, contrast, etc);
(iii)   The SimStack Foundation Board; and,
(iv)   The wiring to connect the keyboard to the Foundation Board.

Fortunately, there is ample room in the cavernous interior of the CDU to fit these items.

LEFT:  SimStack Foundation Board (SFB) mounted into the lower section of the CDU casing.  The SFB is responsible  for registering the key presses made on the keypad which are then deciphered and communicated to the avionics suite (ProSim-AR).  Click to enlarge.

The SimStack Foundation Board is mounted on an angular metal bracket that is attached directly to the bottom of the CDU, while the LCD interface card has been installed on the upper shelf along with the screen controller.  A ribbon cable connects the LCD screen to the interface card while a standard VGA cable connects the LCD screen to the client computer. 

The SimStack Foundation Board is Ethernet ready and requires a standard Ethernet cable (CAT 6) to connect from the card to an Ethernet switch (located behind the MIP). 

In addition to the Ethernet  and VGA cable, six power wires leave the CDU via the rear of the casing; four from the SimStack Foundation Board (5 and 12 volts +-) and two from the keypad (5 volts +-) to control the backlighting.

Toggle Switch

A standard two-way toggle switch is mounted to the rear of the CDU casing.  This switch is used to control whether the LCD screen, used in the CDU, is always on, or is only turned on when ProSim-AR is activated.  The switch is set and forget, however, access to the switch can be made from the front of the MIP or by sliding the CDU our of the CDU bay.

LEFT:  Toggle switch and wire harness leaving the base of the CDU casing.  The switch position and harness use the existing holes in the casing that were previously used by the Canon plugs.  5 and 12 volt wires are connected to appropriate busbars behind the MIP, while the VGA cable connects with the client computer.  The Ethernet cable connects into the Ethernet switch, also mounted at the front of the MIP (click to enlarge).

Power Supply

To operate the CDU requires a 5 and 12 volt power supply.  The backlighting of the keypad is powered by 5 volts while the SimStack Foundation Board and CDU operation require 12 volts.

Backlight Dimming

On my set-up, to enable the CDU keyboard to be dimmed, the 5 volt wires that leave the lower section of the CDU, are connected to a dedicated 5 volt Busbar located in the center pedestal.  This Busbar is used to connect the backlighting from all OEM panels.  The Busbar is then connected to the panel knob on the center pedestal.  The ability to turn the backlighting on and off is controlled by opening or closing a 12 volt relay (attached in line between the panel knob and Busbar).  Dimming is controlled by a dimmer circuit.

Mounting the CDU to Flight Deck Solutions MIP

The MIP skeleton and CDU bay is manufactured by Flight Deck Solutions (FDS), and is designed to fit FDS’s propriety CDU unit (MX Pro) and not an OEM unit.

The casing for the OEM CDU is much longer than the FDS CDU and measures 24 cm in length.

The FDS MIP incorporates an aluminum shelf (used by FDS to mount various interface cards) that protrudes slightly into the CDU bay.  This protrusion stops the OEM casing from sliding all the way into the bay.  To enable the CDU casing to slide fully into the bay, a small section of the shelf must be cut away.

A small metal saw is used to trim the metal away from the shelf, and although an easy task, care must be taken not to ‘saw away’ too much metal.  Once the piece of offending aluminum is removed, the casing of the CDU slides perfectly into the bay, to be secured by the DZUS fasteners to the DZUS rail.

LEFT:  Using a small metal saw, s small section of the shelf is removed.  This enables the CDU to slide into the CDU bay.  Left image is the shelf projecting into the CDU bay while the right image shows the shelf removed and covered in protective tape (to minimise abrasion).  A small notch was made at the corner to facilitate the safe routing of the wires used to enable the Lights Test (click to enlarge).

Functionality and Operation

The CDU is not intelligent; it’s basically a glorified keyboard that requires interfacing with software for functionality.  The functionality, fonts, colour, etc are provided by the avionics suite (in this case ProSim-AR, but arguably it could also be Sim Avionics or Project Magenta). 

To enable communication between the avionics suite and the SimStack Foundation Board (in the CDU casing), SimStack proprietary software must be installed.

SimStack Software - SimSwitch

SimSwitch is installed on the client computer and when configured interfaces with ProSim-AR on the server computer and the network.  Configuring SimSwitch is straightforward and involves inputting the correct static IP address and port numbers.

LEFT:  Screen grab showing SimSwitch software interface.  This is located on the client computer.  The interface, once configured, is standalone.  The software can easily be opened in minimized mode via a batch file (click to enlarge).

SimSwitch can also be used to monitor all connected OEM panels and provide debugging information if needed.

SimSwitch is a JAR archive executable file.  The file must be in operation to eanable the CDU to communicate with the avionics suite. 

The JAR file and the ProSim CDU .exe file must both be open for the CDU to function correctly.  To expedite a simulator session, the JAR file can very easily be added to a batch file for automatic loading of software prior to a simulator session.  A timer command can be added to the batch file line ensuring the JAR file opens before the ProSim CDU.exe file. 

First Officer CDU

The First Officer CDU will be converted using a similar technique, with the exception that this unit will be converted more ‘cleanly’.  A dedicated plate (rather than an angular bracket) will be fitted to the inside of the CDU casing.  This will facilitate the mounting of the SimStacks Foundation Board and LCD screen controller card.

Additional Photographs and Video

Additional photographs can be viewed in the image gallery.

BELOW: A short video demonstrating the operation of the OEM CDU using ProSim-AR. 

Main points to note in the video are:

(i)    Heavy duty tactile keys;
(ii)   The definite click that is heard when depressing a key;
(iii)  The solid keypad (the keys do not wobble about in their sockets); and,
(iv) Although subjective, the appearance of the OEM CDU looks more aesthetically pleasing that a reproduction unit.

Final Call

This conversion, by using a SimStack Foundation Board (SFB), has enabled full functionality of the OEM CDU using ProSim-AR.  The SFB can also be used to connect with other avionics suites, such as Sim Avionics and Project Magenta.  However, although the wiring of the SFB would be identical, the way in which the card interfaces and communicates with the avionics suite will differ.

Glossary

ARINC429 –  A standard used to  address data communications between avionics components.  The most widely used  standard is an avionics data bus.  ARINC 429 enables a single transmitter to communicate data to up to 20 receivers over a single bus.

SFB - SimStacks Foundation Board.

Standalone – Two meanings.  (i)   Operation does not require an interface card to be mounted outside of the panel/part; and, (ii)  In relation to software, the executable file (.exe) does not need to be installed to C Drive, but can be executed from any folder or the desktop.