Journal Archive (Newest First)


INTERFACE MODULES -  Introduction (updated 08 March 2015)

Using real aviation parts (Original Equipment Manufacture / OEM) requires several interface and relay cards, quite a bit of wiring, and several power supplies of differing voltage.  A potential problem is where to mount the interface cards, and how to wire the components without creating a ‘rat’s nest’ of wire.

The obvious location is to attach the interface cards directly to the rear of the Main Instrument Panel (MIP), and although the Flight Deck Solutions (FDS) MIP has a handy storage area for the mounting of various interface cards, it is not large enough to cater towards the number of cards, busbars and wiring needed to interface real aircraft parts.  

Systems Module Concept

In the real Boeing aircraft, systems comprise similar avionics.  The simulator replicates this principle by housing specific system-orientated interface cards in specific custom-designed modules. The housings being modular can either be stacked on top of each other or mounted forward of the simulator.

LEFT:  Throttle Interface Module (TIM) showing LED Interface Alert System (IAS) on the upper lid of the unit, system lights (traffic lights) and the two main cooling fans.  Additional cooling fans are located on the side of the module adjacent to 'mouse holes' (just visible in image) to allow air circulation.  Voltage and amperage gauges are located on the upper lid. A Hobbs meter is also included to monitor the period of time that the system hss been turned on  (click to enlarge).

Trail Module

To determine if the modular concept would be feasible, a Interface Master Module (IMM) was constructed and trialed.  The evaluation of the trial IMM was successful (images of trial IMM).  Following on from this trail IMM, three interface modules have been constructed.  The Throttle Intereface Module (TIM) being the primary module.

Although the modules contain 90% of the interface cards, other cards have been mounted in more traditional areas such as the MIP storage area and, for the joystick controller card that controls the flight controls, to the underside of the platform in front of the captain-side control column. 

Other interface cards specific to a panel/module are mounted directly within the unit – these units are literally ‘plug and fly’.  Examples of these units are the fire suppression panel (fire handles), radar panel and audio control panels (ASP units) mounted in the center pedestal.

NOTE:  The simulator predominately uses Original Equipment Manufacture (OEM) parts.  These surplus parts were once used in an actual Boeing 737.  The requirements to facilitate the operation of these parts is varied; as such, the various interface modules are designed around the use of OEM parts.

Interface Modules - An Overview

The following provides an overview of the interface modular concept and introduces the modules that are used in the simulator.  Further information on each module is available in the appropriate section named ‘Interface Modules’ on the main menu.

The following modules (titles are links) have been used, in addition to an Interface Alert System (IAS):

•    Throttle Interface Module (TIM)
•    Throttle Communication Module (TCM)
•    Overhead Interface Module (OIM)
•    System Interface Module (SIM)

The Throttle Interface Module (TIM) houses the various interface cards used in the operation of the throttle, including the automation.  Additionally, the module incorporates amperage and voltage meters and a Hobbs meter.  The latter is used to measure the number of hours that power has been applied to the interface cards.  A system of LED lights (part of the Interface Alert System) also provides a visual warning in the event that a particular system is not functioning correctly.  The Throttle Interface Module is the most important module (primary module); therefore, this module has most of the additional features that other modules may lack.

The Overhead Interface Module (OIM) will house all cards associated with the forward and aft overhead.  This module is yet to be constructed and implemented.

The Throttle Communication Module (TCM) is mounted directly to the forward edge of the Throttle quadrant and contains all the components required to facilitate communicate between the Throttle Interface Module and the throttle unit.  Additionally, it incorporates a rudimentary system of three different coloured LEDS to indicate correct operation.

The System Interface Module (SIM) is used to house interface cards belonging to other systems not included in the forward and aft overhead or throttle quadrant; for example the korrys that are used in the Main Instrument Panel (MIP), the landing gear and some the avionics located within the center pedestal.  The System Interface Module, if necessary, can be expanded by adding additional modules.

The System Interface Module (SMART) - SOON

The Interface Alert System (IAS) is not a module, but a system of LED lights attached to the Throttle Interface Module (TIM) and Throttle Communication Module (TCM).

The purpose of the IAS is two-fold.  First, the IAS provides a visual warning that a problem exists within a module; and secondly, a series of coloured LEDS, called 'traffic lights' enables specifc sectors within a module to be turned on/off by opening or closing the circuit.

A system of coloured LEDS is used to indicate:

(i)    Power connection;
(ii)   Wire continuity between cards and their OEM components; and,
(iii)   Connectivity between sub-systems.

If a problem occurs with any of the interface cards or wiring within a connected module, or a power issue is noted, the LEDS will illuminate in a pre-defined colour arrangement indicating which system is inoperative. 

Initially, the Interface Alert System was going to be used for all modules; however, it was decided that the IAS was not required for the System Interface Module (SIM).  Therefore, the IAS has only been incorporated, at differing levels, into the two most important modules – the Throttle Interface Module (TIM) and the Throttle Communication Module (TCM).  

To read more information on each module, navigate to ‘Interface Modules' in the main menu tabs.

Benefits of Modular Design

The advantages in using system modules are:

(i)    It accommodates like-minded components used in a particular aircraft system;
(ii)    It enables easier troubleshooting and replacement of an interface card if a problem is detected;
(iii)   It provides physical protection for the storage of delicate interface cards;
(iv)   It enables a central area for the mounting of interface cards, relays, etc; and,
(v)    It allows expanability by allowing addition of further modules (as required).

Construction, 'Whitespace' and Temperature Control

The construction of the modules is straightforward.  A box-like structure with a screw down-lid was constructed from ABS plastic and plastic welded to ensure strength and longevity. 

LEFT:  Portion of Throttle Interface Module (TIM) showing raised internal blocks (pale white) for mounting interface cards and one of several female colour-coded D-Sub plugs.  The top of the module has been removed (click to enlarge).

The benefits of using ABS plastic over acrylic are that the former is not brittle when drilled.  Trials using acrylic plastic were not favourable as drilling and continual tightening and loosing of screws caused the material to crack.

Furthermore, rather than use screws to attach the lid, the modules were designed with hinged lids and/or thumb screws to secure the lid to the body of the module.

To mount the interface cards and busbars within a module, a raised platform constructed from ABS plastic has been used.  These platforms are then directly attached via screws to the inside of the module.  This makes it relatively easy to remove an interface card should replacement be necessary.

An outcome from the evaluation of the trial Interface Master Module (IMM) was that there was not enough room around the installed cards to easily manipulate wires if a repair was required.  Another shortcoming was that wire was not colour-coded.  This caused confusion when dealing with multiple voltages.  Therefore, the new design incorporates additional ‘white space’ around each module and specific wiring is colour-coded.  Ferrules have also been used on all wires that are connected to an interface card.  The use of ferrules enables easier removal of wires from an interface card.

To control the ambient temperature inside the modules, especially for those modules that include a power supply, brushless fans are strategically located along with ‘mouse holes’ to ensure adequate ventilation and cross-circulation of air.

Connection and Cables

LEFT:  Five dedicated VGA cables that connect from the Throttle Communication Module (TCM) to the Throttle Interface Module (TIM).  The information that travels through these cables provides the logic to operate everything associated with the throttle quadrant.  The TCM is attached to the forward portion of the throttle quadrant (click to enlarge).

Depending upon the system, any number of interface cards are accommodated within a module; each card requiring a USB connection to the computer.  To avoid having to use multiple USB cables which look unsightly, and can be a cause of intermittent connection failure, a powered high capacity Belkin mini-hub has been mounted inside each module. 

The power supply for the hub is mounted directly within the module.  These hubs facilitate the connection of the module and the various cards it contains, to the computer using one USB cable.

All the interface modules incorporate VGA and serial port connections (D-Subs).  This reduces the volume of wiring that leaves the module to various OEM parts.  Mating with the connections are straight-through cables that incorporate tightening screws.  Once a straight-through cable is attached and secured to the module firewall, there is no chance that the cable will work its way loose causing an intermittent connection. 

To remove the chance that a straight-through cable is mated to the incorrect D-Sub connection, all cables are colour coded and appropiately labelled.  Furthermore, some connections are VGA male and others female, while others are serial.  This removes the possibility of incorrectly mating the wrong cable with the wrong connection.

The use of straight-through cables also allows the wiring to relatively neat and tidy. 

The receiving end of the straight-through cable is to a D-Sub mate mounted on a bracket which is attached to the Main Instrument Panel (MIP).  From this bracket various wires are bound within a lumen and navigate to the various OEM parts.


A bus bar is a small brass bar connected to a power supply that runs a specific voltage.  It enables connection to a number of modules that require the same voltage for operation.  The simulator has several multi-voltage busbars strategically located. 

LEFT:  TIM - another angle showing the detail of the raised blocks on which the I/O cards are directly mounted.  Also shown are the three speed controller used to control the speed rotation for the stab trim wheels (click to enlarge).

A 5 and 28 volt busbar is located within the center pedestal while a primary 28 volt busbar is located on the rear of the MIP.  Several additional busbars are located within the Throttle Communication Module (TCM).

Location of Interface Modules

The modules are small enough in size that they are portable.  While this provides the obvious advantage that they can be easily removed to a work bench, it also enables the modules to be strategically located in any location proximal to the simulator, providing there is a connection to the Power Supply Rack (PSR) and the straight-through cables are long enough to reach their respective parts.

The modules are mounted on a small three-shelf bench that is located forward of the Main Instrument Panel on the First Officer side. The bench is large enough to adequately store the modules while allowing  accessibility.

Interface Card Architecture

Interface card architecture refers to the type of interface cards used and the functionality they relate to.

Table 1 provides an overview of the cards used, their functionality and location (click table to enlarge).

Final Call

It has taken considerable time to design and construct and then interface these modules to the simulator.  To some, the process may appear complex and convoluted.  However, the concept is sound and offers considerable advantages - especially in relation to troubleshooting.

Additional photographs can be found in the picture gallery.

Nomenclature and Acronyms

OEM  - Original Equipment Manufacturer (real aviation part).
TIM  -  Throttle Interface Module.
IAS  -   Interface Alert System.
OIM  -  Overhead Interface Module.
TCM  -  Throttle Communication Module.
SIM  -  System Interface Module.