Interface Modules

Using OEM components 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 MIP has a handy storage area for the mounting of various interface cards, it is not large enough to cater towards the numerous cards, busbars and wiring required.

Systems Module Concept

In the real Boeing aircraft, 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.

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, to enable air circulation, are located on the side of the module adjacent to *'mouse holes'* (just visible in image). 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 has been turned on

Trail Module

To determine if the modular concept would be feasible, an Interface Master Module (IMM) was constructed and trailed. The evaluation of the trial IMM was successful (images of trial IMM). Following on from this trail IMM, three interface modules have been constructed. Each module pertains to specific aircraft systems.

Although the modules contain 90% of the interface cards, some cards have been mounted in more traditional areas such as the MIP shelf 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 (the joystick controller cards are installed inside a small dust proof box).

Other interface cards specific to a panel 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.

Important Note:

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

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’ accessible from the main menu.

The following modules are used:

Throttle Interface Module (TIM)
Throttle Communication Module (TCM)
Overhead Interface Module (OIM)
System Interface Module (SIM)
System Interface Module (SMART)
Interface Alert System (IAS) - forms part of TIM and TCM
Power Management Button System (PMBS) - forms part of TIM

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 - IAS) provides a visual warning in the event that a particular system is not functioning correctly. Additionally, a sub system called the The Power Management Button system (PMB) enables power to be turned on or off to specific sectors within TIM.

The Throttle Interface Module is the most important module (primary module); therefore, this module has 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. These lights are located on the forward side of the module.

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 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 (SIM-1, SIM-2 and so forth).

The System Interface Module (SMART) - SMART is used to house the interface cards and other ancillary devices needed to control several OEM components. Namely, the flaps, Auto Pilot Flight Director System (AFDS), korrys, system annunciators (six packs), fuel flow reset and autobrake system. SMART also enables various voltages to be stepped down to enable specific OEM components to function correctly, in addition to enabling the flaps gauge to be calibrated using 400 hertz. Considering what the module does, is the reason it was called SMART.

The Interface Alert System (IAS) is not a module per se, 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 push on/off coloured LEDS, called 'traffic lights' enables specific sectors within a module to be turned on/off by opening or closing the circuit.

A specific combination of lights flashing or solid can 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 develops, 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' accessible from the main menu tabs.

Advantages in 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 expansion by allowing addition of further modules (as required).

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

The Modules

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

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 for easy access, 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 any wiring and interface card should maintenance or 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 (TIM), brushless fans are strategically located along with ‘mouse holes’ to ensure adequate ventilation and cross-circulation of air.

Connection and Cables

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 either mounted directly within the module or comes from the Power Supply Rack. The use of a hub facilitates the connection of the various cards inside the module to the computer using one USB cable.

Throttle Communication Module (TCM) that forms part of 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. The LEDS that form part of the IAS can be seen between the two upper connectors

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 components. 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. The number of straight-through cables used will depend on the module’s use and the number of interface cards it accommodates.

To remove the chance that a straight-through cable is mated to the incorrect D-Sub connection, all cables are colour coded and appropriately 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.

TIM 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

The use of straight-through cables also allows the wiring to be 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 components.

Busbars

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.

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 components.

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 and Documentation

**Table 1** provides an overview of the cards used, their functionality and location. Note that this changes as OEM components are added to the simulator

Without documentation you will soon become lost with regard to what you have or have done. Interface card architecture is a simple document that records what interface cards and other components have been used, and what functions they are responsible for in the simulator.

Final Call

It has taken considerable time to design, fabricate, 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.