This is the second System Interface Module (SIM) and is a continuation of the system modular approach.  System modules are designed to allow expandability and to segregate like-minded parts into systems - which is the same philosophy that Boeing uses with the real Boeing aircraft. To differentiate this module from others, it has been named SMART.

LEFT:  Plan photograph of SMART.  The module is resting on the center pedestal which gives a good indication to the overall dimensions of the module.  The 400 hertz module is the grey-coloured box whilst the Flap Calibration and Coupling Mechanism is adjacent.  The relays, busbars, four-plug USB hub, and voltage step down controllers are obvious, as are the two Phidget cards that control the dual AFDS units.  Colour-coded VGA connectors, which support straight-through cables are mounted to the module's firewall (click to enlarge).

The construction of this module is identical to the other interface modules used in the simulator, with the exception that this module does not have accessory indicators such as the voltage, Hobbs an, amperage gauge.  Nor does it have an interface alert system. 

SMART was primarily designed to accommodate the framework required to calibrate and operate the OEM flaps gauge; however, the module also incorporates other functionality.

All components supported by SMART are Original Equipment Manufacture (OEM).  OEM parts are real Boeing 737 parts, that for whatever reason have been discarded from service.

Interface Cards, Functionality and Integral Components

SMART provides the functionality for the following aircraft components. 

NOTE:  The letter A refers to items that connect to one of two Phidget cards, while letter B  signifies sole use by the flaps gauge.  No letter indicates the items are used by both A & B.

(i)        Autopilot Flight Director System (AFDS) Captain (A);
(ii)       Autopilot Flight Director System (AFDS) First Officer (A);
(iii)      Master Caution System (fire bell & master caution annunciators) Captain (A);
(iv)      Master Caution System (fire bell & master caution annunciators) First Officer (A);
(v)       System Annunciator Panels (aka six packs) Captain (A);
(vi)      System Annunciator Panels (aka six packs) First Officer (A);
(vii)     Fuel Flow toggle switch (MIP) (A);
(viii)    Auto Brake System selector (MIP) (A); and,
(ix)     Flaps gauge (MIP) (B).

SMART houses the following interface cards and parts:

(i)       Two Phidget 0/16/16 interface cards (Captain & First Officer) (A);
(ii)      Two 12 volt brushless fans;
(iii)     12 volt busbar;
(iv)     28 volt busbar;
(v)      Four relay modules (temperature, 400 hertz (2) and advanced flaps calibration) (B);
(vi)      5 and 12 volt step down controller;
(vii)     OEM aircraft 400 hertz inverter unit (B);
(viii)     Left pointer (slave) flaps calibration and coupling mechanism (FCCM) (B);
(ix)      Right pointer (master) flaps calibration andcoupling mechanism (FCCM) (B);
(x)       Four pull/throw toggles (B);
(xi)      Two Phidget Advanced Servo cards (B);
(xii)      Belkin 4 USB powered hub; and,
(xiii)     Internal temperature sensor.

To operate the OEM components, other than the flaps gauge, two Phidget 0/16/16 cards are used; one card for the Captain side and the other card for the First Officer side components.  The reason for the segregation is to enable easier troubleshooting should a problem occur.   Furthermore, the wires from each unit have been colour-codes and labelled for easier identification.

The auto brake system selector and the fuel flow toggle use inputs and outputs that have not been used in the above-mentioned Phidget 0/16/16 cards.

To operate the OEM flaps gauge correctly, components (vii) through (x) from List 2 are required.   The most important piece of equipment is the 400 hertz inverter unit which is used to power the movement of the two needles in the flaps gauge.

400 Hertz Inverter

400 Hertz is a type of electric power that is the standard of the commercial aircraft and aerospace industry because of its lightweight, its high power, and its proven reliability.  It is the primary power on all commercial and military aircraft.

LEFT:  Aircraft 400 HZ inverter unit - a small item that packs quite a bit of punch when it comes to power output.

An inverter is an electronic device that takes in 50HZ or 60HZ power and rectifies it to D.C. and then reduces this to different frequency, which in our case is 400HZ.  Inverters are small, light and pack considerable punch when it comes to electrical output, which is why they are chosen to be used in the aviation and the aerospace industry (small size and low weight equate to dollars saved).  They also provide ground fault protection, soft start capability, overload protection and variable motor RPM.

Connection and Function

To enable connection to the server computer via one USB cable, a 5 volt powered Belkin 4 port USB hub has been used. 

Three straight-through cables are connected  to SMART and marry with their respective OEM components –  the Captain-side AFDS unit, First Officer-side AFDS unit, and the flaps gauge.  The autobrake and fuel flow switch have respective wires with terminals that form part the straight-through cable used for the flaps gauge.

SMART incorporated two push in style buttons are mounted in the firewall of the module.  A solid green-coloured LED button, located on the module’s firewall provides a ready indicator that the SMART is turned on and operational.  The lower red-coloured LED (if depressed) allows the accessory plug (discussed below) to receive 400 hertz from the inverter unit.

Power requirements and Cooling

Power requirements for SMART are 5 and 28 Volts.  The former is for the backlighting of the Flaps gauge, while 28 Volts is required for the illumination of the various annunciators in the Master Caution System (MCS) and AFDS units.  

LEFT:  One of two voltage step down modules and the Phidget card that controls the First Officer side AFDS unit.  Note colour-coded wiring which aids in wire identification (click to enlarge).

The power supply for the 28 volts is standalone and resides in the power supply rack, while the 5 and 12 volt power is internally generated through the use of a 5 and 12 volt step down controller.  

The step down modules are mounted within the SMART module.  The benefit of using step down modules is two-fold.  It limits the number of wires connected with outside power supplies, whilst taking full advantage of using only one external 28 volt power supply.

LEFT:  28 volt busbar, internal temperature probe (SMART probe) and grey-coloured 400 hertz unit (click to enlarge).

The components that are installed within the module, for the most part, do not generate heat; however, the 400 hertz inverter unit does generate considerable heat (1).  

To facilitate cooling if and when required, two 12 volt brushless fans have been installed either side of the inverter in the side walls of the module.  An internal temperature probe (SMART probe) will, dependent upon the generated internal ambient temperature (currently 88F), automatically turn the fans on or off. This is accomplished by the use of a relay.

Advanced Features - Why SMART is called SMART   

OEM gauges, for the most part, require 400 hertz to operate correctly.  This is especially so for any gauge that has a needle or dial that moves.

An advantage of using an aircraft inverter is that the 400 hertz power the inverter generates is more than enough to operate more than one gauge.  Therefore; to harness this power for additional OEM gauges (such as in the overhead panel), SMART has been installed with an accessory plug to distribute 400 Hertz to other connected gauges.  

Pull/Throw Toggles (accessory gauges and calibration)

If you look carefully at the picture of the SMART module, you will note four pull/throw toggles mounted along the sides of the module.  The toggles are used to facilitate the following:

LEFT:  400 hertz calibration toggle and LED.  When placed to CALIB the system receives constant 400 hertz and the LED will flicker several colours (click to enlarge).

Toggle 1:   This toggle, when selected from NORM to AUX enables an additional 28 volt power supply to be connected to the module.  This may be necessary if additional gauges, that use 400 hertz, require a direct power supply.

Toggle 2:  This toggle, when selected from NORM to AUX enables 400 hertz to travel to the plug located in the firewall of the module.  The plug facilitates the connection of additional OEM gauges that utilise 400 hertz.  The toggle operates in unison with the red-coloured button mentioned earlier in the post.  The toggle must be selected to AUX and the button depressed to enable the distribution of 400 hertz.

Toggle 3:  Toggle 3 is used during the initial calibration of the flaps gauge.  This toggle when moved from NORM to ADV facilitates manual calibration of the two pointer needles, so they align above each other and move as one pointer.  ADV is also selected to energise asymmetric flaps operation  (currently not implemented in ProSim737 avionics suite).

Toggle 4:  Toggle 4 is labelled NORM/CALIB.  When calibration is selected, the inverter will constantly generate 400 hertz.  A Constant 400 hertz is required at anytime the flap gauge is being calibrated.  This toggle also an LED, which shows a flashing multi-coloured light.  The LED serves to indicate that the unit is generating 400 hertz and/or is in calibration mode.

(NORM = normal, CALIB = calibration, AUX = auxiliary, ADV = advanced).

Flaps Calibration and Coupling Mechanism (FCCM)

The two  flaps calibration coupling mechanisms are used solely to calibrate the flaps gauge.  Two hex keys are used to unlock the coupling of the FCCM.  This enables the shaft of the FCCM to be manually rotated; thereby, aligning the left and right pointers with each other in the flaps gauge.

LEFT:  There is no comparison between a reproduction flaps gauge and a reproduction.  The flaps gauge installed (complete with dust).  The OEM flaps gauge was the prime reason SMART was developed (click to enlarge).

Asymmetric Flaps

The ProSim737 avionics suite does not currently (August 2015) simulate asymmetric flap operation; however, SMART is ready if this function is implemented – for asymmetrical flaps to operate the toggle must be selected to ADV.

LEFT:  OEM flaps gauge which SMART was initially designed to calibrate, power and operate.  The left and right points used during asymmetric operations are clearly evident.  For normal operation, the two needles are aligned in so kuch that they move as one needle.  MIP attachment bracket not shown (click to enlarge).

Further information concerning the flaps gauge, mechanism and operation will be documented in an additional post (to be written with link provided here).


FCCM – Flaps Calibration and Coupling Mechanism (used to manually calibrate the two flap pointers when 400 hertz is applied).
MCS – Master Caution System (encompasses the fire bell, master warning and system annunciators aka six packs).
OEM – Original Equipment Manufacture.

Foot Note

(1:)     The amount of heat generated by the FCCM and the 400 hertz inverter unit is reflected by the length of time that the unit is engaged.  The inverter is energised only when the flaps are being moved or are in the extended position.  When the flaps are retracted and flaps movement ceases, a relay is activated that turns the inverter unit off.

(2):    All the parts that this module supports are Original Equipment Manufacture (OEM). OEM parts are real Boeing 737 parts that for whatever reason have been discarded from service.