L-1011 Trainer: Digital and Analog Bus Integration

Digital and Analog Integration Planning

L-1011 Digital I/O Bus

To make the simulator work there are a number of hardware integration methods that we need to put in place to allow the actual flight hardware to interact with the simulator software and vice versa. We need to be able to do the following:

Digital Input and Output (I/O)

Digital I/O is used to read switch states (on/off) as well as setting of annunciator lights. A large amount of digital I/O channels are needed to drive the L-1011 cockpit. All in all, there will be a need for 530 Output Channels as well as 582 Input Channels. The digital I/O bus also needs to be highly distributed across the sim (FE Station, MIP, Overhead, etc) and it needs to be resistant to electrical noise and power transients. Since everything in the simulator operates on either 24VDC or 115V AC ... the Digital I/O system needs to be able to directly interface with 24VDC without much need to do signal conditioning prior to entering the I/O interface (e.g. TTL level conversion). Digital Output will also need to be done mostly on 24VDC and will need to be able to be sourced as well as sunk.

Analog Input and Output (AIO)

The simulator instruments will required a number of analog signals to be generated. These generated analog signals will simulate the aircraft sensors. For example, engine tachometer signals need to be generated the same way they would be sent from the engine transducers to the instruments. Also, many of the flight controls will, of course, produce analog input signals to the simulator software which need to be digitized. For example, movement of the yoke or the flight control trim. So there is a need for a great amount of Digital to Analog (DAC) as well as Analog to Digital (ADC) conversion.

ARINC 429 Protocol 

Some of the primary navigation as well as attitude control instruments use the ARINC 429 bus protocol. The correct protocol needs to be generated and sent to the simulator hardware to display the right navigation and attitude data.

Overall

Since the simulator will be used in a museum and public setting where safety and reliability is of most  importance, it is critical that we use industrial strength, serviceable and commercial off-the-shelf (COTS) hardware. While building a lot of custom hardware might be more fun and perhaps a lot less expensive, it also makes it hard to maintain the sim in the future. When custom built components break down ... they can be very difficult or impossible to replace. So, at the current we are looking at using the following COTS technologies:

• Digital I/O -- Phoenix Contact Interbus (old, but very very reliable and trusted)
• Analog I/O -- National Instruments DAQ Equipment and Phoenix Contact Interbus 
• ARINC 429 -- V1 Avionics Simulator Interface 

Again, the key is to use as much off-the-self and easy to replace hardware as possible. 

L-1011 - CPT - DC Power Planning - Part 2

Phoenix Contact 24VDC Power Supply

Some of the components for the first DC Power Bus have arrived. To re-create the DC and AC power systems of the Lockheed L-1011 I am going to use components made by Phoenix Contact. All the elements are made to mount on standard DIN Rails and are industrial grade. The DIN Rails can be installed in the simulator very easily and create a clean setup that is easy to service. Here is an example of a power distribution installed into the overhead panel of our MD-83 simulator.

Phoenix Contact Power Distribution installed in Simulator

Two postings ago I showed you a proposed layout for one of the DC buses the the Phoenix Contact elements shown in this posting will be used to implement it.

L-1011 DC Power Bus Simulation with Phoenix Contact Components

The 120VAC 60Hz to 24VDC 10A power supply is shown in the image at the top of this posting. Each of the DC power buses simulated will receive one of them.

The image below shows the Phoenix Contact 24VDC Relays. These relays are capable of directly interfacing with many of the switches on the L-1011 simulator panels. The relay can drive all the voltages used on the L-1011 simulator including the TTL interfaces to the computers.

Phoenix Contact 24VDC Relays

The relay modules are very thin (the fill one DIN Rail slot each) and the seven relays in the image above are just 1 1/3" (about 44mm) wide. The actual relays are very easily replaced (see image below) by simply popping them out and putting in a new one.

Phoenix Contact 24VDC Relay Module

The Diode module has 4 diodes in it. Enough to protect each of the DC power supplies from voltage coming in from the DC Tie Bus. You can see the module a bit closer up in the image below together with one of the standard terminal blocks used to connect other DC components and breakers to the DC bus.

Phoenix Contact Diode Module and Terminal Block