L-1011 Trainer Installation: Radio Head Cabling - ARINC 429 Prep

L-1011 Trainer - Radio ARINC 429 Cabling

The picture above is a good illustration of what most of the build sessions over the last few weeks have looked like. While there is lots of good progress, they are hard to really blog about. However, what you see in the image above is cabling work done on the Center Panel. The panel is home to the communication radios, the #3 INU CDU and the audio panels. There is also a controller for ATC as well the radar controller. The radios had been cabled to 24V DC and 440Hz 110V AC power a few weeks ago, however last night we installed the cabling for the ARINC 429 connections that will read data from the instruments and also send data to the displays. 

Avionics Bending: Gables Radio Head Operation

I thought I should add a short video on the fully connected radio head. I realized that just showing still images in the previous avionics bending blog entry didn't really show you how it actually worked.

Below is an image with my test setup using my iPad to monitor the ARINC 429 traffic coming from the Gables head. (Note: There is no direct connection between the instrument and my iPad ... the data is captured on a Linux system and the iPad just shows me the numbers via a network connection ... however, it would be really neat to have an iPad app to do ARINC 429 stream debug with).

Avionics Bending: Gables Digitial Radio Controller (ARINC 429)

I found these really cool radio heads made by Gables Engineering in Florida. The heads I have originally flew on a FEDEX MD-11, however, they could of course have also been fit into a later model L-1011. Therefore, I think they will work just fine for the project. What makes them even more interesting is that they use the ARINC 429 protocol. I have been working with ARINC quite a bit lately and so this is my first step into hooking this ARINC device up to X-Plane. Here is a more detailed description of the individual components of this Gables unit:

1. ACTIVE WINDOW - Displays the active frequency and selected radio. Displays ACARS in one of the windows for VHF-3. Displays FAIL in both windows in case of CRP failure.
   
2. TRANSFER BUTTON - Push to transfer the STBY frequency to the ACTIVE window for transmission. STBY frequencies cannot be transmitted until transferred to ACTIVE window.
3. STBY WINDOW - Displays the standby frequency and selected radio
4. FREQUENCY SELECTOR - Turn knobs to select frequency in STBY window only.
5. Push to select respective radio. Selected radio is displayed in the STBY/ACTIVE windows.
   

The first image in the blog shows the radio head selected for VHF 1. The VHF 1 information is transmitted as ARINC 429 Label 030. The data in the 32bit word is BCD. All 3 VHF radios are controlled with the same ARINC 429 label however, each VHF radio uses a different SID. The VHF1 radio is addressed with the SID set to 1.

Below is the radio selected to the VHF2 radio. Again the Label used is 030. However, the VHF 2 radio has a SID of 2.


Finally, the 3rd VHF radio (VHF 3 ) is use transmitted as Label 030 with the SID set to 3. The BCD format for the Label 030 uses bits 29-11. The digit "1" ad the beginning is not transmitted since all VHF frequencies used for communication start with a "1".


Next is a in image of what the data looks like on the computer once the ARINC 429 information has been decoded and readied to to be handed over to X-Plane.


The image above shows the 3 VHF radios on the right and the two HF radios on the left. The VHF radios are shown as VHF1, VHF2 and VHF3 from the top down. The two HF radios in the screen shot do not show the frequency because the decoder in both cases showed the second 32 it word that makes up the HF word.

The image below shows the radio set to HF1. The HF information is transmitted as ARINC 429 Label 205 for the new style HF encoding as well as the ARINC 429 label 207 for the HF status word. Label 205 transmits as two 32 bit words ... the first word holding BCD data of the first 5 digits and the 2nd word has the BCD data for the 6th digit.


Below is the radio set to HF2, again here the two HF radios are encoded using the SID of the ARINC 429 word. SID of 1 is for HF1 and a SID of 2 is for the second HF radio.


In order to make this work I used a DDC ARINC 429 adapter card. I don't have the right connector for the radio head yet, so I build a temporary cabling setup. The radio had has one TX and two RX channels. For this example, I only cabled one RX and the TX channel. The RX channels are used to synchronize multiple radio heads in the cockpit.


Unlike many other radio heads, this head actually works of 28V DC power and not the 110V 400Hz AC power that I normally use. Therefore, I hooked the entire head up to small power supply proving me with 26V DC as well as 5V DC for the instrument lighting.


The next picture shows the complete setup. The DDC ARINC card has a DB37 output, and I use a DB37 breakout board from DAQstuff.com to give me easy access to the RX and TX channels on the card.


I am not using 85Ω twinax-cable quite yet for the ARINC 429 connections, however, the distances on this test setup are so short that the channels work fine without 85Ω termination.


Gables makes some really awesome equipment and they are a super cool company to interact with!

Avionics Bending: Incandescent Replacement - Radio Heads

The original incandescent light bulbs give the light plates and the digit drums a yellow tint. Especially on older light plates, the entire legend turns to a rather hard to read yellow. Bright White LEDs are normally calibrated for 5200K (daylight) and will help quite a bit with the faded instruments.

In the image above and the below, the radio had that has been re-worked from incandescent to LEDs is the one on the left and on the bottom respectively.


Removing all the original lighting and replacing it with LEDs is quite labor intensive ... it takes about a two days to work a single radio head ... but the results are awesome.

Avionics Bending: VHF COMM Radio Head (Prototyping)

Last week, I posted the Design Specifications for the Radio Head interface for the Lockheed L-1011 project. Today, I built the prototype for the USB Attachment Unit (AU) based on the ATMEL ATmega32U4 micro controller. The I/O element used for the prototype is a MCP23016.

I have not modified the diode plate in the actual radio head quite yet, but as you can see in the image below, I have attached temporary connections from the radio head to the proto-board.



The layout is rather simple, as can be ween below. I will post the software for the project once the final board has been designed.



You can watch a short video clip below to see the radio head in action. Currently, the AU data is simply dumped to the MAC reading the USB output (the integration into X-Plane, as described in the Design Specification, will follow next week).

Design Specification: VHF COM/NAV Frequency Selector

I have written a design specification for the VHF NAV and VHF COM frequency selectors used on the Lockheed L-1011 Project. I call them "radio heads". I would like to get some input on the design document. You can see the document by following the link below:

Radio Head Design Specification

The electronics components selected for this initial design specification are the ATMEL 8bit ATmega32U4 MCU and a I2C controlled I/O chip made by NXT.

Avionics Bending: VHF COM Frequency Selector (Analysis)

For the Lockheed L-1011 project I picked a number of VHF COMM heads made by Gables Engineering, Inc. The unit that we are taking apart in this posting was last inspected in 1989. You can see a more detailed posting about the VHF COMM head in one of my other blog postings.


The unit has a rather simple aluminum enclosure that hast two parts, a top plate and a "U" shaped casing. The top plate comes off by removing 4 screws on top.


After removing the top plate, we can see the the mechanical elements for the left and the right frequency selector as well as the diode board on the back of the unit and the frequency selector switch.


The "U" shaped case can be removed by removing four screws; two on each side of the unit. Once the screws are removed, the case will simply pull off.


Now the VHF COMM radio head can be accessed from all four sides. The next few images illustrate the various component elements:

Top View


Right Hand Side View


Bottom View

Left Hand Side View

The digit drums have their own lighting elements, there are 4 lamps for each drum. Which frequency is being sent back to the actual radio is controlled by the selector switch. The switch not only powers an indicator light above the frequency window, it also powers the respective encoder mechanism on the backside of the frequency selector.


When the toggle switch on the front of the instrument is moved to the right, the right selector is energized, and with the toggle switch thrown over to the left, the left frequency selector is energized.


All encoder signals are being fed through a number of diodes and then to the back connector of the instrument. The diodes keep the left and the right frequency selector isolated. Again, the choice which of the two frequency selectors is being used is made with the toggle switch.


Despite there being 21 diodes for each selector, the frequency of each selector is actually only encoded with 16 bits. 8 bits for the numbers on the left hand side of the decimal point and 8 bits for the digits to the right of the decimal point. For example the frequency of 118.15 and 118.17 are encoded as follows:

• 118.15 010110000011010010011
• 118.17 101100000011010010011

Original Flight Hardware: VHF COMM Radio Head

For the communications equipment on my Lockheed L-1011 project I have picked Gables Electronics radio heads. The heads are simply frequency selectors for the VHF frequency range of 118.00 MHz to 136.97 MHz.



The head uses a two drum-style digit displays that are backlit and are each driven by the respective two-element selector switch. The big rotating knob on the bottom of the two element stack controls the digits to the right of the decimal point. The smaller one on top controls the digits to the left of the decimal point.

The TFR switch points to the active frequency and renders the other one the stand-by frequency. The active frequency selection is also indicated by a green illuminated dot.


Panel Location