BOEING 737NG EFIS PANEL

Knowing the panel dimensions, we are ready to design our EFIS (Electronic Flight Instrument System) panel. But, what is each button for? To know this, nothing better than an original Boeing 737 manual (you can find it in the net). Studying it, we can know the specific function for each real switch, button...

For our EFIS:

Element Qty. Notes

Paint - RAL 7043

Push buttons 11 Omrom B3F-1055

Rotaries (*) 4two simples and two doubles. 12 positions, 1 circuit, break before make.

Encoders 2 CTS-288

ON-OFF-ON switches 2 installation diameter 6,5 mm.

Screwed bar 1 M3 stainless steel

We know now what we need to buy, so we are going to look for it:

Panel: I'm going to use 3 mm. thickness white metacrylate for the seen panel and the same but transparent for the rear panels.

Buttons: it is very difficult (and expensive too) to find buttons with the same looking as the real ones, so I've decided to build them like I'm going to do with the panel. The component will be a PCB mounting key (Omron B3F-1055) and the part we will touch will be made with white metacrylate, but this time with 5 mm. thickness. We will see later how to transfer the movement to the key.

Rotary switches:

the single ones will be made with standard 12 positions rotary switches. the double ones will be made with one 12 positions rotary switch and one encoder. I'll modify the shafts in every rotary switch.

Three positions switches: really easy to find them.

 

Graphic design.

As I said before, my EFIS panel consists on several layers.

I'm going to engrave and cut the panels with a CO2 laser engraving machine. The software of the driller imports Corel Draw format files, so I will use this software to make the design.

Here is the final result (from front to back):

Methacrylate preparation.

We will start with the front panel which is made with white methacrylate. We will paint it with RAL 7043 grey color.

I'll paint the panel with an air compressor. Paint must be plastic special type. The reference I've used is Eurotex BESA-POL MATT RAL-7043 without catalyser.

When the paint is dry, we check if the light doesn't pass through it. If it's needed, we apply an additional layer.

The proccess is the same for the buttons, but we will use black paint instead.

And that's all. We can take our drawings and panels and go to the workshop to put them on the laser machine.

 

Building the panels.

Not much to say about this. We put the panels on the machine and it starts engraving and cutting. This is what we obtain::

Glueing the two pieces that form each key we have:

As you can see, the edges are whitout paint after the cutting process and the light will scape so we have to fix this problem. There are two possibilities:

paint after cutting, then engrave the text (two travels to the workshop and a very fine position adjusting of the panel in the machine).

paint the edges with a paintbrush (it's what I've done). It's not neccessary to paint the holes that correspond with the knobs, because they will cover the light. The first picture shows the correct paint method to avoid drops on the front side of the panel.

   

We can use a blade to take out all the extra paint on the rear side of the panel:

Once painted, the final result is:

The following step is to build the PCB where the backlighting leds will be fitted.

 

Backlighting PCB.

I'm going to use white high-efficiency leds for backlighting. The mean values for this type of leds are the following:

voltage drop through led: 3,3 voltis aprox. current through led: 15-20 mA aprox.

I'll use 24 leds for the EFIS. Power source will be 12 volts. I'll group the leds in 8 groups of 3 units in serial connection (leds can't be connected in parallel because when they reach the final working temperature, there will exist variations of intensity among them, causing different light intensities or leds destruction). So I'll calculate now the resistor to install in each group of 3. The circuit would be this one:

We can calculate R with the Ohm's law:

The result is R=100 ohms.

Current through the led will be 20 mA, so the resistor must reach this power:

W>VR x I=0,02 Watts

so we will use a 0,25 W resistor.

Now we design the PCB layout using any design software (Corel Draw 12 in this case):

The rest of the process is shown here.

The final result is:

 

We will connect this circuit with the one corresponding to the besides panel (MCP). This is why we have to install two filtering condensers. This way, and using the control circuit developed by Jose Luis Muñoz, we will be able to control several panel backlighting with only one knob.

 

PCB for components.

Now we are going to build a PCB for the components. This way we will minimize the number of cables and the possibility of fails due to bad connections. The components used in the EFIS panels are:

I'm going to use Corel in the same way I did with the backlighting PCB:

We build the PCB as we did before:

 

Panel assembly.

First step is fixing the switchs on the auxiliary panel:

and then fix this panel to the front one at a convenient distance, using 3 mm. diametre screwed bar:

On the visible side we will have four nuts that we will paint grey. On the rear side we will install a Grover washer to avoid nut movements. Now I'll take out the font panel to avoid scratches on it:

Next step is to install the rotary switches on the backlighting PCB:

As you can see, the rotary have been modified. The shafts have been substituted by 6 mm. diameter tube and one detent have been removed in two of them. We fix this PCB at a convenient distance:

Now, the PCBs where keyswitches, encoders and connectors are installed. Before placing the encoders, we drill a little hole in the shaft as you can see in the picture:

Now we will install the encoders shafts. We cut a piece of 4 mm. pipe at a conveniet lenght. We drill a little hole in one side. Putting this piece into position, we tie it to the encoder and put some glue to avoid play between them (both shafts must be well centered).

Before placing the front panel and the keys, we cut some wood pieces to connect the keys with the keyswitches. Then we place the keys putting some glue to avoid play again.

The final look of the panel is (move the mouse over the pictures to see different light conditions):

Last step is placing the knobs.