building the opencockpits nav radio

The NAV panel comprises a front plate laser cut and ready for backlighting, backplate, 2 x switch mounting plates and buttons.

 

 

In addition you will need the following to complete the NAV radio:

• 2 x OMROM B3F 4050 keyswitches
• 10 x 7-segment display digits
• 1 x CTS288 rotary encoder
• 2 x PCB’s for 5 digit display
• 1 x Gray knob
• 1 x Opencockpits Display Card
• Lots of multipin plugs and cables
• Plenty of time and patience
• Coffee, wine, beer or a mix of all

NOTE: The 7-segment displays need to be the Common Cathode variety and all are available from the Opencockpits Shop

Other options you might consider are:

• Dual concentric rotary encoder or alternatively use two rotary encoders to achieve High & Low digit selection (this is what I did).

• 3mm White LED’s for backlighting. (Installation details at the end of this document)

 

The Transfer and Comm Test buttons come in two pieces.  Simply glue the black button onto the clear base with superglue. The backing plate is clear to allow light through when backlit.

 

 

Here's the result. It will only take a few minutes using superglue. Edges need to be painted black to avoid light leakage when backlit. Use acrylic paint available from any craft shop.

 

 

Then some sort of pins need to be installed that will push on the switch mounted above it. I used plastic knitting needles cut to size and glued in place. Be sure to get the length correct. The pointed ends insert into the small hole in the Omron momentary switch for button centering.

 

Buttons fit into the backplate and 25mm threaded standoff shafts hold the frontplate to the back and the switches above the buttons as can be seen in the next photo.

These photos show the COMM panel but the principle is the same for all panels.

 

Glue the Omron switches onto the clear mounting plate and align with the needle ends.

 

 

 

Here you can clearly see how the needle ends insert into the switches and stop them flailing about.

 

 

 

Encoders come with long shafts that need to be cutdown. Measure the required length which will depend on your choice of knob.

 

 

 

Cut with a hacksaw.

These encoders available from Opencockpits incorporate a pushbutton switch. The 3 top legs are for the encoder (known as “A”, “C” & “B” legs) and the 2 bottom legs are for the pushbutton. The outer “A” & “B” legs of the encoder connect to two consecutive inputs of the Mastercard and the centre “C” leg connects to the corresponding Ground.

For my radio two encoders provide high and low digit selection. You may choose to use the more authentic dual concentric encoder or a single encoder with the encoder’s pushbutton alternating between High & Low selection.

 

NOTE: Pushbutton selection of high and low selection is done within the code of SIOC. Search the Opencockpits forum for example code to achieve this.

Now  onto the heart of the system, the displays board. The Opencockpits display board controls up to 16 x 7-segment displays connected as shown in this diagram. The displays PCB caters for all the associated connections to the card via multipin cables that you will need to make.

More on that later

As you can see from the picture above, the 7-segments of each display PCB connects to the board via a 7pin connector and you may have to connect several 7 pin connectors to one board. Some use splitter cables but I decided to take a pcb approach and solder a mulitpin board to the card using strip veroboard.

The Common Cathodes connect to the pins numbered 0 – 15

 

Only takes a few minutes and provides easier multipin connection.

 

 

 

Standard pcb pins were used but due to the need to push them through from the underside I modified them by pushing the plastic support down to the base of the pins.

 

 

Here you can see the rows of pins inserted from the underside of the veroboard.

 

 

 

Now onto the construction of the 7-segment displays. Again always use the mounting PCB's. They only cost a few dollars each and make it a breeze to install.

 

 

Place the displays onto the PCB’s then mount the backplate over the displays prior to soldering. Turn the whole lot over and solder the displays onto the PCB's while mounted in the backplate. This will allow the displays to more easily insert through the backplate later on during final assembly. These backplates are laser cut to very fine tolerance and if you solder without doing this you'll end up needing to file the backplate holes to fit the displays. (This photo shows the comm panel but the principle is the same).

This is the rear of the 6 digit display card. The black mark indicates which display has the decimal point.

Make sure you place the 7-segs onto the front of the PCB and solder to the rear. The front is indicated by the Opencockpits logo and writing.

NOTE: You will only need to solder pins 2(f), 3(g), 4(e), 5(d), 6(GND), 8(c), 9(b), 10(a). Pin 7 is the decimal point and will need a separate wire connecting to a Mastercard output. Pin 1 can be left unsoldered as it’s just another Ground pin.

Solder connection pins onto the rear of the PCB to provide multipin connectors. The top row of 7 pins are for the 7 segments of each display (a,b,c,d,e,f,g,GND) and the 6 pins to the left are for the common cathode of each display. In this case there are 6. The 5 display PCB will have 5 pins and the 3 display PCB has 3. Clever hey!

Secure your completed displays PCB’s onto your panel with hot glue at each corner

HOT TIP! To connect the Decimal Point (pin #7) wire it to a spare output of the Mastercard but don’t connect a GND cable from the display to the output card. The output will utilize the display card GND and therefore its own buffering and you won’t need a resistor in circuit. The DP will also be the same brightness as the other digits. I connected both Stby & Act DP's to a single Mastercard output.

NOTE: Some builders advocate hard wiring the first digit (#1) to a Mastercard output as it never changes, however Nico Kaan recommends wiring as a fully operational digit driven from the display card. The has the advantage of complete control over the digit via SIOC therefore allowing display dimming and full display testing by writing “8” to the display when pressing the Test switch. This approach does consume one extra display card output per frequency; however it also offers greater flexibility. It also simplifies soldering and you don’t have to cut the circuit tracks in order to isolate the first digit which you need to do if you hard wire it.

 

Your next major work is making up cables to connect your displays to your boards. I highly recommend making up multipin connectors. Don't try soldering directly to the display pins. Whatever method you end up using you will have a lot of pin connections to make, it's unavoidable!! As you can see the 7-segment cables can be paralleled together but the Cathode connections need separate cables to connect to their respective pins on the display board. One NAV radio consists of 10 digits so you’ll need one display board.

HERE is a circuit diagram of my complete pedestal setup.
 

NOTE: If you intend building multiple units as I did you will need to decide which displays connect to which board, remembering there is a maximum of 16 displays per board. This will dictate how many cables you’ll need and how many 7-segment cables can be paralleled together. The cable lengths will also be dependent upon where your display boards are located in relation to the radio, but I would strongly advise making them longer than expected to allow for ease of access. If you end up building a complete pedestal setup you’ll have a lot of cables to contend with.

The digital displays look more aesthetically appealing with a coloured lens over them. I used standard red cellophane sandwiched between the front and back plates and it works well.

 

 

The only criticism I have is that it’s a little flimsy and prone to tearing but if you take care it is very cheap and easy and quite effective.

 

 

Cut two strips about 50mm x 100mm.

 

 

 

 

And fold into 3.

 

 

 

 

Use very thin double sided tape to stick the celophane in place. You should be able to get this tape at office stationary stores. Don't use the foam style double sided mounting tape, it's far too thick.

 

 

And here is the result. One advantage of celophane is that it is very thin and doesn't provide too much bulk between the front and back plates.

 

 

backlighting

You may already have a preference for backlighting but I found after my own research and testing that I preferred the whiter glow and lower current draw of LED's.  I used 3mm White LED’s with a brightness of 15000mcd purchased on ebay from China. These are VERY bright and I could easily have gone for a lower brightness, therefore I would recommend something around 10000mcd. You can even go for the warm white variety if you prefer the warmer look similar to incandescent globes. There’s nothing fancy about this method and therefore it can be applied simply and cheaply by anyone with the most meagre of skills.

I’m driving my backlighting from a 12v DC power supply and connecting them in a series configuration. The maximum number of these LED’s that can be driven from 12v in series is 3, so most of my LED's are grouped this way along with a resistor. These LED’s have a working voltage of 3.4v and current draw of 20mA which results in a resistor requirement of 100 ohms per 3 LED’s.

NOTE: Take a look at http://led.linear1.org/led.wiz for a very useful LED array resistor calculator. Also be sure to connect the LED’s with the correct polarity i.e. -ve leg of one LED to the +ve leg of the next and so on. The resistor can be connected to either the -ve or +ve end of the array but for convention stick with one end throughout your arrays. I connected my resistors to the –ve end of all arrays.

Drill 3mm holes in the backplate to mount the LED’s. Use the front plate as a guide to mark the position of the holes depending on where the writing is that you want to backlight. Again I'm using the Nav panel to demonstrate but the principle is the same for all panels only the hole locations will differ.

 

Place the LED's in the holes and adjust for correct placement then use hot glue to hold them in place. Try to group –ve and +ve ends in close proximity as it will be easier to connect them together later.

 

 

Use heatshrink to protect resistor legs and other wires that you don't want contacting.

 

 

 

Now join all -ve ends of each LED group together and all +ve ends. Your 12v supply connects to the respective -ve & +ve legs of the completed circuit. I used a piece of strip veroboard and PCB pins to connect my power supply to.

 

And here is the result. Not bad hey?

 

 

 

 

The final process of getting the radio working is programming the operations in SIOC. I’m not going into detail here about this process but I would point you to Nico Kaan’s website at http://www.lekseecon.nl/sioc.html for an explanation of this very powerful software.

You can also download my file HERE. Copy this text into a notepad file then change the input/output and display digit numbering to comply with your hardware and import into SIOC. 

Weblinks List:

• http://www.opencockpits.com/catalog/index.php
• http://www.opencockpits.com/
• http://personales.ya.com/micabina737/indexi.htm.

• http://www.lekseecon.nl/
• http://led.linear1.org/led.wiz

DISCLAIMER: Please use the instructions in this tutorial at your own risk. The author claims no responsibility for hardware or electrical damage as a result. This tutorial is made available as a guide only and represents the process, views and opinions of the author and not of Opencockpits or any affiliates.