View Full Version : Building A GA Transponder

10-01-2009, 06:46 AM
Has anyone ever attempted to make a transponder for GA use, I would like to know what would be the easiest way to make it, as I have seen lots of different types of transponders and different ways of making them.

I am thinking of just using push buttons and a simple encoder.

Would this be wise?



10-01-2009, 10:03 AM
I haven't started yet, but plan to make one similar to this (http://www.simkits.com/product.php?prodid=228#). It will use the same led displays I am using for my Nav/Com unit. I plan to use an acrylic faceplate with graphics printed on full sheet sticker paper.

10-01-2009, 10:10 AM
Basically your making it the way that I am making my whole entire radio stack! lol :)

I have had my radio stack professionally printed on to adhesive matt vinyl which is then applied to red transparent acrylic with the displays cut out to revela the red acrylic, it looks awsom! Funny thing is that they had to print 4 of them on one piece of vinyl because the vinyl sheet was so big that they could print 4 on one sheet!

10-01-2009, 10:15 AM
By the way....if you are going to print on sticker paper, make sure that you print on decal paper with a layer of varnish and make sure that you have an exceptional quality printer and print at highest resolution. I went down this avenue, I thought that my black and white laser was exceptional, but once I printed it; it looked like I literally did print it, hence going down the professional printers route! Just google sticker printers and I am sure that they will be able to run a few of your designs off as samples to save you money!

10-01-2009, 11:07 AM
I thought your radio stack looked great. How thick is the red plastic? Is that the main panel or is there more to it? I printed the faceplate for my ASI on sticky paper using a color inkjet and it looks fantastic. The black is "blacker" then using my laser so it looks better.

10-01-2009, 12:08 PM
The picture that was on my radio stack diagram in one of your postings was not my radio, I just displayed how to get similar results by using a radio stack that is similar! The radio stack as actually photographed is an elite radio stack that costs $$$$'s of dollars, I just showed you how you can achieve this; you can create a replica of this radio by:

1) You will need to do a screen dump of an actual FS Radio stack, by this I mean you will need to copy a photographic image of the complete radio stack.

2) Next, remove the buttons /encoders and knobs etc by using a paint program like photoshop or gimp.

3) You should just have the bare panel of the full stack now!

4) Go to the printers and get them to print your image onto matt vinyl!

5) Get some 3mm (or 2mm) red transparent acrylic cut at 160mm wide by however long your stack is and cut out all the holes for the buttons, switches and encoders, then apply the vinyl image to the acrylic.

6) Get a brand new and ultra sharp scalple knife and cut out the areas that you need to display the digits, remove these areas to have just the red acrylic showing, so that when you place the digits behind the red acrylic they will show like the real thing!

7) Insert all your electonics and wire upto your I/O Cards, then mount radio stack to MIP!

Just take a screen dump from the radio stack of FS and just edit it, render the res up a bit to atleast 300dpi and that should be good enough to use unless you want to use your panels!

BTW.......I am using 3mm red transparent acrylic to do the job....


10-01-2009, 12:24 PM
look at this web :



10-01-2009, 12:36 PM
look at this web :



That site is full of good stuff, I've had it bookmarked for quite a while.

10-02-2009, 01:53 AM

I have selected a very simple design, NARCO AT 155 TSO

I have 4 pcs of CT288 encoders connected to Opencockpits master card and 4 pcs of 7-segment displays connected to Opencocpits Displays II card. Also a small ELMA rotary switch to set the mode.

On the picture i am still missing the plastic frontpanel and the knobs are just some scrap ones i found to testfly it...


10-02-2009, 06:49 AM
Hi Wriley here is the acrylic that I am using for my entire radio stack:

3mm thick red (transparent) acrylic 160mm x 296mm




10-02-2009, 10:25 AM
Hi Wriley here is the acrylic that I am using for my entire radio stack:

3mm thick red (transparent) acrylic 160mm x 296mm

Thanks Alex. I will see what I can find locally.

10-02-2009, 10:29 AM

This is what I ordered, they may even sent to the USA!

10-02-2009, 08:19 PM
Bumping up the DPI will make the image larger but not increase resolution. To do that you will need to go back in and edit the image. Pretty much what I've been doing with my MIP drawing. As it was well the resolution of the parts manual I wanted it to be much larger and more accurate (changing from 'F' to 'H')

In this instance you would need to redraw using the up sized version of the stack all the parts you are going to see when printed. You may need to do that a couple of times as it's hard to work with such a zoom factor when re-rendering the image. You may even want to take a trip to Spruce or Airliners.net or other such websites to confirm the accuracy of the radio stack just to be safe. Also remember that in the FS stacks there is a bit of 3D effect added in many times. This would have to be 'edited out' so you have only a 2D version of the stack.

Modern printers can go to 1400+ dpi. If you can remove pixelisation at 300 dpi that would be a fine resolution. Just make sure you are working with that resolution before you print. run a test print to see.

The stack itself is pretty basic 'graphically' so it wouldn't be to hard to get a high resolution version made up pretty quickly..

That said you may want a couple of prints one with all your labeling/graphics + cut/drill points (knobs/buttons/switches removed) and one with all that still in there so you know what goes where when building the other bits. Of course the latter need not be printed on the adhesive vinyl like the first..

I'm hoping to be using the Garmin systems in my simpit. Not the G1000 but the smaller units. Having a some Bendix King equipment in there would add some flavor to the cockpit though so I'll be following your build.. As with all the other things your doing hehe..

10-03-2009, 05:48 AM
Hi Ron,

My digital print specialist wanted my artwork at 300dpi. I did not use the FS stack as I thought that the quality of the image was a little too 'bitty' for my liking and needed something a little more 'upscaled'. So I just downloaded as many of the radio stack add-ons demos as I could to get the best radio stack, and one particular add-on done it for me nicely. I just took a full scaled full sized full colour screen dump and then started working on the image on a photo editing prgram, removing all the buttons, and switches, just leaving the tags, texts, lines and layout! The 3d effect will indeed work in your favor and not against. But if you have removed all the switches and buttons you will not actually be left with any 3d effects, although my radio stack is printed at unbeliveable quality, and quality that you couldnt get on a home printer no matter what printer you had. My stack is printed onto self adhesive vinyl and is printed at full colour actually matching the colours of the real radio stack. I am so happy because I have managed to recreate the entire bendix king radio stack and not just one radio, the stack is photo quality! I have 4 of these radio stack vinyl fascias printed as I got 4 printed, 1 for drilling the holes into, then 1 as the actual fascia, leaving 2 spare incase I make the 'cut of death'.

But then again I can print a load of fascias on my home printer on to paper so that I can use them for location points to drill holes etc which will save me using one of my vinyl facias (leaving 3 spare). I may even make 3 entire radio stacks just for the fun of it! (sell them to fund other parts of my project)...



10-03-2009, 10:30 AM
That was kind of my next question .. What were you going to do with the remaining vinyl printouts ??? It's good to keep some just in case you mess one up.

How much did it cost to make the vinyl printout?

I don't know if I could set up something similar with the Garmin stack. There manuals come with pretty good graphics of the components. Most of the component though is buttons.

10-03-2009, 10:55 AM
Hi, I done some sweet talking with a print company who wanted to charge me 45 for setup fee plus 15 for a meter of hi resolution printing to vinyl, but managed to just pay the 15 as I had done pretty much most of the preperation work that he was going to charge me for him doing that work.....him now not doing that work I paid just the 15, most companies will usually charge a hefty setup fee for a 1 off, many wont do a 1 off because its not worth their time unless you pay this 'setup' charge (which i cheekly manages to avoid).....

Yes I have plenty left over, but I guess I will keep them for the future, like future upgrades etc!

Its pretty cool to have a bendix king radio stack replica in the simpit, it simply looks awsom! Not many will have anything like the bendix king radio stack in their sims due to simkits charging a small fortune, so my way is definitely the best way, it may not have ALL the functions of the original radios but it sure does cut close!

The formula for a decent radio stack is definitely:

Screen dump GA Stack > Photoshop It > Print to vinyl > Add to acrylic > Add electronics > Interface.....

Definitely better than the over sized radio modules that resemble nothing like anything ever seen in a Cessna!

Just google printers in your area, and I am sure someone will do the job for you!

Good Luck....


10-03-2009, 10:58 AM
I don't know if I could set up something similar with the Garmin stack. There manuals come with pretty good graphics of the components. Most of the component though is buttons.

Your probably better off designing a hi resolution radio stack form scratch, but make sure that you use the original colours and textures to create the stack to give it the bendix king look!

10-03-2009, 05:13 PM
I have a sign maker that has a shop just a few blocks from my house. I'm not sure if staples would be willing to do something like that. I know they can do large format printing. I was going to go there for my MIP printout. It's probably a special process to print on vinyl though.

With the BK radios it's pretty easy well easier. The Garmin radios are more like car radios these days. Knobs would almost need to be made from a polymer clay or something. Needing a mold first.

- Sculpt button
- Make mold
- Form button inside mold
- release from mold
- bake
- paint

Simplify the Garmin faceplate giving up some prototype appearance in favor of ease of construction.

With the Garmin I could use the Reality XP gauges and an LCD to display them. It's integrating the controls into a thin layer that would sit in a sheet of plexi above the LCD that would also have the template added to it. There is a bit of depth between the faceplate and the actual LCD display on the Garmin units. I would guess about 1/4 inch. So I have a bit of room to play with. It would mean making a control that looks like the one on the unit but of course interface with FSX/Reality XP gauge.

I still wouldn't mind building the BK Transponder though as that often sits off on the co-pilots side of the pit and would give the simulator a bit of a vintage feel to it.

I'm watching the Garmin build here in GA aircraft and that could lead to great things when I'm in the need of a radio stack..

10-03-2009, 06:04 PM
With the BK radios it's pretty easy well easier. The Garmin radios are more like car radios these days. Knobs would almost need to be made from a polymer clay or something. Needing a mold first.

I would sure like to find a source for BK style knobs for a dual shaft encoder. All I can find is the big jet style. If I ever get my hands on the real thing (or something really close) I want to try making a mold and casting a pile of them.

10-03-2009, 08:07 PM
I'm thinking exemplar could be made out of wood. Probably go with a RTV (Room Temperature Vulcanization) mold process. Similar to epoxy you have two parts you mix and then it hardens at room temp. There is much info on the net about the process.

I'm thinking for the duel encoder you have two parts to the knob. You would need two shafts one to go inside the other. So both parts of the knob need to have a recess for the shafts to fit into. Then gears off of each one so you can actuate the change via rotary pot perhaps.

It would be great to get your hands on the knobs for mold making. You may want to take a look at this...



10-04-2009, 04:16 AM
On my bendix radios I have removed the need to use dual encoders, because unlike yourselves I am very limited to funds.

So instead of using dual encoders, I just use normal encoders with a single knob. My encoder costs 1 and the knob costs 30 pence! Compared to 15 for a dual encoder and 5 for a knob saving myself 37.40 per radio, and when you add all the radios up, there is a massive saving!

This is how I have wired mine up:

I have wired my single encoder to a toggle switch so when I have the toggle one way I am selecting GHz and when i flip the toggle the other way I am selecting MHz.....

How easy is that! and a massive saving!

Just add a standby button and your then your red digits and voila!.....your done!

Again this is a great money saving trick, I haven't got a lot of money at all, and I believe in simplicity and saving 's, and this way I am very very happy!


Geremy Britton
10-04-2009, 06:28 AM
Alex, looks great... and an excellent budget idea.
Are you planning on getting some LED digits in there or just using a screen to display that information?

10-04-2009, 06:34 AM
Hi Gez, I am indeed using digits, would hope to have the opencockpits master card and displays card by december, so just a little bit of tweeking with sioc and it should be pretty much functioning, I will have the whole radio stack finnished by this time next week, its coming along nicely!

Cheers Gez!

10-05-2009, 12:35 AM
I am selecting GHz and when i flip the toggle the other way I am selecting MHz.....

Nice work and ideas from you guys, but i am sure the frequency is Mhz and Khz.

Keep up the progress :-D

10-05-2009, 04:24 AM
but i am sure the frequency is Mhz and Khz.

You are indeed right there, that diagram was just drawn from the top my head just to show the idea, of my course my legends are correct! I can assure you of that lol!

Well spotted though!