Hello from a very inexperienced builder

[ame]

Ame,
I would agree with most of what you posted but...

I agree with most of what I said, but I apologise for the tone being slightly aggressive. The "simples" was intended to be ironic- I know it's not that simple. And you are right that it is often hard to get accurate information, but sometimes it seems that people don't bother to look. Or if they find it they don't bother to use it. Anyway, each to their own.

[ame]

After thinking it over all day I have decided to build the transponder. So to that end I have been looking at a small CNC machine to cut and engrave those plates and buttons. I can use it for later projects.
Rather than the Bendix King I would actually prefer to try to duplicate the Appareo Stratus ESG
https://sarasotaavionics.com/avionics/stratus-esg
although without all the functionality.

Ah, so what you are saying is it's a thinly veiled excuse to buy more tools! Excellent.

A CNC might be cool for this, or a 3D printer. Why not buy both? And a laser cutter.

Seriously though, the brochure has a nice drawing of the fascia, with some dimensions. You could print that and then measure and scale the other parts, such as the switch actuator sizes and location, the display aperture, and the depth of the bezel.

A quick search of AliExpress shows me that OLED display modules of about the right size exist. Your aperture might mask part of the display, but that's fine.

Here is one claiming to be 2.8" (diagonal measurement):
https://m.aliexpress.com/item/4001069730662.html

This one claims to be 3.12", but it looks the same, and 3.12" seems to be a more common designation. You probably want a blue one:
https://m.aliexpress.com/item/4001175707043.html

This one has a very poor diagram with it too:
https://m.aliexpress.com/item/32949282762.html

It claims a 66x16mm active area, which fits in with my crude estimate of 70x20mm looking at the PDF. It would be worth finding a clearer dimensioned drawing of the module, if that's what you're going to use.

And some buttons.

Are the buttons backlit?

[ame]

Ok, I printed the PDF to get some measurements, and zoomed in on just the fascia. My scaled measurements for the display aperture are 71.14 mm by 19.3 mm (my initial estimate was done by measuring the image on my phone screen).

Again, these are nominal, but a well-known OLED manufacturer makes a 2.8" OLED module and a 3.12" module.
2.8: https://www.winstar.com.tw/products/oled-module/graphic-oled-display/oled-256x64.html
3.12: https://www.winstar.com.tw/products/oled-module/graphic-oled-display/3_12-oled.html

The 2.8" display has a Viewing Area (the glass surface within the metal frame) of 71.104mm by 19.264mm, so that's what I would probably go for. The Active Area (the bit that lights up within the glass area) is a little smaller, so that would be fine.
Here's another one: https://www.aliexpress.com/item/4000207660366.html

The 3.12" display is a little larger than the aperture in the drawing, so probably it's not what you want. Worth double-checking everything though. Especially worth checking what you are ordering from AliExpress. These two modules do exist, and they look very similar in construction and very similar in size, but they are just different enough to annoy you.

When I draw stuff I do everything in metric, but I am well aware that in a lot of cases the original design was done in inches. So I will measure stuff in mm, calculate the nearest imperial multiple, and annotate my drawing in inches. Then I will mix mm and inches in my CAD drawings (makes sense when you see them...). As well as considering that the original design is in inches I also note that the measurements chosen are usually 'nice' numbers like 1/8", 1/4", 3/32", etc., so if I am scaling a photograph, for example, I will 'nudge' my measurements to the nearest nice number in inches.

In the case of this transponder, although the measurements of the front panel are given as 1.69" x 6.38" (43 x 162 mm) I suspect they are actually 1-11/16" x 6-3/8" or 1.6875" x 6.375" (46.86 x 161.92 mm). A 6-3/8" wide panel will fit a nice 1/8" grid (or 1/32" grid) for lining up switches and indicators.

[ame]

Finally (for now), the driver chip on the OLED display board is an SSD1322. Here's a discussion about getting a display with that chip working with Arduino:
https://forum.arduino.cc/index.php?topic=500292.0

It's a bit old, which is good news because it means that now it's been around for a while and there should be more people using it (and fewer bugs in the libraries). And if the chip can be driven from an Arduino it can be driven from any other micro you choose.

Don't worry if you don't understand the details yet. It's sufficient to know it's possible to drive that display and make it do what you want.

[Kaellis991]

For getting the dimensions Bluebeam REVU does a pretty good job on pdfs.
I do have a Makergear 3d printer. I use it with REVIT and Fusion 360 to create the models and Simplify 3D for slicing. I could do all of the plates and enclosure with that process, but I like the idea of using cast acrylic for the engraving of the lettering. No backlighting is required.
I dont know any other way to create the small lettering but with laser engraving. Not too easy to create the lettering with a 3D printer. Of course the transponder unit could be functional without all the button labels. Or go the cheap route and just paste on some labels.
There is a company about 4 hours from me that can do all of the acrylic cutting and laser engraving including materials for around $120.00. But I am still wondering if I should put that money into the CNC router and laser engraver for future sim projects.

Along with the CNC router I am looking at there is a laser option that is available. So far what I am reading is that it will do the job for about the same cost as that Flight illusions transponder with controller board.

Those OLED displays look promising, but couldn't I just use the same 8 digit 7 segment display it I were to build the Status?

Still mulling it over....

[Joe Lavery]

Kirk,

Be careful with the CNC machines that offer a laser option, they are fairly low power devices only really suitable for engraving.
The K40 lasers sold on eBay are about as basic as it gets, but for the price, I've seen some amazing work done with them.
For panel making the laser would be my first choice, becasue it's quicker than CNC and doesn't make as much mess. Having said that, cutting acrylic does produce some nasty smelling fumes.

CNC is good for larger stuff and particularly if you want to backlight you panels like the pro's do. Yet making small items on a CNC can be challenging becasue you have to devise methods of holding them while cutting.
If you want to see how that's done have a look at Mickey's Flight Deck on YouTube, he's managed to produce some small components using tabs and superglue.

https://youtu.be/CLfqXX-MukM?t=455

Joe.

[Kaellis991]

Kirk,

Be careful with the CNC machines that offer a laser option, they are fairly low power devices only really suitable for engraving.
The K40 lasers sold on eBay are about as basic as it gets, but for the price, I've seen some amazing work done with them.
For panel making the laser would be my first choice, becasue it's quicker than CNC and doesn't make as much mess. Having said that, cutting acrylic does produce some nasty smelling fumes.

CNC is good for larger stuff and particularly if you want to backlight you panels like the pro's do. Yet making small items on a CNC can be challenging becasue you have to devise methods of holding them while cutting.
If you want to see how that's done have a look at Mickey's Flight Deck on YouTube, he's managed to produce some small components using tabs and superglue.

https://youtu.be/CLfqXX-MukM?t=455

Joe.

The idea is to cut the 3/16" acrylic with an single spiral open flute bit. Cast acrylic is the better material for doing that. Feed rate and spindle speed would have to be dialed in. Then paint the acrylic black and use the laser to remove the paint to expose the white acrylic below. No need for any backlighting, just want the professional looking text. The text is the main reason for purchasing the laser engraving option.
I have looked at Mickeys's videos and was very intrigued by the CNC machine he built from plans he purchased. Looks like that would be a challenge but fun, however, I priced out all of the components and it's a bit more than I can justify spending. Some of those rails and guides are expensive.
Yes, one good way of holding pieces is to use blue tape on the table and on the piece and then gluing the tape together with the 2p-10 adhesive (i.e. superglue). I think each of the (3) plates can be cut from one larger sheet that's clamped down if need be. The CNC table has slots for clamps. There will be some waste. The buttons will be printed on my 3D printer, in white PLA or PETG, sanded then painted then secured to the router table and engraved with the numbers. That will take some careful alignment. That's the plan anyway...
The mechanical aspects of this build are the easy part for me....the electronics are the challenge right now.

[Joe Lavery]

You seem to have a good handle on what you need to get the job done. But cast acrylic can be tricky to machine, because like aluminium it likes to stick to your cutter, so the correct feeds and speeds are very important.
I broke a whole range of cutters until I joined CNCZone.com, like this forum there are lots of knowledgable folk ready to offer advice and help; just ask the questions but make sure you use the search facility first; you can bet someone has already asked the question before.   

Good luck! 

[Kaellis991]

You seem to have a good handle on what you need to get the job done. But cast acrylic can be tricky to machine, because like aluminium it likes to stick to your cutter, so the correct feeds and speeds are very important.
I broke a whole range of cutters until I joined CNCZone.com, like this forum there are lots of knowledgable folk ready to offer advice and help; just ask the questions but make sure you use the search facility first; you can bet someone has already asked the question before.   

Good luck! 

Looks like a good resource. Thanks for the heads up.

[ame]

For getting the dimensions Bluebeam REVU does a pretty good job on pdfs.
I do have a Makergear 3d printer. I use it with REVIT and Fusion 360 to create the models and Simplify 3D for slicing. I could do all of the plates and enclosure with that process, but I like the idea of using cast acrylic for the engraving of the lettering. No backlighting is required.
I dont know any other way to create the small lettering but with laser engraving. Not too easy to create the lettering with a 3D printer. Of course the transponder unit could be functional without all the button labels. Or go the cheap route and just paste on some labels.
There is a company about 4 hours from me that can do all of the acrylic cutting and laser engraving including materials for around $120.00. But I am still wondering if I should put that money into the CNC router and laser engraver for future sim projects.

Along with the CNC router I am looking at there is a laser option that is available. So far what I am reading is that it will do the job for about the same cost as that Flight illusions transponder with controller board.

Those OLED displays look promising, but couldn't I just use the same 8 digit 7 segment display it I were to build the Status?

Still mulling it over....

Hello again,

You seem to have identified the kinds of problems you're going to have to deal with. To be honest it's a bunch of practical problems that need practical solutions, and you are already assessing what's going to work and what is not. For example, 3D printed text does indeed look awful, but cutting with a CNC or etching with a laser brings along their own set of problems.

You said you are considering the Stratus because "WIthout the rotary encoder to change modes perhaps a little simpler?". I disagree. The switch on the KT76C is not a rotary encoder. It is a 5-position rotary switch, and it is easy to hook up to a micro. Also, if you use the 7-segment display on the Stratus it won't look like a Stratus. It will look like some random display and a bunch of switches, just like the Propwash offering.

Since you started discussing your project in an open forum I hope you don't mind people questioning your decisions. I'm happy to help if I can, but also not averse to stating my opinion, although I will try to justify it- I am not being negative for the sake of it.

Anyway, it's a noble goal, and definitely achievable. One of the things you can take advantage of, because you are building it yourself, is incremental improvement. The off-the-shelf solution is final. It has to be complete and working, and looking good. Your version could have ugly 3D printed buttons at first until you figure out a better solution. Then, because you made it, you can easily dismantle the unit and re-assemble with nicer buttons, for example. Or build another one. Or you could get the unit running on a breadboard on the bench, and figure out the enclosure later, or in parallel with getting the hardware and software working.

[Kaellis991]

What I will probably do is just make all the housing and faceplate components on my 3d printer without the fancy lettering as a proof of concept design. Once it is working I will decide whether to purchase a CNC router with a laser head or just outsource the cutting and engraving of the acrylic as a way of getting the text and numerals on the buttons and faceplate.
If the rotary switch is easier then I will probably just go that route. Besides that switch was ordered a couple of weeks ago and will be delivered mid October. So based on your good advice about the switch I think I will just continue down my original path with Bendix/King. Thanks for the input...

[ame]

Ok. No worries.

The DIY Bendix used a 30 degree switch, but the real thing has a 45 degree switch. Electrically they are identical, but the labels for the switch positions are in different places. Anyway, when you have done one you'll have all the skills to build another.

Incidentally, I modelled the Stratus in OpenSCAD for a lark (don't use/like/want Fusion). Attached is a rendering without the switch actuators. I'm sure the 2.8" OLED is the right one, so if you decide to take it further (or anyone else reading this) then I'm sure the parts are available and a representative copy can be made.

[sagrada737]

Hey Kirk,

I have been watching this thread progress, and I see it starting to lean toward machining/engraving.  Those are certainly interesting topics, but I thought you were interested in making/or buying a Transponder for your current Sim.

I would like to offer a suggestion to perhaps help you focus on getting where you want to go with the Transponder project. 

1.  Create a specification for your Transponder requirements. 
2.  Decide if you want to design your own Transponder module to match your specifications; or buy a Transponder module that meets or comes close to your specifications.
3.  Having settled on the direction you want to go.  Freeze your decision/design. 
3A. If is to buy a Transponder module, then buy it, use it in your Sim, then decide how well it meets your requirements. 
3B.  If it is to design your own Transponder, then you must proceed in a systematic manner.

Designing your own KT-76C Transponder will consist of electrical/mechanical/software considerations in order to meet your specifications.  Consider the following guidelines:

Electrical: 
1. Create a schematic that details ALL the electrical connections, components, layout, and interface.
2. BreadBoard/Prototype the electronics and test its basic electrical operation.

Software:
3. Design and create test software to further test electrical operation, eg. switches, display, etc.  When all meets your specification, then finalize the electrical design.
4. Create a software specification that represents the operations functions of the Transponder that meets your baseline specification.
5. Select the hardware/software methods you will use to interface/program the Transponder functions.
6. Design/program the first level software code to accomplish an "active interface" that allows you to exercise your electronics prototype module, eg. switches, display, etc.
7. Design/program the second level code that actively interfaces with your Sim software, eg. XPlane, P3D, etc.  Confirm that both the Sim and your Transponder software communicates (reads/writes) with each other.
8.  Refine/Debug your software code to accomplish a functional Transponder operation that meets your specification, then finalize the software design.

Hardware:
When your are satisfied with the electrical operation, and the software operation, whereby it meets your electrical/software specifications, then you can proceed to packaging your module to meet the mechanical specification for Form, Fit, and Function.

At this point, you have a real-world representation of what a KT-76 Transponder looks like, and its dimensional characteristics.  With that information, you can decide how best to "duplicate" the KT-76 into something that meets your mechanical specification for your Sim, that is realistic for you to build/machine/fabricate.

Building your own KT-76C Transponder could be a wonderful challenge, but be careful not to get the "cart before the horse".  Lots of different approaches to the above.  These are simply a few considerations for you.

Also...  Be careful in justifying/buying support equipment/machines simply to do some one-time machining on a Transponder project.  Keep in mind that any technology has learning curves associated with it.  Remember that CNC machines like 3D printers, milling machines, lathes, engravers (laser/mechanical)...  ALL require a significant learning curves and levels of expertise in order to use them for useful work, to make useful parts.  Don't forget that CAD/CAM/Post-Processing software expertise is needed for all these machining solutions.  It is easy to spend thousands of dollars on machining solutions, only to get bogged down in the machining solutions, even before you make one single useful part.  All machines have tolerance issues associated with them.  3D printing is by far the worse, as the design needs to allow for the limitations of the 3D printing process/materials.  CNC milling/engraving is wonderful, but it too has tolerance issues, and related issues having to do with the material to be machined.  Engraving text with a fluted tool is challenge, requiring very high accuracy and very high RPM.  High quality engraving tools are expensive.  The cheap ones don't do the job.  Laser engraving has challenges as well.  The accuracy and control of the Laser head greatly affects the quality of the finished result.  Cheap laser engravers give you the quality that you paid for.    On and on...

Listen...  I'm not trying to burst your bubble, or tell you how to do your projects.    I'm just speaking from experience concerning some of what you have posted.  I have all the capabilities in my home shop spoken of above.  I got rid of the low cost laser engraving, as it was unreliable.  The key thing to keep in mind, is that it's important to "discern the total cost" of whether to Build or Buy.

That said, this is a hobby, and the challenge of building your own KT-76C Transponder, no matter the time or cost, can be very rewarding.  Nothing quite like building your own stuff!!!

Best wishes on your project.

Mike

[bernard S]

okay my two cents     

Up down faster slower turn stop  and look out window   that is primary goal and should always be working... because you can go down a dark path of always building and missing the primary objective which is to fly

then control loading after control loading comms

then do  whatever else takes your fancy