I want to build this transponder for my flight sim but there is no info on that web page about the controller other than it is Arduino and using ArdsimX. I went to the arduino website contacts Webpage and they directed me to, yet again, join another forum to get information. Since this is the first time for me to delve into this controller board jungle, here I am. I am losing track of all the forums I have to join to try to get any help.
Can someone be so kind as to direct me to where I can find information on what controller board I could use for this project?
Regards
Kirk
One way to approach this project is to forget that it's a Bendix King KT76C Transponder and look at what the user interface is that you have to emulate.
It looks like there are:
- A number of 7-segment displays.
- 11 pushbuttons
- 1x 5 position rotary switch - effectivel another 5 pushbuttons
The author of the project has already figured out that a MAX7219 display driver (SPI device) will handle 8 7-segment digits.
You need to handle the 16 "buttons".
However, the work may already have been done for you. I noticed in one of the authors photos on his page about ArdSimX, that there is a picture of an Arduino board. The link on that page to the ArdSimX interface didn't work for me. However, if you go to SimVim.com, there is a load of information there. It also indicates that the Arduino board they use is a Mega2560.
That Mega2560 is what I was trying to figure out. After you mentioned that model number I knew you must have found that info somewhere. It then dawned on me that I needed to go look on the page for the instrument panel to see what he was using.
Thanks for the wake up call....
I purchased the components for my transponder project. Everything has arrived except the rotary encoder. That should be arriving mid October.
So here is a picture of all the components with some 3D printed test fit faceplates. The final faceplates will ultimately be cut out of acrylic and engraved.
So how do I turn these components into that transponder in the link above?
Where do I start?
I cannot upload the pic of those components even though it is a .jpg. Very frustrating.
One more try at uploading. This time I will try a .gif.
So how do I turn these into that transponder?
I would start with sending some fixed transponder data to the sim. I think you are using xplane, is that right? Whichever it is, just prove to yourself that you can communicate with it.
It's been a long time since I used x-plane and a Silicon Graphics machine to do some simple aircraft dynamics simulation of real military avionics. I wish we'd had SimVim back then!
I had a quick look around the SimVim website. It seems that you need to program the Mega2560 with the SimVim software. You then need to run the configurator to tell SimVim which pin you have used on the Mega2560 for each discrete button.
They have a layout of a KT76C that you click on and assign discrete pins to each button. I had a quick play and it looks like the rotary switch is expected to be encoded into 3-bit binary so you may need to use a bunch of diodes to create it from your discrete switch positions. Unless, of course, your rotary switch encoded the data itself.
If you are not familiar with SimVim, then maybe start with something very simple just so you get the hang of configuring signals. Discrete inputs such as weight on wheels, undercarriage uplock etc were always favourites for us as they were dead simple for us to check.
Once you figure discrete inputs, try discrete outputs and drive an LED. You should then be able to figure out using serial signals to control the MAX7219.
If all else fails, have a look around the SimVim website, FAQs and forum.
Baby steps...
I am using X plane and installed the Simvim plugin per the simvim instructions. Then also per the simvim website I uploaded the firmware to the Mega and as they suggest hooked up pin 5 and ground to one of the button switches. That button then actuated the pitot heat switch in x plane as it should. So I know the mega is connecting and working. Now comes one of the hard parts...how to connect the 8 digit 7 segment display.
On a transponder like that when you select one of the numbers it automatically goes to the first character and displays that number, immediately after that the signal will jump to the second character awaiting the next number button push..and so on until all four have been selected. What I don’t really understand is how that is accomplished with the one momentary switch. Can’t find anything online about the concept of that.
I don't know the specifics of this particular control unit. Generally operation is simple to avoid the pilot spending too much time looking down at instruments rather than out the cockpit window.
There are 8 digits and 8 buttons. I'm going to guess that repeated presses of button 0 increment the left most digit. Pressing button 1 does the same for the next digit and so on.
As to the actual way it's done in software on x-plane it could be done on the Mega or within the actual x-plane software. I'm guessing that it's done in x-plane and that the Mega just collects button presses and sends them back to x-plane. X-plane then tells the Mega what to display on the display.
I have been trying to track down the guy that built the unit in the original post. He could certainly explain how this is wired and programmed but I have had no luck in contacting him. The video in the link below shows how the transponder works in the flight sim aircraft. When any of the numbered buttons are depressed the first digit of the code is placed in the first of the four readouts and dashes out the other digits. There is also the clear button and the button to automatically set all numbers to the VFR code of 1200.
I frankly don’t know yet how much of that is handled by Simvim programming or by X plane datarefs and commands. This is a complicated project. First thing though I need to figure out how to actually hook up buttons to the Max7219.
This Youtube video called "Using & configuring TM1637 and Max7219 7-Segment displays with SimVim Cockpit" may help you out with the MAX7219.
The MAX7219 is a display driver only. It doesn't connect to buttons. It took a bit of searching through the SimVim website but I did find this web page that talks about the MAX7219.
After watching a video on the operation of the KT76C, I can see now how the buttons 0-9 work.
It's been a long time so I can't remember if X-Plane lets you change radio settings using mouse button clicks on the virtual instruments on the main screen(s). If it does, then you may be able to start small and just connect up the MAX7219 to your Mega2560 to simulate just the 7-segment display part of the KT76C and use the mouse to actually change the settings.
You can them move on to adding the buttons. These seem to be wired directly to the Mega2560 pins (not the MAX7219).
When I clicked on the Configurator (on the SimVim website) and selected the KT76C XPDR, I could select the '0' button and then select a pin on the Mega2560. I chose Pin 2. The configurator then filled in pins 2 to 9 for this function. That indicateed to me that each pushbutton should be wired to pins 2 thru 9 on the Mega2560.
Thanks for tracking down that YouTube video. But being a total newbie at this the terminology is throwing me. Things in that video about “power distribution block”, “common rail”, “multiplexer”, and “data bus“ As it relates to the Mega 2560 throw me off. I understand what a power distribution block and a common rail / bus is as it relates to my boat stereo power system. I know what the concept of a data bus is, I think. I have no idea what a multiplexer is. The use of resistors are also new to me. Dont know if they are needed or not. I have a lot to learn yet.
As far as X plane is concerned the mouse is used to push buttons and turn knobs on the aircraft panel displayed on the monitor screen.
A data bus is generally an electrical link between 2 or more devices used to exchange information, either in one direction or both directions.
From Wikipedia: In electronics, a multiplexer (or mux; spelled sometimes as multiplexor), also known as a data selector, is a device that selects between several analog or digital input signals and forwards it to a single output line.
Your first step may be to start small and wire up just the CLR button to your Mega2560. With a bit of luck you can then use your mouse to alter transponder settings on your virtual instrument display. Then try the CLR button to see if it works.
Then I would wire up the pushbuttons 0-7 to the pins on your Mega2560 and see if you can get the transponder display to change on your virtual cockpit display.
If that works, then I'd go ahead and wire up the rest of the individual buttons. Then move on to the rotary switch.
If all that goes well, then I'd progress to the 7-seg display (or you could try that first).
Failing all that, you could always register on the SimVim website and ask questions there as it's highly likely that others have built their own control units. I wouldn't go looking specifically for a KT76C (but you could), as any control unit that uses buttons and 7-segment displays is likely to provide you with lots of hints on how to wire it all up.
Still scoping out web sites. This was one of them.
Have a look at this, seems like a good tutorial.
