Building a NAV/COM radio

[shy wedge]

Digikey is very expensive so I only buy from them when I can’t find another option.

[autumn thorn]

It appears solder has gotten significantly more expensive since last I bought a spool 😄

[shy wedge]

Don’t quote me on this but I think Tariffs have something to do with some of this lately.

[autumn thorn]

@kind tulip how does SnAgCu compare to SnAg in your experience?

I'm sorry, @river river I'm hijacking your thread again

[kind tulip]

I am not really that experienced

[river river]

The hijacking is an educational detour for this novice.

[shy wedge]

Yea I apologize also.

[river river]

These tangents apply to what I am doing since I have begun the soldering on my radio PCB. Fortunately in the states I am still allowed to inhale PB solder fumes.

[lofty valley]

Now I wonder if 4 rolls oi got Ali are lead free or is it just garbage.
I couldn't solder anything with temps going up to~380 degrees

[autumn thorn]

That sure sounds like lead-free

[quartz walrus]

Honestly have not had much issue with lead-free at like 350 other than ground pads taking forever to heat up

[kind tulip]

yeah over 400

it melts at 350 or so but does not flow

it just makes a crumbly mess

once you heat it enough it works

sticks to iron tip but not on the component or PCB

[quartz walrus]

Pretty sure mine melts in the mid-to-high 200s. Need to check temperature

and it definitely wicks up stranded wires as well

[autumn thorn]

Sounds problematic for any sort of hot air reflow work... I'd feel uncomfortable heating ICs to 400°C

[hybrid sedge]

that is exactly my same concern. smd leds for example I'm pretty sure they would melt almost instantly at 400+ degrees. As long as I can have proper ventilation that send fumes far from my nose and mouth, I'll stick to SnPb

[quartz walrus]

fumes are mostly flux. It has been said that lead-free fumes are worse for you than leaded

[autumn thorn]

I tend to solder SMD LEDs last using SnBi solder for its low melting point. I've had plenty of LEDs discolor or melt in the past but they don't seem to mind 180°C.

[hybrid sedge]

Never thought of
SnBi... that's the same compound you find in solder paste sold in syringes, right?

[autumn thorn]

Yes... so-called low-melt solder...

[quartz walrus]

Why am I now thinking Field's Metal

an InBiSn alloy that melts at like 62 °C

[hybrid sedge]

I don't want to further hijack this thread so I'll just post a link to my finished RMP module in showcase: https://discord.com/channels/608690978081210392/1435748072331280434
I'd really like some opinions, advice and comments on this work. It has been fun as hell to do

[river river]

Is the black enclosure all 3d printed? I am considering enclosing my radios and would like to have usb and power connectors that are panel mounted also. What did you use for those connectors?

[hybrid sedge]

Yes, everything is 3d printed. The back enclosure consists of two pieces, one supporting the arduino pcb and the other is the cover. I split in two parts to be able to mount the arduino and pass all cables without becoming crazy.
Barrel jack and USB connector are soldered on the arduino board

[river river]

Looks very professional. The back of my enclosure will be a few inches from the pcb mounted arduino and the power screw terminal. So I think I will need a panel mount to arduino usb extension if there is such a thing. And a way to extend the power cords from a barrel jack to the PCB power terminal.

Maybe another small PCB that the connectors are mounted on ?

[hybrid sedge]

If what you need is just a way to bring the signal to the board you could do something like what I did in the picture. It's effective and you could do the same for the barrel jack too

[quartz walrus]

There's commercial solutions for that with mounting flanges and everything, too.

[hybrid sedge]

Yeah, but I had a bunch of spare connectors 😄

[quartz walrus]

Fair game. Just listing options.

[river river]

I should be able to find a way. Sometimes there are too many options.

[kind tulip]

bismuth?

[olive storm]

I choose to believe this 🙂

[autumn thorn]

Yes
Tin-Bismuth solder works really well for SMD LEDs in my experience with its 138°C meltingpoint and ~165°C minimum soldering temperature. I've only ever used it in conjunction with a hotplate so I cannot say whether it works well with just an iron. It is said to crack if the joint cools down too quickly, but I can't confirm this.

I have found that generous quantities of flux make clean-up easier, as SnBi tends to create a lot of solder balls.

Over all, my workflow when populating PCBs has been:

• Wet all pads on the bottom side with SnPb solder (soldering iron and flux)
• Place all passives on the bottom side of the board and heat them enough to melt the flux, tacking them in place (usually just using the hotplate at around 100°C)
• place all ICs on the bottom side
• reflow bottom side (hotplate set to 150°C starting from cold, additional hot air at 240°C once the board is warm)
• on the top side, wet all pads with SnBi solder and apply flux
• place LEDs and any passives (usually just LED current limiting resistor)
• heat the board on the hotplate to around 100°C, then hot air around 180°C to reflow the LEDs and passives.
• let the board cool on the hotplate

Generous Isopropyl bath and toothbrush to clean up the solder.

Speaking of which: what are your guys' thoughts on ultrasonic cleaners for PCBs? Christmas coming up and I haven't gotten myself anything yet 😅

[kind tulip]

I have one but for my resin prints

[autumn thorn]

I forgot the final final step: hand solder the SMD electrolytic caps 😅

[autumn thorn]

What do you use to clean PCBs? Just isopropyl alcohol as well?

[kind tulip]

yeah, or if I solder without flux, nothing really

depends on the case

I know flux is the way to go for good joints of course

but I mostly get SMD done by jlc and solder USB port and encoders etc as tht , then maybe toothbrush and isopropyl alcohol

[quartz walrus]

I got an ESD brush with an air duster I bought

[kind tulip]

or just paper towel if it is not a hard to reach mess of pins

or qtip might work also

[autumn thorn]

Just googled what you mean by air duster, @quartz walrus
Do you use yours to remove 10cm of snow off your car, too?😅😅😅

I never considered a dedicated ESD brush... now I'm obsessing over whether I need one😅

[quartz walrus]

Have not tried it yet, but now I am curious to test it

[hybrid sedge]

Like these? 😁

[kind tulip]

or a spray air can, but I guess that is smarter on the long run if it doesn break too quickly

[hybrid sedge]

the mini vacuum is pretty weak, but the dust blower is a very nice tool. Powerful too, comes with lots of accessories. Bought on aliexpress a couple years ago

[river river]

I am almost done with my NAV/COMM radio and already planning for two additional radios...a DME and and ADF to match what is in this JF PA28 arrow that I fly in Xplane.
I purchased a DME PCB from the captainbobsim website and can use it with the 3D printed faceplate .stl files that I downloaded.
But I also have the actual DME faceplate. Unfortunately, the PCB is not quite the same size as the actual DME faceplate. I am still mulling over what to do with that,
I also have the actual ADF faceplate (actually the entire radio) which will probably be a matter of changing the mechanical display to a 4 digit display.
The DME has (3) 3-digit display where only 8 digits are used and thus a single Max7219.
The ADF radio would need a 4 digit display that of course can easily be handled by a single max 7219.
What I have going through my mind is how to connect both of these to a single mega 2560 pro.

The DME requires 16 pins so I think there will be plenty for both radios.
The top radio in this panel is just about completed. The two below it is what I would like to build and combine into one MCU.

[river river]

I see the airliner panels and always wonder how the PCBS MCUs and connections are all handle for multiple components.

[hybrid sedge]

MAx7219 can be daisychained up to four (32 digits) if my memory serves me well. In any case, you can absolutely daisy chain 2 of them (i did the same for the RMP)

You will need to connect only one 7219 to the mega, and use the out->in pins in the chips

[river river]

One 7219 can drive 12 digits?

[hybrid sedge]

up to 8 digits

so you will need two for 12 digits

[river river]

That is what I thought.

[hybrid sedge]

Well, i was even conservative, you can daisychain up to 8 max7219 in Mobiflight

up to 64 digits total

They will share the CLK and the load (CS), and you will jump from DOUT of one to DIN of the other

[river river]

Thats what I did with the (4) 5-digit displays on the NaV/COMM radio.

I am just trying to get a picture in my mind on how all of this stuff ,PCBs, MCU, power cables might be organized between two radios.

[kind tulip]

@river river so does the pcb work?

did you already try it out?

[river river]

I will finish it up this weekend.

[river river]

As Dr. Frankenstein once exclaimed...."It's Alive !"
But there is one little problem. One digit is not working.
Does anyone have a suggestion on where to start the troubleshooting?

The parts that are working are communicating with Xplane very nicely.

[quartz walrus]

I'd check the digit pin on the driver chip and the LED module first

[river river]

Multimeter continuity?

[quartz walrus]

sounds fine

[river river]

Ok..thats a start. Thanks

[hushed wind]

Check the wire for that number dig5 (assuming right to left starting at 0)

[river river]

Roger that

[hybrid sedge]

nice job!

[river river]

Thanks. I am glad it mostly works.

[kind tulip]

that looks super nice so far!

and yes, it is likely the cathode (digit pin) that is cut if its all blank

[quartz walrus]

flashbacks of the 2025 meetup... Spent quite some time helping fix broken 7-segment displays...

[autumn thorn]

@river river Do I remember correctly that you have your 7seg modules mounted in dip-sockets?

If so, try bending all pins on the 7-seg modules ever so slightly, all in the same direction to make assembly possible. This should improve contact between the pins and the sockets.

[kind tulip]

also try swapping two digit modules around and see if the issue moves

but yeah, some segment modules have quite thin pins and the sockets might not make firm contact, just like @autumn thorn said, bending them will make a bit more "springy" contact

[river river]

Yes I am using the dip sockets for the chips. For the modules I am using the round machine pins. Swapping the modules and checking the chips will be the first things I will try today.

[river river]

Swapping the display module was the fix.

[kind tulip]

likely a bad connection in the pin

but yay! a working radio! How cool is that??

@river river you could make this a #showcase post with some in progress photos and short story?

[river river]

It's a milestone for a first time PCB designer.
Setting up a #showcase might be okay but compared to the projects others have done, this radio is quite unremarkable.

[kind tulip]

no it is absolutely not unremarkable

dont be too modest, it looks really cool

[quartz walrus]

Getting to the PCB design stage puts you ahead of the vast majority of flight simmers already. And finishing it with a beautiful and functional device is definitely something to be proud of and something worthy of showcasing

[river river]

Perhaps I can grab a few past photos and compile something.

[autumn thorn]

What @quartz walrus said!
Not a chance I could say it better!

[river river]

Now that I have learned a few things, I want to create a second version.
I am not satisfied with the pots and the screw terminal power connector.
A barrel connector might be better for the power.
The barrel power connectors come in different diameters for the male and female connectors.
I have some male and female connectors with pigtails, but if I order a board mounted barrel jack, how do I make sure its the right size for the male connectors I have?

I think I know now.
The male plugs I have are 2.1 mm. I just need to get a matching 2.1 mm PCB mounted right angle jack.

[hybrid sedge]

and then you will create a third. And you know what? Every time will be better than the previous one. And you'll learn something new every time. As others have said, post in showcase because this is by no means a poor job. This is actually very cool to look at. Be proud of it!

[river river]

Thanks for the words of encouragement. I am looking forward to spending more money on another better version.

[river river]

The challenge was always in dimensioning the encoder and potentiometer holes in the faceplate and figuring out where to place the components on the PCB so that the shafts align precisely with the center of the faceplate openings.
My first try was to get them close as I could and rely on the knobs to cover the holes and the misalignment.
Now my OCD is kicking in and I want to get the alignment dead on so the knobs that will be custom 3d printed will fit inside the holes as they do on the actual radio in the photos.
That will take some trial and error and a number of 3d printed test fits to get the shafts on the PCB to be dead center on the faceplate holes, or at least within a half millimeter or better.
Then the revised PCB design will be shipped off for round two.
Buying a unit with the actual knobs as shown is a costly endeavor so using the new P2S printer will be a more cost effective way.

[supple wigeon]

i recommend to export your pcb as step file and import it in FreeCad / Fusion and model "around it"

or do the iterations then with going back and forth between CAD and KiCad

[hybrid sedge]

exactly that. Freecad makes this a trivial operation and you will never have to worry about alignment again

[river river]

Dimensioning the faceplate can lead to errors.
So I have exported the PCB as a step file and imported it into Revit. Then adding cylinder extrusions that match the diameter and location of the openings in the faceplate. That will be 3d printed and then placed on the back side of the faceplate just as my PCB is mounted. Currently the holes are within +/- a millimeter but they need some fine tuning.
Once I get the holes correctly located on the Kicad PCB, The datasheets for the pots and encoders should then help to determine the exact center of the shafts relative to the PCB pins.
What has been a challenge so far is drawing the required matching geometry in Kicad. It doesnt have the easiet drawing tool. The grid snapping makes it difficult to accurately place circles and lines.
But once I get the Revit cad file correct I can export that into Kicad to locate the openings, then try to orient the component's body and pins relative to the openings.

[supple wigeon]

i got 3d models for my encoders in kicad linked with the footprint. So when i export to step file it will include these 3d models - nothing to guess in CAD

[supple wigeon]

you can also disable grid snapping in kicad and just place anything anywhere.

[kind tulip]

there is also the kicad stepup workbench in freecad that lets you move the encoders in Freecad to nudge them and it can move them in the kicad file 🙂

but it is a bit complex workflow

I also often 3d print the pcb before ordering

it sounds silly but helps test fitting a lot

[supple wigeon]

i also print the PCB first to verify fit

[kind tulip]

printing it with the 3d models of components included, I just flatten the bottom side through hole pins

so it prints flat

[quartz walrus]

I have done some crazy prints before...

copied a PCB layout, but printed out some recesses for the buttons since the tact switches I had on hand were taller than the ones I was ordering

[supple wigeon]

or mount the actual components

the pcb will be floppy but it is still good enough to check for an obstruction or misalignment

[quartz walrus]

so I could put real tact switches under the button caps and see if the button cap thing works

[river river]

Without a 3D printer, sim building would be much more difficult.

[kind tulip]

yeah

sheesh, 20 years ago

this was schaeffer-ag.de

[quartz walrus]

interesting knobs

[kind tulip]

yeah, only ones with a hole through

the small knob is missing

[olive storm]

@river river what @kind tulip said this looks fantastic

[river river]

The second iteration will have some adjustments.

[kind tulip]

this is a rabbit hole of rabbit holes 🙂

[river river]

Rabbit hole / money pit.

[hybrid sedge]

Just make sure you never try to calculate your expenses for these projects. Trust me. I could have a couple of winwing complete sets or even some professional one, with all the money I spent in pcbs and components 😅

[river river]

Roger that.

[kind tulip]

the money goes to something anyway

[river river]

As Don Henley sings...."you dont see no hearses with luggage racks."

[river river]

What's the best way to create a new Kicad 9 file from the original for versioning?
Through a google search two methods are given;

1. For entire project - Select Archive Project
2. Manual Copy (Simple Versioning) - Copy entire project folder or the key files and paste into the same folder then rename.

[kind tulip]

I think you can also save project as

kicad can also do git stuff it seems

[river river]

I read about the git options, but still that whole setup is very confusing to me.
Its got to be simple for this old brain

[river river]

I will try both options (no github).
My concern is making sure I do not lose connections to the libraries.

[kind tulip]

libraries are saved in kicad main settings I think

so they will be "global", you can of course also have a project-local library, depending how you did it

but if that gets added to version control too, it should then work

[river river]

Sounds good

[river river]

When I started this Kicad project I was still learning the file structure and now when looking at the project folders to create a copy I am seeing a lot of files that were accidently placed in the primary project folder.
It would be best to be clean up the files before making a copy it seems.
The primary project folder originally came from Github when I downloaded the first project files to get started.
Over time all of these files have found their way into the primary project folder due to my inexperience.
These are the files that have accumulated over the last 5 months.
It seems that many of these files can be deleted, especially any .zip files and those gerber files.
@kind tulip Can you verify what I have marked up can be deleted and what about those files with the question marks?
The .....missing 3D models.txt files are confusing.

[kind tulip]

I think you only need to copy the .kicad_* to a folder and it likely works

you can try that

if you open then the .kicad_pro

but try if you just copy those files to a new folder named the same as the project file but without the .kicad_pro in the folder name

[river river]

Thanks

[river river]

I know this is simple but I am having a brain block.
These pot wiring diagrams are confusing me.

The datasheet shows pins 1, 2 and 3 on the Bourns pot that I purchased. Pin 2 is the wiper.
Are pins 1 and 3 to be the GND and the 5V respectively? (or even 3.3V)

Pin 2 will go to one of the analog pins on the Arduino Nano I believe.
Pins 25 and 26 are available on the Nano which seem that either will work for that.

Do I have this correct?

[kind tulip]

@river river https://docs.mobiflight.com/boards/recommended/arduino-nano/

and https://docs.mobiflight.com/devices/potentiometer/wiring/

so "left" side connects to GND, and "right" side to 5V (or 3.3V on a pico)

and yes, the A6 and A7 are good for potentiometers on nano, because they do not work for switches or leds

[kind tulip]

yeah. test with prototyping board

but I have noticed that the dupont cables are waaaaay more unstable than soldered connections or traces on PCB

[river river]

I will be soldering the pots.

[kind tulip]

and the sensitivity setting in mobiflight pin config also helps a lot if it jitters a bit - I usually always have a bit of filtering set

but depends on what the potentiometer is for

like for light dimmer just crank it up and it will be solid, and you will not really suffer from the slight slowness and perhaps lower resolution, it will still work fine