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CAD and the Jeston Nano

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Robo Pi
(@robo-pi)
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Posted by: @robo-pi

What's a mil?   0.001 inch?  What does 6/6 mils mean?

I found some answers.

Yes, a mil is 0.001"

and 6/6 mils on the PCBway site means a min track width of 6 mils and min track spacing of 6 mils.

So I've got that cleared up.  Now I'm watching videos on YouTube to learn how to set track widths in KiCAD v5.1 ? 

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James


   
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codecage
(@codecage)
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@robo-pi

I think you hit the nail on the head with defining a mil!  And the trace size can be changed with a drop down menu just like the grid size.  Not looking at it right now, but think it is on the very left just below the ribbon bar.  And there is a place to set your trace sizes based on the type of signal.  Right off the bat I don't remember where you do that.  I'll have to open it up tomorrow and start a new design or look through my PDF copy of the book.

And I'll say again that the book is worth way more than the cost!

SteveG


   
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codecage
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@robo-pi

I believe DigiKey has some videos but when I started watching they were made with Ver4 and the software was already Ver5.  I think they have done some updating to their videos but I haven't gone back to them after using Peter's book.

SteveG


   
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egers
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@codecage

Posted by: @codecage

And I'll say again that the book is worth way more than the cost!

I found This book https://smile.amazon.com/Make-Your-Own-PCBs-EAGLE/dp/1260019195/ref=sr_1_fkmr3_1?keywords=pcb+with+eagle+designing+book&qid=1576209328&s=electronics&sr=8-1-fkmr3 at my library, but it uses Eagle. Again, I want to see what making PCBs is all about before I invest. Does anyone know anything about eagle?

@robo-pi

I have the same problem with changing micro sd cards on my rpi. If the project goes through, you already have one potential buyer ?


   
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Robo Pi
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Posted by: @egers

I have the same problem with changing micro sd cards on my rpi. If the project goes through, you already have one potential buyer ?

If it works I'll let you know.   I haven't built the prototype yet.    

I never really needed this with the rpi because I didn't have a need to change OS cards real often.   But I'm using this Jetson Nano like a  desktop computer and I'd like to change the OS card on the fly quite often.  I'm back and forth between A.I., CAD, and Video Processing several times a day.  All of which I'm doing on the Nano, and I don't want them all on the same system SD card for various reasons.  I also might be adding ROS to the mix as well.  That would be yet another SD card.  So being able to switch system SD cards with the flick of a switch will be quite nice.  Of course, you still need to shutdown and reboot.  But at least you don't need to be going through all the trouble of swapping out the SD cards.  That gets old real quick when you're doing it 3 or 4 times a day.  Just select the system you want to boot up, and off you go. ? 

 

 

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James


   
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Robo Pi
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Posted by: @codecage

And there is a place to set your trace sizes based on the type of signal.  Right off the bat I don't remember where you do that.

I found all the settings.  In V 5.1 it's actually a button on the toolbar called "Board Setup".  Alternatively you can launch it from the File menu/Board Setup

I played around with the settings and then ended up  going back to  default settings anyway.  But now I know how to do it.    I also like the idea that you can assign specific trace sizes to specific nets.  That's cool and I can see where that can come in real handle on various projects.

In the meantime I've been laying down traces and it's going really well.   It basically forces you to obey the rules settings that you made in the Board Setup.   It's extremely easy to run traces and apparently the grid size you have chosen has little to do with it except when you actually connect up to a pad.  You need to  have  grid settings that are compatible with the center point of the pads you are working with.  I probably could have set things up a bit better from the get go.   But it's working pretty well as-is.

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James


   
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Robo Pi
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All Done! ?

Well, I still need to test the circuit to be sure it actually works.   But other than this the PCB is finished and ready to be ordered.   Of course I'll probably refine it several times before I actually order.  That's going to be about two months from now.   Give the parts a month to come in.   And then give me a month to build some breadboard prototypes and fix all the problems. ? 

So I might be looking at ordering PCBs near the end of February.   Long time off.   If anyone has any suggestions or refinements to offer please feel free to speak up.  Also if anyone wants the KiCAD files let me know and I'll post them somewhere.   Maybe I could post them on my GitHub site.

In any case, here's the finished KiCAD drawings.

Front layer tracks:

FrontLayer

Back layer tracks:

BackLayer

Front 3D view:

FrontView 3d

Back 3D view:

BackView 3D

I hope I have the correct footprint for the 74HC4066 chips.  They look kind of big to me.  We'll see when they come in.

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James


   
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codecage
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@robo-pi

Did you try adding a copper fill on the back side?  And what about mounting holes?

SteveG


   
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Robo Pi
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I left enough room for the mounting holes but haven't drawn them in yet.

I did want to ask you about the grounds because I'm not real happy with they way they currently are.

Well, for one thing I'd like to make the ground  traces much larger.   I figured that I'd wait until I was done and then thicken them up.   One reason for that was that I had absolutely no clue where this was going when I first started out.   And yes, I would like to add large areas of ground copper, but I really don't have a clue what I'm doing so I'd just basically be making things look "pretty". ? 

In any case, I do have a concern with a possible ground loop that I created and should probably remove.

Here's a picture of the back of the board with the ground traces highlighted in red.

BackLayer GND

I basically have two ground lines coming from the SD cable connector.  One goes along the bottom and basically goes to all the ground pins of the 74CH4066 chips.   The other trace goes up to the ground of the LEDs and also serves as the ground for the SD Cards.   I drew in arrows to show where that little ground trace between the vias actually ties into the upper ground trace.  

On the far  right of the board you can see the trace I drew in  yellow.  This actually creates a  ground "loop".   Tying the upper and lower ground traces together at the far end.   I'm thinking I should  probably remove that loop  as it's basically redundant and may even cause problems?  So I'll probably just remove the trace I highlighted in yellow as it's not  really needed.

But I would like to go over all these ground  traces and make them quite a bit larger and possible even add areas of copper just because it seems like a good idea. ? 

Keep in mind that only one SD card will ever be activated at any given time.   So there's no worry about cross talk between SD cards.

Another thing  with this design is that I just blindly (lazily) decided to switch all 8 of the SD cable connections to every card.   This is really overkill and I'm sure with some thought this could be made a bit simpler.  For example all the SD cards could just remain grounded permanently.  I actually have the grounds switched too.  Only because the switches were available.   I probably wouldn't even need to switch the  3.3 volts off either.   But I just switched the entire cable from card to card just to be a simpleton I guess.

Here's the ground traces on the front of the board.  I highlighted these in light blue.

FrontLayer GND

The light blue traces at the top shows what I was pointing out with the red arrows on the back.  The top gnd circuit is solely for the SD cards and the indicator LEDs.    The bottom gnd circuit (entirely on the back of the board) is for the 74HC4066 chips.   So I  probably shouldn't be tying those two together at the far end as I've shown with the yellow trace on the back.  I think I'll just remove that yellow trace altogether.

But yeah Steve, I have no clue what I'm doing when it comes to good PCB practices.   But I was planning on fattening up the ground traces if nothing else.   Adding ground  planes is  probably a good idea.

Note that on the front of the board the SD card sockets are basically ground shields too.  They will also be connected to upper gnd circuit.

So the upper gnd circuit has the   LED grounds, the SD card socket shield gnd, and the actual ground for the SD card itself, and the latter ground is turned on and off by one of the  74HC4066 switches.   As is the 3.3v.

I don't know if this will even work.  But it's a fun little project to learn KiCAD with, and if it works out I'll be really happy to  have a  4-card  SD Boot Hub.  This will be so cool if it actually works!  ? 

~~~~~~~

By the way, just getting back to KiCAD itself.   I made a lot of mistakes setting things up initially.   I was using different grid patterns when I placed the  IC footprints than I was using when I ran the traces.    So things weren't lining  up perfectly.  But hey I learned something!  Take your time when setting things up initially and  things will go much more smoothly later on.  Live and learn.

In fact, I might redo the whole shebang from scratch just for the learning experience and to see how nice it really is to work with when things line up perfectly. ? 

I'm sure there are a lot of improvements that could be done at the schematic end as well.   But this is good enough for now.  Maybe I'll play with it again later.

 If you have suggestions for ground planes let me know where to put them.  If you want a copy of these files  let me know and I'll post them on my GitHub page.   But beware that the components weren't placed perfectly to begin with so that kind of threw everything off a bit.

DroneBot Workshop Robotics Engineer
James


   
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codecage
(@codecage)
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@robo-pi

Don't know if this will help at all, but have attached a pic of my power distribution board as seen from the top and I have removed everything from the view except the ground trace on the reverse side of the board.  The second pic is from the back of the board with the copper fill shown.  Since I had only ground traces on the reverse side of my board you don't see any traces as they have just become part of the copper fill.  Your board would have traces for all signals not part of the ground net.  I have edited the photo with circles to indicate which holes are part of the ground copper fill.  And notice on the pic from the top, the "green designed" line running around the board just inside the board outline.  This indicates where copper fill is located and is shown or hidden with the following "buttons" on the left menu bar of the PCB Layout editor.

ShowHideFilled

View from top of board:

PDB TopwGND

 

View from bottom of board:

PDB Bottom Inked

 

SteveG


   
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frogandtoad
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Posted by: @robo-pi

Yes, a mil is 0.001"

If "mil" represents "Millimeters", then your assumption is incorrect - There are 25.4mm in 1 inch, therefore:
1mm == (1"/25.4), which is equal to: 0.0393700787401575"... but lets round it down to: 0.0394", preferably: ~0.040 🙂
So, 1mm is effectively equal to: ~0.40"


   
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Robo Pi
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Posted by: @frogandtoad

If "mil" represents "Millimeters", then your assumption is incorrect

It wasn't an assumption.  I looked it up.  There's even a conversion available on Google.

Just type into  Google something like "6 mils to mm" and it will tell you the 6 thousandths of an inch = 0.1524 mm.

I think they use mils  (or thousandths of an inch) because in the electron component industry many ICs and other components are based on 0.1" pin spacing.   So they are kind of stuck with using inches even when working in mm.    Although you could  just say that 1 mil =  approximately 0.0254 mm.  But that's just an approximation.

In fact, I guess this is why in KiCAD they offer all these seemingly weird grid sizes.   They aren't really weird at all, they are just the closest millimeter approximation to inches.

The imperial and metric systems were bound to clash head-on and in the electronics industry it appears to be a full-scale collision because so many components were designed using the imperial system and it has become an industry standard.   All breadboard are based on 0.1" hole spacing.

  I actually have a machine shop and I know they often use the term mils to mean 0.001" inches.  I just didn't realize this is also used in electronics.

So yeah, mils = 0.001".

 

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James


   
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Robo Pi
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Back to Blender again.   Actually I'm not doing anything in Blender today.  I'm just now downloading version 2.81a on the Jetson Nano.  I don't know if this will run on the nano.  I made a whole new SD system card just to give this a shot.  I still  have version 2.79 installed on another SD card in case this doesn't work out.

There seems to be some seriously major upgrades from  v2.79.   So since I'm just now starting to learn Blender I figure I may as well  get onboard with the latest version.   It's about half-way downloaded already so  I might be finding out pretty soon whether or not it will run on the Nano.

In the meantime I think I'll start setting up a place for my second nano.   I haven't tried it on a VGA monitor, so that's the first thing to try.  If that works I'll go with that for now.  Otherwise it's off to the store to  go even further broke buying another HDMI monitor. ? 

Maybe I should wait until after Christmas.  I might get a better deal buying a left-over or a return. ? 

DroneBot Workshop Robotics Engineer
James


   
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Robo Pi
(@robo-pi)
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It's a NO GO! ? 

I got the message: Blender is not available for this architecture (arm64), but is available for (amd64).

So apparently it won't run on the Jetson Nano.

That's strange.  I wonder why version 2.79 runs on arm64?

Oh well, I tried.

I guess I'll just go back to v2.79 and play with that version.   That will probably do everything I want to do anyway.

DroneBot Workshop Robotics Engineer
James


   
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frogandtoad
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Posted by: @frogandtoad
Posted by: @frogandtoad

If "mil" represents "Millimeters", then your assumption is incorrect

It wasn't an assumption.  I looked it up.  There's even a conversion available on Google.

Actually, I believe I was right, and I'll explain why.

I did some research, and I found from the following link and others, that the "mil" as you speak of here, does not refer to the "Millimetre" at all.

I found that your calculation presented was correct from what you have read in some pages, but it does not refer to the "Millimetre" at all, rather the real name of this so called "mil", appears to be the "milliradian", according to Wikipedia here: The Milliradian

The problem here is that the meaning of the word mil was, and as far as I'm concerned, is still a well recognised shorthand alias, associated with the unit called Millimetres, especially in the engineering game, let alone any others.

By the way... I am a qualified Toolmaker and have never given up study, as I believe in life long learning.

Prior to the last 15 years in IT, I was in the engineering game for nearly 30 years, and whenever an instruction was put forward to take a couple of mil of the face of a block of steel for example, they were referring to "Millimetres", and expecting the person to only remove 2 (Millimetres), NOT 0.002" (two thousandths of an inch).  No one in their right mind would have only removed 0.002" under such an instruction, period! 🙂

I haven't installed KiCAD at this stage, but using the term: "mil" (which is a well known alias for the Metric Millimetre), is not a good thing at all IMHO!

Cheers!


   
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