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CAD and the Jeston Nano

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Robo Pi
(@robo-pi)
Robotics Engineer
Joined: 5 years ago
Posts: 1669
Topic starter  

I got everything dumped over to the PCB.  I have NO CLUE what I'm doing.  I just laid the parts out in a similar fashion to how I drew them up in the Schematic.   I have no idea how much room I actually need between components.   I have no idea how close to the edge of the PCB I should place the SD card sockets.  I'm guessing I should place them as close to the edge as reasonable.   No traces run yet.

The board is about 100mm by 100mm.   But for some reason it's not coming out exact.  I probably need to set some units up somewhere.  Here's the PCB layout:  I'm going to just have a header for rotary selector switch as I'll mount the switch on the case instead of on the PCB board.   I mounted the LEDs and their current limiting resistor next to each SD card slot.  This way the LED will be right next to the active SD card.

PCB

And here's the 3D view.

3D View

Now I need to learn how to run traces without shorting everything together. ? 

It would be nice if I had a clue what I'm doing.

Of course this can all be modified later.   The parts won't be here for a month.   And even after they come I'm going to try to rig something up on a breadboard to try the whole shebang out first.   Although I'm not sure how I'll get those SD card sockets to attach to a breadboard?  I only ordered 10 of them so I don't want to mess them up.

DroneBot Workshop Robotics Engineer
James


   
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Robo Pi
(@robo-pi)
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Posts: 1669
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Now that I think about this, those SMD chips look awfully huge!  I probably used the wrong footprint.   I'll need to go back and double check that.  Surely those chips aren't that big?   These footprints are as be as the SD card holders.  That can't be right.  I thought they were kind of humongous. 

I'll have to look into this.  I must have chosen the wrong footprint.

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James


   
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Robo Pi
(@robo-pi)
Robotics Engineer
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Topic starter  

Yep, wrong footprint!   Told you I was clueless! ? 

This is much better!

PCB
3d view

This is MUCH BETTER!  I might even be able to move these all up side-by -side  underneath the SD card sockets in a single horizontal row. 

I thought those suckers were HUMONGOUS! ?    I didn't know they made 14 pin SMD DIPS that huge, but evidently they do or KiCAD wouldn't offer such huge footprints. 

I think I got the right ones now, hopefully.   I'll double check when the actual chips come in.

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James


   
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Robo Pi
(@robo-pi)
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Topic starter  

Here's what happens when you're clueless,....

I looked at my order to see if I could get more info on the exact footprint dimensions.  But it just says 14 SOIC and that's it.  No specific info.

Then I looked up the SOIC footprint on Google and discovered it comes in 3 flavors: Narrow, Wide and Mini.

So now I'll continue to be clueless until the chips actually arrive.   Then I'll probably need to make my own custom footprint in KiCAD.

In any case based on the photo in ad where I bought them they do appear to potentially be Wide.   But I really can't tell because I don't know what Narrow and Mini look like.

In any case, I'll go with the footprint KiCAD gave me for now just to run traces.

 

 

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James


   
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Robo Pi
(@robo-pi)
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Ok, even though I'm talking to myself in this thread someone might be interested in this info in the future.

Apparently the chips I ordered are 14 SOIC Narrow.   Which is the last footprint I  posted on my PCB.   The first  footprint (the humongous one) I used wasn't even SOIC, it was something else.   That's was just a grave mistake on my part.

KiCAD does also offer a 14 SOIC Wide footprint.  But those chips are basically square rather than rectangular.   The chips I ordered are definitely rectangular.   So they must be the Narrow variety.

The SOIC Mini footprint isn't available for 14 pin ICs.   Only for 8 and 10 pin chips.    So these have to be the 14 SOIC Narrow.   So that's  what I'll go with.

So much to learn!  But at least I can be pretty confident that I'm using the correct footprint now.

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James


   
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Robo Pi
(@robo-pi)
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Topic starter  

Now we're getting somewhere!

The latest and greatest layout.   Still no traces run yet, but I have been looking at individual nets and this looks like it will be fairly easy to layout the traces.  I'll still need to learn how much room I'll actually need between these chips.   I'll discover this as I go.  Right now I'm going to bed.

Nice PCB
Nice 3D

This layout is far more like what I was expecting. ? 

Although even these chips look pretty big in comparison with the SD card holder.    If they actually are this big it will make the assembly and soldering a lot easier for me.

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James


   
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frogandtoad
(@frogandtoad)
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Posted by: @robo-pi

I have version 2.79.

I just wat

Yeah, that's quite old now, even 2.82 is in Alpha release and not far away, but be careful to check the specs, because I think as of 2.80, you required specific hardware specs for the graphics card for blender to work.

tutor4u is a great channel, and I've learn't a lot from his channel in the past!

Cheers!


   
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codecage
(@codecage)
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Posts: 1040
 

@robo-pi

Hi James,

Just so you're not just talking to yourself and there are some that see your posts, maybe not immediately, but eventually, I thought I'd jump into the conversation!

In KiCad it is best to define the size and shape of the board you're trying to design just after moving from the Schematic Layout Editor to the PCB Layout Editor and before you start moving components around.

And not to beat a dead horse, but this is something that is pointed out in the "KiCad Like a Pro 2nd Edition" book.  And just to be clear, I have no connection to the author or the publisher of this book.

SteveG


   
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Robo Pi
(@robo-pi)
Robotics Engineer
Joined: 5 years ago
Posts: 1669
Topic starter  
Posted by: @frogandtoad

Yeah, that's quite old now, even 2.82 is in Alpha release and not far away, but be careful to check the specs, because I think as of 2.80, you required specific hardware specs for the graphics card for blender to work.

That's one thing I'm afraid of.  This 2.79 version appears to be running flawlessly on the Jetson Nano, at least so far.    I'm afraid I might have problems if I try to upgrade to 2.8.   In fact, last night I made a copy of the Nano System SD Card.  This way I can try to upgrade to 2.8 on another SD card and it if turns out to be a disaster I can just plug  the original SD card back in and pick up where I left off with  Blender 2.79.

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James


   
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Robo Pi
(@robo-pi)
Robotics Engineer
Joined: 5 years ago
Posts: 1669
Topic starter  
Posted by: @codecage

In KiCad it is best to define the size and shape of the board you're trying to design just after moving from the Schematic Layout Editor to the PCB Layout Editor and before you start moving components around

That is the first thing I did just intuitively. I also wanted to choose a size that might be compatible with standard sizes offered by PCBway. It's still not clear to me exactly how PCBway charges, but it appears that a 100mm by 100mm board is potentially some sort of cut-off before a major price jump? I'm not sure about that.

In any case, it does appear that there is only a couple dollars difference between ordering 100mm x 50mm and ordering 100mm x 100mm. For this reason I'm thinking about mirroring the finished circuit on a 100mm x 100mm board when I'm done. This way I'll get twice as many PCBs for just a couple bucks more. I'll have to cut them in half myself. But still doubling the number of boards for just a couple bucks extra would be worth it.

So I'm thinking of mirroring the board I have shown in this post as it's only about 100mm x 40mm. So I can get two circuits on one 100mm x 100mm board.    

In any case, it will be a month before all the parts come in.  And I also plan on building a mock up on a breadboard first.   So it will be quite a while before I actually order these boards.  Hopefully I'll learn a few tips by then. ? 

Also, I can't seem to get the grid to work out perfectly for some reason.  For example I can seem to draw board edges that are prefect numbers.  Instead of 100mm I can only get something like 99.86 or 100. 67, or some other non-integer.  So I'm not clear on why the grid doesn't come out  perfectly.

I'm also not sure of the exact spacing of the footprint pads?   I'm going to need to study these geometries a bit more before I'm comfortable with them.  I want to make sure I have the grid set up so when I add traces they'll  snap to pad cleanly.  This may also have to do with placing the components onto the grid properly.  It's unclear to me exactly where the anchor points are on the footprints.  When you use the Move command to move a component where's the anchor point that will snap to the grid when you let go of it?  

These are tiny little things that I need to learn about.   As it is right now I'm feeling a bit confused about exactly how this grid is working, so I'd like to clear this up before laying down actual tracks.  I'd certainly feel better if I can get the board edge lines to fall on exact integers.  Not that it's important, but when they won't go to an exact integer this leaves me confused as to why this is?

DroneBot Workshop Robotics Engineer
James


   
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codecage
(@codecage)
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Posts: 1040
 

@robo-pi

You have done a great job!  I'd have to assume that you have discovered that you can change grid size at will and even create a custom grid size.  And have you discovered the "calipers" at the bottom of the right hand tool?  And also the ability to select multiple components to distribute, align, and move them how you desire?

Keep up the good work.

SteveG


   
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Robo Pi
(@robo-pi)
Robotics Engineer
Joined: 5 years ago
Posts: 1669
Topic starter  
Posted by: @codecage

And have you discovered the "calipers" at the bottom of the right hand tool? 

No I haven't tried them before.  I just now tried them and they are pretty cool.   ? 

However with with the calipers I can't place the mouse cursor exactly on the 100mm mark.  So I need to change something in the grid settings.

I have learned about using the SpaceBar to zero out the relative coordinates and that's nice too.  But that still doesn't change the grid spacing problem.

The other thing I don't understand is in the  lower right corner it says Grid: x 1.270000  y 1.270000   mm

I'm thinking this has something to do  with my problem.   Why isn't it reading x 1.000000  y 1.000000   mm

Or something like x 1.250000  y 1.250000   mm

What's the 1.270000  all about?  And how do I change that?

I confess that I just don't understand how to control the grid settings properly.   I would like to get this cleared up before doing anymore serious work.

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James


   
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Robo Pi
(@robo-pi)
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Posts: 1669
Topic starter  

Ok, I just figured out how to set the grid to x 1.000000  y 1.000000   mm and now I can draw a line that is exactly 100mm long.

But now the question is do I want the grid set to x 1.000000  y 1.000000   mm, or should I choose a different setting?   When do I change settings and why?

Also, are there any "standards" I need to know about?

Is any of this going to be important when ordering PCBs from PCBway?

The fact that they offer so many grid options on KiCAD suggests to me that there must be reasons why so many options are necessary.

So while I'm gaining some control over the grid options, I'm still confused as to which options I should choose and how they might affect the final outcome.

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James


   
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codecage
(@codecage)
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@robo-pi

Glad you found the grid change drop down.  I think it makes no difference whatsoever to the final Gerber files you send to PCBWay.  I have found that you can change grid dimensions as needed to arrange the layout of your design any way you want.

There are even two hot keys you can use to switch back and forth between your two most used grid dimensions.  I tend to use 0.1270 mm (5.00 mils) and 0.2540 mm (10 mils) the most.  I think it comes to personal preference as far as I can tell. 

SteveG


   
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Robo Pi
(@robo-pi)
Robotics Engineer
Joined: 5 years ago
Posts: 1669
Topic starter  
Posted by: @codecage

I tend to use 0.1270 mm (5.00 mils) and 0.2540 mm (10 mils) the most.  I think it comes to personal preference as far as I can tell. 

I'm just now beginning to realize that the grid settings will have a major effect on how far apart traces are.

I'm also not sure how to change the  trace width.  It appears to be set on a default of 0.25 mm trace width.

If I have the grid set on 0.25 then the closest I can lay tracks is 0.25 mm from each other.  If I set the grid to 0.20 mm, I can then lay the tracks a lot closer together.

I also noticed on the PCBway site that the min distance between tracks must be 6/6 mils (whatever that means).   Any closer and the  price of the boards skyrockets.    So I'll  definitely want to keep the tracks at least 6 mils apart I guess?

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

Like I say, I'm still trying to sort all of this out .

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James


   
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