Author Topic: First PCB for a beginner, where to start?  (Read 4095 times)

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Offline admiralk

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Re: First PCB for a beginner, where to start?
« Reply #25 on: July 30, 2021, 09:49:38 pm »
@tooki - Now I understand your confusion. I think two thoughts were running trough my head when I typed that. It should have been simply,
Quote
It might seem a pain at first, but after making a couple you will stop looking past the datasheet.
And as fourfathom pointed out, the alternative is to search for prebuilt patterns.

 

Offline JLynchTopic starter

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Re: First PCB for a beginner, where to start?
« Reply #26 on: July 31, 2021, 12:32:14 am »
About ready to place my order and I was able to locate all but three components for my board and taking some of the advice from above I created my own footprint for one of the parts.

One of the three I couldn’t locate is a through-hole part while the other two are surface mount. One of the two surface mount parts has large pads and shouldn’t be a problem soldering, same goes for the through-hole part. Only the one surface mount with very tiny pads is going to be a challenge.

Question, in laying out traces I started with the Auto Route function and then cleaned up / adjusted everything by hand. I’m using a USB Type-B connector for power which has 4 circuit related pins and two larger ones for securing it to the board. The Auto Route function created an isolated trace (connected to nothing else) between these two ‘fastening’ pins and the software gets mad when it’s removed.

I assumed that the metal ‘shell’ of the USB connector should be grounded but when doing so it seems to conflict or interfere with this isolated trace created by Auto Route resulting in a DRC error.

So not sure why Auto Route created this trace and why it’s causing a DRC error when replaced with a ground connection. So now I’m questioning whether or not to ground the ‘fastening’ pins of the USB connector of just leave the original Auto Route trace alone.
« Last Edit: July 31, 2021, 12:34:29 am by JLynch »
 

Offline fourfathom

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Re: First PCB for a beginner, where to start?
« Reply #27 on: July 31, 2021, 03:57:06 am »
I have the shell of my USB-C connector tied to the groundplane, and the schematic symbol includes these shell pins.  Most of the groundplane around the connector and transient suppression diodes has isolation "no-fill" groundplane cutouts, to keep transient spike current local to the connector and not spreading out into the rest of the board.
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Offline jpanhalt

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Re: First PCB for a beginner, where to start?
« Reply #28 on: July 31, 2021, 10:54:46 am »
I’m using a USB Type-B connector for power which has 4 circuit related pins and two larger ones for securing it to the board. The Auto Route function created an isolated trace (connected to nothing else) between these two ‘fastening’ pins and the software gets mad when it’s removed.


I use Eagle, but assume the same will apply to your situation.  As previously stated by fourfathom, there may be an assumption they are connected to ground.  That should be evident in the component drawing.

If you want them independent of ground and each other, one way is to rename them in the component so they are not connected (assuming you are using something equivalent to the Eagle "pad") to solder to.  A more complicated way would be a plated slot (assuming that is the correct geometry).  In Eagle, doing that more complicated.  I believe with your program, it is relatively easy, and the procedure is described on the vendor's site.

If they are not "ground" and there is a ground pour, there will be an isolation ring around them.

Here's an example of a similar application in which I use the USB for power :


Note, they are included in the ground pour.

 

Offline fourfathom

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Re: First PCB for a beginner, where to start?
« Reply #29 on: July 31, 2021, 05:26:33 pm »
Here's the USB-C layout (KiCad) I mentioned above:
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Offline JLynchTopic starter

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Re: First PCB for a beginner, where to start?
« Reply #30 on: July 31, 2021, 06:28:43 pm »
Thanks for the help with the grounding question and the pictures you guys sent. Kind of figured the USB shell should be grounded just didn’t understand why EastEDA was complaining and honestly still confused about how it handled things.

There was just no way to clear the DRC error when adding USB grounds to the PCB and keep the rest of the layout work I had done. No matter what I did EasyEDA wouldn’t allow any traces to be added / connected between the metal USB shell and ground. The only way to clear the DRC errors was to scrap the PCB layout and regenerate it from an updated schematic with grounds already added to the USB shell.
 

Offline admiralk

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Re: First PCB for a beginner, where to start?
« Reply #31 on: July 31, 2021, 06:37:29 pm »
No option to just update from schematic?
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Offline jpanhalt

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Re: First PCB for a beginner, where to start?
« Reply #32 on: July 31, 2021, 08:02:58 pm »
@JLynch

If your are sure everything is ok, but EasyEDA still puts a track where you don't want it, with Eagle, you can rip the track up (i.e., convert to airwire) and make your Gerbers.  I don't think airwires are included.  If worried, just hide the airwire layer.
 

Offline JLynchTopic starter

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Re: First PCB for a beginner, where to start?
« Reply #33 on: July 31, 2021, 10:26:56 pm »
Way new to all of this but couldn’t find any option to ‘Renew’ layout from the schematic, sure does sound like a nice feature to have though. As for deleting or turning the unwanted trace into ‘airwire’ wasn’t really the problem. EasyEDA appeared to have created a rule that prohibited a trace from being connected to the USB shell and any attempts to do so were blocked. So while deleting the unwanted trace worked it brought up the DRC error, and trying to lay down a new trace was impossible. Again first time out with all of this so there’s a ton of stuff I could be missing or simply don’t understand.

Schematic and PCB are done and sent off to JLCPCB, 5 boards, 2 assembled including shipping $34.00. Right now waiting for design approval and the estimate says I should have them in 4-7 business days.

Actually the $34 dollars was a second round go at submitting the PCB, the first try was closer to 50 bucks which is when I learned the importance of using ‘basic’ parts whenever possible. Swapping out a couple of the Extended items brought the price down considerably.
 

Offline tooki

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Re: First PCB for a beginner, where to start?
« Reply #34 on: July 31, 2021, 11:41:20 pm »
To me, using the datasheet for measurements is obvious, so you need to spell out for me what the alternative to be avoided is, because I can’t think of any.

Alternatives:
The KiCad libraries, SnapEDA.com, Ultralibrary.com, mouser.com/electronic-cad-symbols-models/, etc, etc.

If I use one of these sources I still need to check the dimensions.  I do build my own footprints from time to time, using the datasheet measurements.
:palm: Those are sources for footprints, not measurements.

And this much earlier reply of mine clearly makes obvious that I understand the concept of (and pitfalls of) premade footprints:
While drawing schematics in EasyEDA seems quite straightforward I’ve found selecting components rather confusing, perhaps I’m going about it the wrong way.
It has the double-edged sword of user-created component symbols/footprints. On the one hand, it often makes it a lot quicker to find what you need, especially for the components favored by hobbyists. The downside is that the symbols/footprints may not be well drawn. (Though errors  happen on manufacturer-provided in symbols/footprints, too.)

I strongly suggest learning to make your own footprints, as it's often faster than hunting down the right one and carefully verifying its correctness. EasyEDA's symbols will be fine for jellybean parts, though, and their SMD footprints are well-made and follow a careful naming system, so even if you have to make your own symbol, for most things you can use an existing footprint.

My question was “what sources of measurements (not footprints!) are there other than the datasheet?”, since the claim as written was to stop looking “beyond the datasheet for measurements”. (It wasn’t “stop looking beyond the datasheet for footprints.”)
« Last Edit: July 31, 2021, 11:52:54 pm by tooki »
 

Offline tooki

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Re: First PCB for a beginner, where to start?
« Reply #35 on: July 31, 2021, 11:44:54 pm »
@tooki - Now I understand your confusion. I think two thoughts were running trough my head when I typed that. It should have been simply,
Quote
It might seem a pain at first, but after making a couple you will stop looking past the datasheet.
And as fourfathom pointed out, the alternative is to search for prebuilt patterns.
If, as it seems, you mean simply “I always draw my own footprints from the dimensions in the datasheets instead of using premade footprints”, why not just say “I always draw my own footprints from the dimensions in the datasheets instead of using premade footprints”?!?

So with that in mind, I remain just as puzzled by your original reply to me as in the beginning. I said I recommend drawing your own. You replied that I should “stop looking beyond the datasheet for measurements”. If you meant I should stop looking beyond datasheets for footprints, isn’t that just repeating what I said, except using the wrong terminology?!? (So why admonish me to do what I’m already doing?) And if that’s not what you meant, then my question stands: what sources exist for measurements (NOT PREMADE FOOTPRINTS) other than datasheets?!?

As Ms. Swan from MadTV always said: “say what you mean and mean what you say!” :P
« Last Edit: August 01, 2021, 12:08:44 am by tooki »
 

Offline tooki

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Re: First PCB for a beginner, where to start?
« Reply #36 on: August 01, 2021, 12:07:47 am »
Way new to all of this but couldn’t find any option to ‘Renew’ layout from the schematic, sure does sound like a nice feature to have though.
Of course it has it, that being a fundamental feature of an EDA program.

If you’re in the schematic, it’s Design > Update PCB (Alt+U)
If you’re in the PCB, it’s Design > Import Changes (Alt+I)
 

Offline fourfathom

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Re: First PCB for a beginner, where to start?
« Reply #37 on: August 01, 2021, 01:45:19 am »
:palm: Those are sources for footprints, not measurements.

I checked back a few posts, and you were responding to a question about footprints, and admiralk mentioned measurements -- meaning measurements of the footprint dimensions.  You then asked about potential sources for measurements.  I, and apparently everyone else, assumed you were still talking about footprint measurements.

If you want package dimensions, some of those sources I mentioned also have 3-D models, and sometimes these are quite accurate.  Sometimes they are more generic.
« Last Edit: August 01, 2021, 04:43:38 am by fourfathom »
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Offline jpanhalt

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Re: First PCB for a beginner, where to start?
« Reply #38 on: August 01, 2021, 09:36:06 am »
Footprint versus measurements seems almost a distinction without a difference.  When in the "footprint" (aka package in Eagle) editing mode, every line,  pad, or feature will have the coordinates and usually dimensions available (e.g., dimensions of a pad are given as well as its coordinates).

It is really quite simple to convert those coordinates back to dimensions; however, when I edit or draw a footprint, I often use the coordinates for accurate positioning.  For example, assume you have several pads to place symmetrically around a chip.  It is easy to do with the grid or by coordinates as the coordinates are to the center of each pad.  Moreover, when one imports a "footprint" as a DXF file, you can align it using the grid or in a single step using the coordinates and a command line.

In fact, there was a recent thread here asking why used dimensions at all: https://www.eevblog.com/forum/chat/do-tables-of-xy-coordinates-tarnish-the-souls-of-engineers/msg3487310/#msg3487310   
 

Offline fourfathom

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Re: First PCB for a beginner, where to start?
« Reply #39 on: August 01, 2021, 03:16:30 pm »
Since tooki was getting all frustrated with our replies, I suppose that he/she was actually asking about package dimensions.  Yes, the terms are fairly non-specific.
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Offline tooki

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Re: First PCB for a beginner, where to start?
« Reply #40 on: August 01, 2021, 08:13:08 pm »
To me, measurements or dimensions means the sizes and distances and positions of things (in units like mm or inches), as typically found in the package drawing in a datasheet.

To me, in the context of EDA software (which this is) the “footprint” means the complete digital representation, in the EDA program, of the PCB features (pads, holes, etc) needed to mount the part.

One would use the measurements/dimensions/datasheet drawing to create the footprint in the EDA software.

The footprint is linked to the component’s schematic symbol so the software knows which signal goes to which physical pin.


My frustration with your (plural) replies is indeed because you both seem to be very, very, very sloppy with your terminology (and happy to be sloppy). Many terms actually are specific, which is why it’s confusing to others when you use them in a nonstandard way. (I worked for years as a technical writer, and one key thing in technical writing is to use terminology consistently and precisely. That means not using multiple terms to refer to the same thing, and not using the same term to refer to multiple things. This discussion is a textbook example of why this is a cardinal rule in technical writing.)
 

Offline jpanhalt

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Re: First PCB for a beginner, where to start?
« Reply #41 on: August 01, 2021, 08:26:29 pm »
@tooki

Troll.  I refuse to address it further.
 

Offline admiralk

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Re: First PCB for a beginner, where to start?
« Reply #42 on: August 01, 2021, 09:22:45 pm »
So with that in mind, I remain just as puzzled by your original reply to me as in the beginning.  ... So why admonish me to do what I’m already doing? ...

I was not replying to you. I was seconding what you said, and trying to add a little to it.
 

Offline tooki

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Re: First PCB for a beginner, where to start?
« Reply #43 on: August 02, 2021, 02:14:00 pm »
So with that in mind, I remain just as puzzled by your original reply to me as in the beginning.  ... So why admonish me to do what I’m already doing? ...

I was not replying to you. I was seconding what you said, and trying to add a little to it.
Oh. But you did reply to me, by quoting what I said.

In such cases, it’s wise to preface the reply with “I concur: …” or similar to make it clear you’re expanding on it. In context, it did not appear to be in agreement.


@tooki

Troll.  I refuse to address it further.
It’s your prerogative to not discuss it further. However, “trolling” has a specific meaning, and even heated discussion does not constitute trolling. Trolling means to be deliberately offensive and provocative, for the purpose of creating artificial discord. Frustration at a very real misunderstanding does not constitute trolling, so it’s unfair to make such a false accusation.
 


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