The Art of designing PCB boards

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As a weekend DIY Electronics Hobbyist I am starting to get more and more involved with creating PCBs for my useless projects wink. As my little projects start to get more and more complex, creating the PCBs becomes more like a puzzle rather than electronics. Trying to figure out how to layout all my 'vias" can be time consuming. I give a lot of credit to someone who does this full time. A simple 2 layer layout can take me hours (days sometimes) to develop. So developing PCBs is both fun and a challenge. I am curious if any other people struggle with PCB design.

"When all else fails, read the directions"

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Yes

 

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Invest for cash flow, not capital gains!

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Absolutely! Simpel boards also takes me a long time cause I like to have as little traces in the ground plane as possible and yet keep the board as small as possible cause its cheaper :). I go crazy sometimes...

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I always like laying out the PCB.  As you mentioned, it is both challenging and rewarding.

 

The Pro's have mocked my simplistic approaches a couple of times, but I'll share a few thoughts I try to keep in mind:

 

I generally make two sided PCBs.  This is a lot less work than trying to route a single sided PCB, although if it is a small, simple project, and you are making your own boards, then single sided might be a reasonable option.

 

I then try to route one side's traces North/South, and the other side's traces East/West.

Only when I am about done, and routing the last couple of traces that are somewhat problematic to route, do I willingly violate this rule.

 

Route your power buses first, and use large traces.

 

Be sure to put mounting holes on the PCB.

 

Be sure to mark Pin #1 on chips and Headers!  Although the PCB copper pattern may have a square pad for Pin #1, you won't see that once the parts are installed.

Sometimes I mark them in copper, sometimes I mark them with the silk screen.

 

I usually route the Xtal, its caps, and By-Pass caps early on, as I want them adjacent to specific pins.

Technically an external Xtal should have its own Ground Pad under the Xtal, and no signal lines running under the Xtal, on either side of the PCB.

I've often omitted the ground plane under the Xtal without it causing problems.

 

If you are using the ADC or DAC then be sure to use a different Ground bus/plane for the analog circuitry, and AVcc.

Connect this to the digital Ground at only one point, preferable near the power supply source.

 

Make your traces wide.  Your not routing a PC motherboard!

 

I route any unused uC I/O pins to spare pads.

If I need to add something to the PCB, or do a little surgery on the PCB later on, this makes it much easier.

 

I don't etch, (or whatever), my own PCBs, and when you get them made the incremental cost to get a few "extra" PCBs is usually very small.

So it is worth getting a few extra PCBs.

You can then use them as you experiment and tinker in the future, often with a few modifications as needed.

But the core uC layout, programming header, power supply, etc, are all already on the board.

 

I usually route V+ and Ground to a couple of extra pads, often to a 2-Pin header.

This is useful for checking the Power rail as one eventually installs component, and for monitoring the power rail, if needed, during debugging.

The Ground pin is also useful for connecting an O'scope probe, (or Logic Analyzer).

 

If you have a spare I/O pin then route it to a resistor and an LED.

If you use JTAG to debug than that probably isn't necessary.

I use and LED and sometimes an LCD to debug, and having a spare LED is nice.

If you want to see if your code reaches a particular ISR you just turn on the LED inside the ISR routine.  Easy.

One can also put a scope across the LED and Ground as use it as a scope trigger for timing events, ISR durations, etc.

Just turn on the LED whenever you want to trigger the scope.

 

Be sure to put a project name / title, and a version number, and a date on the PCB.

Over the years it will be helpful as you collect PCBs to rapidly identify one you want to work with.

Also, if you make a later revision to the PCB, it will be important to know which version you hold in you hand without having to track down specific traces and changes to identify it.

 

Remember, too, that you can install pads for extra components, but you don't have to install them on the PCB.

An example might be the pads for an external Xtal and its caps, or for an RC low pass filter for a PWM output.

 

I usually put a 2-Pin Vtg Header on the PCB, also, to either connect, or not connect, the PCB's Vcc to the Vcc pin on the 6-Pin ISP programming Header.

Some programmers, like the AVR ISP mkII, require the target's Vcc to be present on the programming Header.

They use it to set the programming signal level, and to insure that the PCB is powered.

 

Other programmers, like the STK500, can optionally SUPPLY power to the target PCB through this pin.

You don't, however, want the connect the STK500's V+ supply to the PCB's V+ rail if the PCB has its own supply.

 

Obviously, projects that are well defined, single purpose, or intentionally small, don't need a lot of the above.

But as primarily a hobbyist I find the "old" PCB's often get hacked for a future project, or quickie experiment, and the above are beneficial.

 

JC 

 

Last Edited: Sat. Jan 24, 2015 - 12:11 AM
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I use a program suite called DipTrace.  It has an autorouter in it that works pretty good for most things, although I always check everything over afterwards.

 

They have a freeware version that is the full suite, and allows you to make unlimited size schematics, and pc boards to 300 pins which should be more than enough for your needs.

 

Just something you might want to explore.

 

 

www.diptrace.com

 

 

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

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Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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Philly,

 

DocJC has some very good suggestions, some of which you may have already "discovered" through experience. I would add that "we" should also consider the placement of components relative to the others with respect to the ease of assembly and the order of that assembly. For example, a large electrolytic capacitor could block access to the pins on one side of a smd chip, or prevent you using a blade to lift a DIL component out of its socket. I start with a rough idea of the space need for all the components and then their relative placement with respect to any human interactive items such as displays, push buttons, connectors, etc. I then select an enclosure and the first items I place on the "blank pcb design" will be the mounting holes.

 

Personally, I enjoy the "puzzle" of trying to do single sided pcb designs with few if any jumpers. I also like solving Sudokus in my head. (Yes "it takes all kinds.") I etch one offs and proof of concept prototypes myself. I find this is faster and cheaper in most cases. After testing I go to commercial producers. Although many will disagree, I regard this effort as part of the whole deal... a little like walking the whole journey instead of just going directly from the start to the destination without the nice walk in between.

 

Whatever method you choose, don't rely upon autorouters. Use your own brain. The more you use it the better you will get.

 

Cheers,

 

Ross

 

Ross McKenzie, Melbourne Australia

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PhillyNJ wrote:

As a weekend DIY Electronics Hobbyist I am starting to get more and more involved with creating PCBs for my useless projects wink. As my little projects start to get more and more complex, creating the PCBs becomes more like a puzzle rather than electronics. Trying to figure out how to layout all my 'vias" can be time consuming. I give a lot of credit to someone who does this full time. A simple 2 layer layout can take me hours (days sometimes) to develop. So developing PCBs is both fun and a challenge. I am curious if any other people struggle with PCB design.

+1

 

Some boards took several days. I always try to squeeze in too much. Don't know why .... cool

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<RANT>

What I find frustrating is bossmen who like to deploy you on other (non-PCB) projects sporadically so that you have to work out what you were doing when you got diverted and causing the design of small, simple boards to take forever to finish. Of course they then have no qualms about grilling you about why its taking so long.

</RANT>

 

Steve

Last Edited: Fri. Jan 23, 2015 - 11:38 PM
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schtevo wrote:

<RANT>

What I find frustrating is bossmen who like to deploy you on other (non-PCB) projects sporadically so that you have to work out what you were doing when you got diverted and causing the design of small, simple boards to take forever to finish. Of course they then have no qualms about grilling you about why its taking so long.

</RANT>

 

Steve

 

Steve. I understand.

 

I had a Saudi official who expected a very detailed and complicated analysis of airport heights to be finished by me overnight and could not understand why I said it wasn't possible, until... I asked him if he could read the Koran from start to finish. Of course he said yes. Then I asked if he could do it overnight. I was then given the two weeks that was needed. You need to find something that they can understand... like why it is taking the bossmen so long to pay your invoices.

 

Cheers,

 

Ross

 

Ross McKenzie, Melbourne Australia

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don't rely upon autorouters

I DID say I check everything afterwards didn't I?

 

Use your own brain

Yes, and that's why I use the autorouter wink

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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Designing a pcb involves solving conflicting requirements - physical, electrical, mechanical. Switched supplies seem to give me the most grief - getting them quiet is a challenge.  The Doc's method of north,south, east and west worked well on through hole designs, but tends to fall down when doing surface mount - a tqfp just doesn't want to play ball!

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a tqfp just doesn't want to play ball!

What about a ball grid array chip?

John Samperi

Ampertronics Pty. Ltd.

https://www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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I use double sided boards and don't make them myself.

 

I run east-west on one side and north-south on the other, as much as possible.  Otherwise the planes get broken up a lot.

 

I agree with most of DocJC's suggestions.  I always put a little LED (like 0603) on the board that flashes at around 1 Hertz.  It is driven by a real task via the task switcher and is triggered by an RTC interrupt.  A quick glance at the board will tell me if the "system" is working.

 

I always start with a schematic.  I run a program often that compares the schematic with the PCB to make sure I'm not making mistakes.

 

I don't use an autorouter and actually don't have one with the software I use.  I don't find it much of a problem running traces though.

 

Wide traces are good but unless they supply lots of current they are usually impossible for me.  If you use QFN chips with a pad pitch of 0.5 mm, you'll know what I mean.

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A simple 2 layer layout can take me hours (days sometimes)

The "Freeduino" PCB design took about 2 months... http://www.freeduino.org/freedui... I would not call it a complex design.

(That WAS with ~4 geographically dispersed "hobbyists" working in their spare time and worrying about "esthetics" as well as design, and it did produce four different boards.)

Hours to days is nothing!

 

*Removed trailing space from link. Ross*

 

Last Edited: Sun. Jan 25, 2015 - 05:55 AM
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I tend to make 2-layer boards, starting with the positive rail on the top and the ground rail below. Then topside running NS and bottomside running EW (or vice versa, depending on chip layout and size).

 

The net result is that the ground planes (recall that to AC, the rails are attached together) tend to get broken into long fat strips, but still maintains a solid plane as far as possible. This design doesn't actually show the planes, but basically everywhere it's black, it'll have a plane on both sides. Perhaps a couple of weeks of evenings...

 

 

Neil

 

 

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I support your suggestion.

 

*A warning PM was sent hours ago. Ross*

OURPCB Tech(www.ourpcbte.com) provides PCB design, PCB and PCB Assembly

Last Edited: Mon. Jan 26, 2015 - 02:04 PM
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barnacle wrote:

 

 

 

Neil

 

 

 

Ok Neil - looks nice - what is it (purpose/function)? wink

"When all else fails, read the directions"

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It looks like something that would hang in a modern art gallery.  I'd call it "Repetition with ugly colors".  smiley

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Maybe it's a Piet.  Or a Piet.

"Experience is what enables you to recognise a mistake the second time you make it."

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steve17 wrote:

It looks like something that would hang in a modern art gallery.  I'd call it "Repetition with ugly colors".  smiley

 

But why all the holes? Go SMD

 

*Duplicate deleted. Ross*

If you don't know my whole story, keep your mouth shut.

If you know my whole story, you're an accomplice. Keep your mouth shut. 

Last Edited: Mon. Jan 26, 2015 - 11:39 PM
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Torby wrote:

 

But why all the holes? Go SMD

Do they make SMD nixie tubes?smiley

Last Edited: Mon. Jan 26, 2015 - 10:34 PM
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Don't think anybody makes nixie tubes any more. You have to find them in old Soviet stock piles or old HP frequency counters. As a kid I loved watching them count as the numbers moved forward and back...

If you don't know my whole story, keep your mouth shut.

If you know my whole story, you're an accomplice. Keep your mouth shut. 

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I think I design my boards when I draw the schematic.  I use a 44 pin Xmega these days.  I make a square to represent it.  I put the pins in the right place, 11 on each side.  I label the pins so I know what their function is.

 

I put the parts that connect to the Xmega  near the Xmega pins they connect to.  The USB pins are on the right side, so I put the USB connector on the right side.  The PDI pins are at the upper right, so I put the header there, etc..  Then I draw wires to connect the pins in the most efficient way, with as few crossovers as possible. 

 

Then I plop down the Xmega footprint on the board.  Then I put the parts that connect to it near the Xmega pins, like I do with the schematic.  Then I draw traces to connect the parts as efficiently as possible.  I use ExpressPCB.  If I click on a pad, it will highlight all the other pads it connects to.  That's about all the help we used to have. 

 

Then, a couple of years ago, a fellow named Marty Flick came along and wrote a kick-ass program called xCheck.   It compares the schematic with the board and tells me if there are any errors.  It also does a DRC and tells me if there are any violations.  If xCheck finds nothing wrong, I am confident the board is good.  xCheck never failed me yet.  I suppose other board design programs can do this, but I think not all of them do.

 

Here's part of my Xmega schematic.  It's not pretty, but it works for me.

 

 

 

                                   

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I make a square to represent it.

??? You put the COMPONENT down from your library not a "square" wink  The component(s) will then export from the schematic to your PCB package and the tracks will be at the correct place even if just as "rubber bands".

John Samperi

Ampertronics Pty. Ltd.

https://www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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Obviously you don't use ExpressPCB.  There aren't many "components" that come with the package.  I made that "square" and I'm proud of it.  wink  I also made the QFN44 footprint.

 

There is nothing in the libraries that relates schematic components with footprint components.  The "libraries" are just O.S. folders.   I have to put the footprints on the board.  The footprint is related to the schematic symbol only after I assign them the same component ID.  Even then it doesn't draw the traces automatically.

 

But the software is free and seems easier to learn and use than others I've tried. 

 

Actually my xmega schematic isn't quite square but might look that way if you viewed it from an edge.  smiley

 

 

Last Edited: Tue. Jan 27, 2015 - 10:30 PM
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It was a possible layout for a 65c02 single-board computer, a throwback to the seventies. Which is why the holes and big components; making it small can happen any time... the ugly colours are free of charge with Eagle.

 

Quite why the image is reversed I have no idea, but it is. It's probably something to do with quantum.

 

Neil

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PCB

 

 

 

while(!solution) {patience--;}