There have already been lots of replies, but I'll throw in my few
comments...
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Hi,
Upto now I've been building simple little projects on breadboards.
Now I'd like to try my hand at designing a pcb board with an MCU
onboard
and all.
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Do you have any actual layout tools in mind? Although they all require
the same basic skills, they all differ in implementation and difficulty
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I have a couple of questions which have puzzled me.
1) Is the board designed first and then the software written for the
MCU
or is it the other way around. I had one old school electical engineer
tell me the board is designed first whereas I thought the software and
circuitry is prototyped in pieces first and then comes the completed
schematic layout.
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In a perfect world (rarely realised) the board requirements are stated
first (Someone mentioned a project manager - that's one option). If the
requirements of the board are clear, the electrical design requirements
are at least clearer. As noted, unless the board is for a single
purpose or perhaps just a general purpose (with I/O connector
positions, for example) it is *never* a good idea to try and design the
board without knowing what the software must do.
Often, all the design functions (electrical, firmware software, layout)
reside in one person. I don't know many electrical engineers who have
not written significant amounts of code - they *want* to know what the
code must do.
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2) How do board level designers (who may not know much about
programming
the MCU) know HOW to layout the board? Do they just look at
application
notes from the manufacturer and lay things out and get it right on the
first shot!?
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It is the task of the electrical engineer to guide the layout person
(who may in fact be that same EE). We do schematic capture (with lots
of notes), generate netlists and footprint requirements and pass them
to the layout person with our notes. It is not unusual for the EE to
sit with the layout person to deal with 'special' areas of the board.
As to HOW to lay out the board - practise, practise, practise. A
healthy does of aptitude helps, though.
We don't just 'look at app notes', although that forms part of the
design exercise. App notes live in a perfect, isolated world. We design
their parts into a larger scheme, which requires us to know how to
adapt the information in the app note to our current requirements.
As to getting it right first shot, that takes a lot of practise (luck
helps) and is usually a function of the complexity of the board,
although classic neophyte problems abound for even the simplest of
units.
I had 5 in a row completely correct (i.e. the prototype is the shipping
unit) for very complex boards (varied between really small and tight to
big and hairy). That's the exception although we always try to get it
right. It's the gotchas (which is why you should read the datasheets
and app notes thoroughly) that catch you.
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3) Is it possible that a board level designer can layout a board
without
knowing anything about programming the chips onboard?
::
If you are talking about the electrical designer, I would say *no*
except for the simplest of devices. All newer processors and
controllers have multi-use pins in these days, and a thorough knowledge
of what the code/system requires is necessary to assign the correct
pins to the correct board functions.
If you are referring to the PCB layout person, then they don't
necessarily have to know details, although we have to convey rules
about the circuitry (which could be high currents, fast transients,
high speed systems etc).
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4) For surface mount chips (not in a DIP format where you can plop it
into
a breadboard for trial purposes), how do you go about trying them out
before actually committing them to be produced on a PCB?
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Others mentioned making a prototype board first - I have done that
myself. On other cases, the SMD board *is* the prototype. For complex
boards (or for analog sensitive boards) two different layouts will
yield two different results, for an identical netlist.
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5) When you want to incorporate a chip into your design and hook it
upto
other chips onboard, what is the first thing you go searching for? The
datasheet or...? How can you be sure it will work in harmony with
what's
already onboard (i.e. all the pin connections are correct)
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The datasheets, application notes, tecchnical articles from the device
manufacturer. I also call the local FAEs to see if they have reference
designs.
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I got a few more questions but I'll stop here for now.
Thanks
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No problem
Cheers
PeteS