design process advice

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hello
i need advices from any experienced people here...
if you have a microprocessor-based embedded system board (sbc like),
you got design on schematics (but you dont know if it's going to work,
because it's on paper only and you can't test it), how do you validate
the design before you send it to pcb manufacturer for prototype?

also, can you tell me what the basic procedure involved in designing
embedded systems, like from sketch, component wiring, etc, until
production?
and is there any way we can save money by avoiding mistakes before
sending it to pcb maker ?

Re: design process advice
hello
i need advices from any experienced people here...
if you have a microprocessor-based embedded system board (sbc like),
you got design on schematics (but you dont know if it's going to work,
because it's on paper only and you can't test it), how do you validate
the design before you send it to pcb manufacturer for prototype?

also, can you tell me what the basic procedure involved in designing
embedded systems, like from sketch, component wiring, etc, until
production?
and is there any way we can save money by avoiding mistakes before
sending it to pcb maker ?

Re: design process advice
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You build a breadboard.

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My old boss used to say 'The only people not making mistakes are those
who are doing nothing'

Ian


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Re: design process advice
On Fri, 25 Jul 2003 11:31:53 +0100, Ian Bell

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[...]
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Experience will help you avoid mistakes .

You gain experience by making mistakes and learning from them...

Regards,

                               -=Dave
--
Change is inevitable, progress is not.

Re: design process advice

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If you are copying from a development board, make sure you've copied
accurately. You might be able to try things out with a breadboard or
lash something up with matrix board. Go to someone cheap (PCB Pool,
Olimex etc.) for the prototype and assume that you are going to get
things wrong before they come right. That's going to happen if you are
inexperienced anyway, and probably when you are experienced too.

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Blag what you can from reference designs. Read the data sheets and app
notes very carefully. Think carefully about layout: you need a good low-
impedance power supply system, where switching in one part won't cause
glitches in another part. Think of where the return paths for signals
(esp. high speed ones) go. Make sure bits that don't belong together are
separated, electrically as well as physically. Have a good CAD system.
Keep your notes up to date. Have someone handy to explain every bit of
the circuit to as you go along... there's nothing like saying it out
loud to expose the fatal flaw in the best laid plans.

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Check what you are doing, how it works, and how you've implemented it
very carefully indeed. You might actually SAVE money by getting a
prototype fairly early to make sure the concept works... nothing worse
than finding the big misconception a week before you are due to
demonstrate a working unit to the customer.

Paul Burke



Re: design process advice
Saving money on a PCB is quite easy these days - we just had the pleasure
using www.olimex.com .... 99-USD for two prototype boards - shipped with
Fedex overnight.

If your schematic is made - and the most important sub parts of the circuit
have been carefully evaluated (e.g. bread boarded) ..... hit and trial - the
first PCB will never be perfect anyway. Make sure you surf for  hints on PCB
design before the layout is done.

Kristoffer



Re: design process advice
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I use some manufacturers in Brazil:

Digicart - snipped-for-privacy@digicart.com.br ($66 for 5 prototype boards)
Micropress - www.micropress.com.br (more expensive, but makes multi-layer boards)
PCI - www.pciparana.com.br

Re: design process advice

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Verification of the design could be achieved in 3 ways either in
combination or in isolation.

1. Simulation
2. Prototype
3. Peer review.

Each method has a limited scope of coverage and each have associated
pros & cons.

Typically the engineers at my work, go from schematic->PCB layout->
straight to copper. From experience they have found that breadboard
prototyping is a waste of time. Particularly if you're using some
inferior medium like Veroboard or similar (talking about micro designs
here). One seems to be debugging the breadboarding rather than the
design.

So the only verification done at my work is design review of the
schematics and probably a sanity check on the PCB layout. Also (if
possible) plan (in time & budget) for at least another interation of
the board.

To perform a proper review, the reviewers must:
a) Be in a correct frame of mind & had inspected the circuits prior to
the review meeting. There's nothing worst than going into a review
meeting and having the reviewers only just viewed the design. All
participant must be familiar with the material in question prior to
the meeting. If this is not the case, then reschedule the meeting
until everyone is better prepared.
b) Setting out a clear & concise list of criteria. Throwing a circuit
at an engineer & saying "Here, check this" is not the right approach.
Possibly each review member should be given a particular task such as
checking the supply rails & current consumption or checking that all
unused inputs are tied low, for example.
c) Reviews should NOT be confrontation or "slinging" matches. The aim
of the review is to expose errors in the design. Although difficult,
"style" should be removed from the agenda or better still have style
issues be part of a company guideline, so that there won't be any
disputes.
d) The convenor of the review should be strict & keep the discussions
in scope.
e) "Share the responsibility". Have reviewers sign-off a Review Sheet
-- having people put their signature on a piece of paper is always a
reality check.

Experience is invaluable and the use of prior designs which have been
tried & proven is a plus.

Ken

+====================================+
I hate junk email. Please direct any
genuine email to: kenlee at hotpop.com

Re: design process advice
On Tue, 29 Jul 2003 06:59:05 GMT, snipped-for-privacy@noname.com (Ken Lee)

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Good advice.  I can't breadboard my 357-pin BGA processors, so things
need to get reviewed frequently.  Get the symbols reviewed for pin
accuracy, get the schematic reviewed before release to the layout guy
and get the layout reviewed before it goes to the PCB house.

When building the first prototype, build it in sections.  Place the
power supply, processor and memory down first.  Then fire those up
slowly, and keep an eye on the current meter.  Magic smoke is
precious....keep it in the part.  Add another circuit, and keep going
until you get the whole thing together.  If you are new to the
process, you will probalby have to kludge stuff together.

Elroy



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