Hardware Reference
In-Depth Information
The
design phase
is just the flow of going back and forth between generating and test-
ing ideas that naturally occurs while building something.
Designing
is often done on paper
or in a computer simulation, and
prototyping
is always physical. The design process is al-
ways iterative, but it's not a chicken-and-egg scenario. Your first
design input
is always
your formal definition. Every successive prototype you build (whether it works or not) is
considered a
design output
.
The way you iterate during the design phase is by checking
whether your prototype meets the requirements listed in your product definition. This of-
ten-neglected step is called
testing
(or sometimes
validation and verification
)
. Of
course, design doesn't occur in a vacuum, and no one ever perfectly defined the scope of a
project before starting to work. Lots of different design inputs may emerge while you're
in the middle of working, whether it's something you failed to consider during the defini-
tion phase, a critical part that happens to be made of
unobtanium
(an unobtainable part),
or a problem you learned about only during testing. We'll get into how to handle those
new needs in the next bit.
Once your design meets all of your critical requirements, you can launch into the
re-
lease phase
.
During release, you start with your final preproduction prototype that's prac-
tically perfect in every way, and test it to the point where you have decided that you are
ready to commit—that is, this exact version of the product is what you will sell to custom-
ers. Once you're in release, change
ist verboten.
All you should do during this phase is
double-check the technical and ephemeral details for your project one last time and make
sure that this version of your design is
the one.
In the event that you catch a bug and need to change any part of your design that isn't
something cosmetic (such as silk-screen color), then you need to think long and hard
about the best way to fix it. If it's a major design change (and not, say, buying a different
0603 1k resistor to use), you absolutely need to stop where you're at, go back to the
design phase, and make another preproduction prototype. Then start the release process all
over again. This process may seem tedious, but the release phase is your last critical check
to make sure you've caught everything before you commit a huge amount of time and
money to go to
manufacturing
.
Any last-minute, unchecked detail in design or
something you've forgotten to check in testing can become a serious risk once manufac-
turing is involved. (If you don't believe me, check out Matt Bolton's chapter on manufac-
turing,
Chapter 12
,
Accelerate from Making to Manufacturing
.
) Once you
honestly
feel
there's no way your project can possibly fail, then and only then do you hit the big red
button and release your design to production.
Figure 5.1
shows the process that industry follows (or should follow) for many
products that have made it to market. There are different versions for different industries,
and this example was adapted from the FDA's
Design Control Guidance for Medical
Device Manufacturers
because medical regulatory approval is incredibly strict and tries to
