[sdiy] Block based design was: Favourite VCO designs

[Scott Nordlund]

> David,
> it's indeed very useful to break up your designs into blocks and this
> happens in every discipline of engineering. Plumbers have their
> different pipes, software engineers have functions, electronics
> engineers have their functional units, production/processing engineers
> have their what-have-you.
>
> However it's not good to think of them as completely separate blocks,
> since they can often negatively affect or even interrupt each other's
> operation:
> - an air bubble two stories above can make my tap make squeaky noises
> when it's used
> - two functions in a computer program could be interacting through side-effects
> - two blocks in electronic circuits could be interacting through the
> power supply
> - two processing machines standing next to eachother could be
> exchanging heat creating unwanted feedback in the control problem


Electronics design critically depends on the ability to break things
into individual blocks.  Aside from software simulation, it quickly
becomes totally unworkable to analyze or design anything of useful
complexity when the entire circuit has to be considered as a whole.

Of course an actual circuit doesn't really have isolated 
subsections, or even well defined inputs and outputs, and isn't 
really separate from the rest of the universe.  BUT any workable
design process must pretend that this is the case, and it generally
works out pretty well.

Power supplies are regulated and decoupled, inputs and outputs are
buffered, cabinets and cables are shielded.  Thus your synth patch 
will sound approximately the same regardless of the freshness of 
the milk in your refrigerator, and doesn't depend a great deal on
the phases of Jupiter's moons.  These things, being a part of the 
same universe, are interacting, but not in any meaningful or 
measurable way.  

Well this doesn't always work out perfectly.  Older electronics 
with less "ideal" components (vacuum tubes, etc.) don't conform so
well to this, sometimes with noticeable effects.  But I can assure
you that these things weren't a part of the design process.  And 
it's a total crap shoot whether this makes a positive or negative 
contribution to the end result.

The solution?  Yes, absolutely think of things as completely 
separate blocks, and design them so that they will stay that way.
Of course there is potential for unanticipated effects, and we 
must be prepared to deal with them, but with a decent design
process there's no need to invoke that sort of thing on a 
regular basis.
 		 	   		  
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