"Retro Repair" key electronics skills?

tony duell ard at p850ug1.demon.co.uk
Tue May 10 14:39:36 CDT 2016

> My father is a civil engineer.  When I was a little
> kid, he was in the US Air Force.  We would frequently
> go to the runway snack bar, get ice cream and watch
> the B-52s do "touch-and-go" landing practice.  The
> plane's wings would "flap".  It raised the hair on
> the back of my neck.  My dad explained that, if they
> didn't flex, the wings would break off.  After a
> while, I understood, intellectually.  It still "gave
> me the willies".  Later I had a similar experience
> when I was with him in a tall building and realized
> that it was "waving in the wind".  Same thing, if it
> didn't flex, it would fall.

That reminds me of the following joke : 

There is an airline passenger. During some particularly
turbulent conditions he looks out the window and sees
the plane's wings flexing. He looks very worried.

The flight attendant comes over to him and tries to
comfort him by saying

'Our pilots are fully trained to fly in conditions like 
this. It's only turbulence, it's quite normal'

He replies

'You don't undertand. I work for Boeing. I am one
of the men who designed this aircraft. The wings
are not supposed to flex like that.'

> > The other is that, as I said before, any ground
> > connection has impedance (it's the inductance that
> > is troublesome normally) so that points (say IC pins)
> > that are shown as grounded may actually have a
> > voltage difference between them.
> If I think about it too much, this gives me the
> willies, the same way.

It's a very real problem, it's the main reason for
decoupling capacitors which provide a local
source of power with a low impedance connection
(as they are so close to the IC). 

That's why I said that most times the interconnections
are the hard part of a digital circuit.


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