On Sun, 21 Sep 2003 14:24:05 -0000, Dave Mucha <
dave_mucha@...>
wrote:
> Hi all,
>
> I was wondering it there is an introduction to basics of schematics and
> board design?
>
> Things like what polarity is the square pad on an LED ?
> Why 15 mil traces and not 12.5 mil ?
> how to best isolate an AC rectifier/cap from the rest of the DC on the
> board ? things like that.
>
> are there 'standard' drill sizes that are common for all board houses ?
>
> I have a friend who says all square pads on 2 pins are ground or
> negative. Is that rule of thumb or general industry practice ?
>
> and it seems a 90 degree corner on a 15 mil trace, when etched can be
> undercut to less than 10 mil.
>
> Instrumentation inputs may be put inside of a ground ring to as to keep
> all stray baord voltages away.
>
> Seems I went to the monkey-see monkey-do school of board design.
>
> Dave
>
>
>
you can design all these things like you want them.
like it makes best sense for you.
track with is determined by current/voltage drop you can accept.
but in many cases the voltage loss due to resistance is so little that you
rather make it as small as your design process allows to be manufactuered
securely. (if you have lots of space make it wider).
further you for sure will not calculate the minimum with for each track,
you simply take "standard with"
0.3mm or so what you like and only the tracks which are higher current
(maybe supply etc.) you make thicker.
the sqare pad is pin 1 most cases. never thought about cathode/anode on
diodes. i leave it how the pcb software
makes it.
i don't understand what you mean with isolate the rectifier part...
standard drill sized i don't know because i drill myself.
but 0,6mm, 0,8mm, 0,9mm, 1mm, 1,2mm and maybe 0,4mm if you need i am sure
any boarhouse in europe offers.
0,85 and 0,95 too.
If you can choose than you select the drill for the wire thickness
(emphasis on tolerances!).
ground rings around opamp inputs work. but there is also "guard ring".
it puts the "ring" or coax shielding not at ground but on a voltage which
is the same like the one measured (but low impedance).
this way you get zero losses from bad insulation etc. because there is no
voltage differential thus no current flow.
some opamp have special guard output but you may often use the other input
if it is low impedance.
(remember in amplifier configuration the inputs are at nearly same voltage)
.
monkey-see, monkey-do is not the worst way.
but monkey always should know why he does things.
only doing things for no special reason only because somebody else did it
is not good.
it may be not adequate for the situation.
st
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