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'[EE:] How do you create and understand circuits?'
2007\01\28@154045 by Brooke Clarke

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Hi Lindy:

Sometimes when I look at a schematic it makes no sense at all.  But when
redrawn it becomes completely understandable.
I think that some schematics were drawn on purpose to obfuscate how the
circuit works or were drawn by a publisher to have a certain width or
height so they fit their page layout.  I recently was working with one
of these where the signal flow was like a book, i.e. left to right, down
a line, left to  right.  For me it's much clearer how it works if it's a
linear left to right flow.  Also using a lot of ground and Vcc symbols
removes lines that really have little meaning, leaving the important
stuff.  Sometimes I use a graphics software to color code schematic
lines which may help understanding.

The free Express PCB schematic drawing package makes it easy to draw and
modify a schematic.  It's often handy to make or modify the schematic
symbol for a component to simplify the schematic.  For example the input
pins to a PIC might be moved to the left side and the output pins moved
to the right side, with Vcc on the top and grounded pins at the bottom.  
This is much more understandable than having the pins in the same
relative location as on the actual part.  For logic parts where there
are multiple gates, each gate is a seperate component but they all have
the same ID such as IC4.

Recognize orders of magnitude.  Often part values are chosen so that the
impedance of the part is either very much higher than the adjacent
circuitry or very much lower.  Examples would be things like pull up
resistors or bypass capacitors.  Once you can see these parts you can
look past them to the more important stuff.

Often the data sheet for a component will have an applications section
that shows some typical circuits and will have an equation to help in
selecting a key part.  National Semiconductor is very good at this often
showing many different application circuits.

My computer has a folder called "data sheets" which has many sub
folders.  This is very handy both for figuring out existing schematics
and for designing new ones.  This is one area where the internet has
made life much easier than ordering hard copies of data sheets.

Have Fun,

Brooke Clarke

--
w/Java http://www.PRC68.com
w/o Java www.pacificsites.com/~brooke/PRC68COM.shtml
http://www.precisionclock.com

2007\01\28@160512 by David VanHorn

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>
>
> My computer has a folder called "data sheets" which has many sub
> folders.  This is very handy both for figuring out existing schematics
> and for designing new ones.  This is one area where the internet has
> made life much easier than ordering hard copies of data sheets.


Maybe some day, we'll get the ability to insert links into schematics and
source code.
Click here on the schematic to see the data sheet, click there to see the
definition of the pins on port B or the chip pinout in the source code.

2007\01\28@160742 by Kenneth Lumia

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From: "Brooke Clarke" <spam_OUTbrookeTakeThisOuTspampacific.net>
---- snip--------
> Hi Lindy:
>
> Sometimes when I look at a schematic it makes no sense at all.  But when
> redrawn it becomes completely understandable.
> I think that some schematics were drawn on purpose to obfuscate how the
> circuit works
----snip---------

Here's an example.  It takes a bit of time to figure out what
example 1 does,  but only a few seconds to determine the
function of example 2 (ignoring text on bottom).  Note they
are the same circuit.  Example 2 also gives clues about
what is "bad" about the circuit that can be inferred by the
symmetry of the schematic layout (unwritten).

Example 1: http://www.4qdtec.com/mvbz/mv1c.gif

Example 2: http://www.4qdtec.com/mvbz/mv1a.gif

Ken


2007\01\28@162252 by David VanHorn

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>
> Here's an example.  It takes a bit of time to figure out what
> example 1 does,  but only a few seconds to determine the
> function of example 2 (ignoring text on bottom).  Note they
> are the same circuit.  Example 2 also gives clues about
> what is "bad" about the circuit that can be inferred by the
> symmetry of the schematic layout (unwritten).
>
> Example 1: http://www.4qdtec.com/mvbz/mv1c.gif
>
> Example 2: http://www.4qdtec.com/mvbz/mv1a.gif


That's relatively easy.. I've seen much worse.. :-P

2007\01\28@163729 by Kenneth Lumia

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Yeah, me too.  This one was just easy to find!

Ken

----- Original Message -----
From: "David VanHorn" <.....dvanhornKILLspamspam@spam@microbrix.com>
To: "Microcontroller discussion list - Public." <piclistspamKILLspammit.edu>
Sent: Sunday, January 28, 2007 4:22 PM
Subject: Re: [EE:] How do you create and understand circuits?


{Quote hidden}

> --

2007\01\28@190219 by Dave Lag

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Kenneth Lumia wrote:

 symmetry of the schematic layout (unwritten).
>
> Example 1: http://www.4qdtec.com/mvbz/mv1c.gif
>
> Example 2: http://www.4qdtec.com/mvbz/mv1a.gif
>
> Ken
>

Often wondered,
Has anyone here become a "subscriber" of 4QDtec and did they consider it
worthwhile?

Dave


2007\01\28@192001 by Alexandre Guimar„es

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Hi, Dave

   I did quite a while ago..

   It was surely worthwhile, specially for the power circuits all made with
discrete components. Very nice information that is hard to find anywhere
else.

   I did not renew because I did not see much "renovation" on the
information.

Best regards,
Alexandre Guimaraes
> Often wondered,
> Has anyone here become a "subscriber" of 4QDtec and did they consider it
> worthwhile?
>
> Dave

2007\01\28@232907 by Dave Tweed

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David VanHorn <.....dvanhornKILLspamspam.....microbrix.com> wrote:
> There is a school of thought that puts pins on chips in a schematic in
> the same orientation as on the physical chip. Readability be damned,
> they are determined to make it easy to count pins. (like it was ever
> hard?) This procrustean solution to a non-problem results in gordian
> knot schematics that almost completely obscure the shape of the circuit.

I have to say that there's some merit in the idea. I do this on large
chips that have lots of general-purpose I/O, like microcontrollers and
FPGAs.

First of all, I don't like to create a custom schematic symbol for each
application of a part. Since most pins on these parts can be input, output
or both, there's no particular arrangement of pins on the symbol that's
obviously better than any other. However, there's a distinct advantage
to have them match the physical arrangement when you're trying to probe
the pins of, say, a PQFP to debug it, and so that's what I go with.

Of course, on specific-purpose chips that have definite inputs and outputs,
like logic gates and opamps, etc., I put the inputs on the left and outputs
on the right.

-- Dave Tweed

2007\01\29@052934 by Jinx

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> I put the inputs on the left and outputs on the right

Circuits are mostly drawn and thought of as going left to right,
but just out of curiosity, is that just for people who write left to
right ? Do people who write right to left think about circuits
that way too ?

2007\01\29@061832 by Dave Tweed

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Jinx <EraseMEjoecolquittspam_OUTspamTakeThisOuTclear.net.nz> wrote:
> > I put the inputs on the left and outputs on the right
>
> Circuits are mostly drawn and thought of as going left to right,
> but just out of curiosity, is that just for people who write left
> to right ? Do people who write right to left think about circuits
> that way too ?

I don't know about that, but I have encountered more than one
left-handed American engineer who tended to draw circuits that
way, probably subconciously.

-- Dave Tweed

2007\01\29@073211 by olin piclist

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Jinx wrote:
> Circuits are mostly drawn and thought of as going left to right,
> but just out of curiosity, is that just for people who write left to
> right ? Do people who write right to left think about circuits
> that way too ?

yawyna sdrawkcab-ttub etirw wef yreV  .wonk t'nod I

********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2007\01\29@074009 by Jinx

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> > Do people who write right to left think about circuits that way too ?
>
> yawyna sdrawkcab-ttub etirw wef yreV  .wonk t'nod I

? elpmaxe rof srekeaps cibarA

2007\01\29@080053 by Rolf

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Jinx wrote:
>>> Do people who write right to left think about circuits that way too ?
>>>      
>> yawyna sdrawkcab-ttub etirw wef yreV  .wonk t'nod I
>>    
>
> ? elpmaxe rof srekeaps cibarA
>
>  
w b t t I
e o o h
l t p e T
l t   y h
 o t   o
 m o w u
     r g
 a   o h
 s   t t
     e



2007\01\29@091814 by Gerhard Fiedler

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David VanHorn wrote:

> Maybe some day, we'll get the ability to insert links into schematics and
> source code. Click here on the schematic to see the data sheet, click
> there to see the definition of the pins on port B or the chip pinout in
> the source code.

While I'm still using a package that doesn't support this, I add the
datasheet URL into a custom field in the parts library. Since I export my
BOMs always into CSV files which I import into a spreadsheet (where I then
create the real BOMs), the links can become "clickable" there.

I also have a spreadsheet with the footprint areas and an estimation
factor. Adding all the (area * factor) items up for a design gives a
reasonable good estimate of the required board area even before doing any
placement.

Gerhard

2007\01\29@093442 by alan smith

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Viewdraw has that ability, when you generate a pdf of the file at least, you can link to a datasheet from the library (within viewdraw).  Inside the schematic, you can also do this as well, thru its properties.

David VanHorn <dvanhornspamspam_OUTmicrobrix.com> wrote:  

Maybe some day, we'll get the ability to insert links into schematics and
source code.
Click here on the schematic to see the data sheet, click there to see the
definition of the pins on port B or the chip pinout in the source code.
--




---------------------------------
Don't be flakey. Get Yahoo! Mail for Mobile and
always stay connected to friends.

2007\01\29@102435 by David VanHorn

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On 1/29/07, Gerhard Fiedler <@spam@listsKILLspamspamconnectionbrazil.com> wrote:
>
> David VanHorn wrote:
>
> > Maybe some day, we'll get the ability to insert links into schematics
> and
> > source code. Click here on the schematic to see the data sheet, click
> > there to see the definition of the pins on port B or the chip pinout in
> > the source code.
>
> While I'm still using a package that doesn't support this, I add the
> datasheet URL into a custom field in the parts library. Since I export my
> BOMs always into CSV files which I import into a spreadsheet (where I then
> create the real BOMs), the links can become "clickable" there.


Right, I can do this with my favorite, old dos orcad.  But what I want is to
be able to right click on a part in the schematic, and pull up the data
sheet, and probably a mathcad file (or similar) on how it's value was
selected.  For bonus points, I'd see the whole circuit set up in mathcad (or
similar) and have component values calculated on the fly.  Right click on a
resistor, and click on "change value", and all the parts affected go yellow,
then enter the new value, and the calculations are done, and new values
picked from the appropriate 5%, or 1% resistor values, and so on.

I often wonder why even the most modern tools are so primitive.

The current versions of "orcad" by cadence have pretty good BOM generation,
and are more oriented like eagle, where there are no "generic" parts, every
part is a specific part, with specific values, and footprint.
But as far as I'm aware, they still suck more than all the hoovers ever
built.

2007\01\29@120441 by gacrowell

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{Quote hidden}

> --

2007\01\29@120505 by gacrowell

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> Maybe some day, we'll get the ability to insert links into
> schematics and
> source code.
> Click here on the schematic to see the data sheet, click
> there to see the
> definition of the pins on port B or the chip pinout in the
> source code.

We do this on our library parts now, and it has completely changed the
way we do both schematic and layout design reviews.  Subject sch/pcb is
on the projector screen and component data are just a click away;
resolves issues immediately that would have been an agenda item for (yet
another) meeting.  And, of course, it's just as valuable at design time
too. Since I've created or reworked most of the library components, at
least 98% of our components now have linked datasheets, and often
footprints (if not in the datasheet) and app notes as well.  Even R's &
C's have 'sheets.  At this point, there'd be a riot if I stopped
including the links.

As I've mentioned before, we are gradually moving to Altium Designer 6,
and though we haven't explored it much, I believe that it has the
ability to embed a great variety of design information within the
schematic.

Gary Crowell, PE CID+
Micron Technology

2007\01\29@144330 by Brooke Clarke

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Hi:

The OP was about how to understand circuits and so rearranging the
schematic components to have inputs on the left and outputs on the right
is the way to go.  It's a common reverse engineering sort of thing.  But
if troubleshooting, or board layout are the focus then pin number order
has advantages.

The shop manuals for Rolls Royce cars have two electrical wiring
diagrams.  One is the functional diagram which is similar to the
schematic where the flow is left to right.  The other is the practical
diagram where every wire joint and terminal is shown.  These two
diagrams are very different, but work well together.  Of course the
place  you need to probe is always hidden behind a door pillar where
it's near impossible to access the joint.


Have Fun,

Brooke Clarke

--
w/Java http://www.PRC68.com
w/o Java www.pacificsites.com/~brooke/PRC68COM.shtml
http://www.precisionclock.com


'[EE:] How do you create and understand circuits?'
2007\02\04@171248 by peter green
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> Jinx wrote:
> > Circuits are mostly drawn and thought of as going left to right,
> > but just out of curiosity, is that just for people who write left to
> > right ? Do people who write right to left think about circuits
> > that way too ?
>
> yawyna sdrawkcab-ttub etirw wef yreV  .wonk t'nod I
i presume he was refereing to people whose native language was something like hebrew or arabic where writing from right to left is the correct way not people who write english backwards.


2007\02\04@180234 by Jinx

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> i presume he was refereing to people whose native language was
> something like hebrew or arabic where writing from right to left is
> the correct way not people who write english backwards

Yes. Although presumably the Israeli Philharmonic doesn't have
music scores that are re-written right to left for them


2007\02\04@183939 by David VanHorn

picon face
>
> We do this on our library parts now, and it has completely changed the
> way we do both schematic and layout design reviews.  Subject sch/pcb is
> on the projector screen and component data are just a click away;
> resolves issues immediately that would have been an agenda item for (yet
> another) meeting.  And, of course, it's just as valuable at design time
> too. Since I've created or reworked most of the library components, at
> least 98% of our components now have linked datasheets, and often
> footprints (if not in the datasheet) and app notes as well.  Even R's &
> C's have 'sheets.  At this point, there'd be a riot if I stopped
> including the links.


Very interesting.   I'm glad to see that SOMETHING out there is moving along
with the times!
Now if only I could get a source code editor that worked that way.

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