### Network

M

#### Mike

Jan 1, 1970
0
Hello,

I'm relatively new to the field of electronics, and without a doubt I feel
lost when reading a large schematic. I understand that being able to read a
schematic requires thorough understanding of electronic theory, math, etc,
but is there any type of cheat sheet or tips on where to start? Obviously,
first step is determining power and polarity, but I think you get the gist..

Mike

J

#### John Popelish

Jan 1, 1970
0
Mike said:
Hello,

I'm relatively new to the field of electronics, and without a doubt I feel
lost when reading a large schematic. I understand that being able to read a
schematic requires thorough understanding of electronic theory, math, etc,
but is there any type of cheat sheet or tips on where to start? Obviously,
first step is determining power and polarity, but I think you get the gist..

Mike

The biggest help in reading a schematic is to be able to break the
system down into smaller and smaller sections, till you have fairly
simple functions to figure out. Of course, experience with a wide
range of circuits is what makes this parsing possible. I suggest you
take a fairly complex schematic, copy it and start circling
recognizable functions with colored high lighters to see how much of
it you can recognize.

M

#### Mike

Jan 1, 1970
0
Thanks, John. I'll take that algorithmic approach

J

#### John Popelish

Jan 1, 1970
0
Thanks, John. I'll take that algorithmic approach

If you need help with a specific schematic and can post a graphic of
it somewhere and link to it or post the graphic on
alt.binaries.schematics.electronic
we can talk about it and how we would pick it apart.

J

#### Jonathan Kirwan

Jan 1, 1970
0
Thanks, John. I'll take that algorithmic approach

John's point is exactly right.

But, of course, you also need to have at least some of the building blocks in
mind to do that, too. Once you pick up a few of them, you start seeing them in
places or you start seeing them slightly modified.

One thing that really threw me off when I was _first_ struggling (I still
struggle a lot as I'm just a hobbyist on this stuff) was that the published
schematics were poorly drawn for understanding. Lots of them, instead, were
drawn for helping you figure out the wiring as you soldered or connected the
parts. Or, sometimes it seemed, they were drawn to just make it really hard to
figure them out.

A class I took on electronic drafting at Tektronix in Beaverton really drilled
in a set of very simple ideas to help me unwind the Gordian Knot of a poorly
drawn schematic (the teacher kept throwing bad ones at us and making us redraw
them sensibly.) The idea was to have electron flow run like an upside down
waterfall from the bottom of the page to the top and to have signal flow go from
left to right. (The top edge is positive, bottom edge is negative, left edge is
where signals come in, and the right edge is where signals go out.) Also, the
teacher pointed out to NOT "bus" power rails around -- he said that all those
extra wires do is to distract you from the meaning. Yes, in a physical sense
those conductors will be needed when the circuit is built. But no, they do not
help you understand the circuit -- in fact, they tend to confuse you rather than
help. (This last rule isn't always exactly right, because there are a few times
in real circuits where it is IMPORTANT to show those lines explicitly -- but
that's an exception, not a rule.)

Now, keep in mind that there was NO prerequisite for this class that students
knew anything about electronic circuits. It was a drafting class and many of
them had only a glancing idea about it. So it's not like we were experts in
anything. We weren't. But just following these rules on schematics I found
that I was *much* better able to sit down and fathom their meaning.

Here's an example of a schematic that is VERY BADLY drawn. It works just fine,
though, and the wiring in the schematic is right. (What happens is... when you
press the BUTTON for a short time, it connects RLOAD to the battery and starts
the circuit so that it will keep the battery connected to RLOAD for some
designed-in time even after you release the button.)

Now, take a look at the same circuit redrawn according to the above rules:

http://users.easystreet.com/jkirwan/TimedHoldOK.png

Exact same circuit, works the same, etc. See the difference?

Just some more thoughts to consider as you go.

Jon

M

#### Mike

Jan 1, 1970
0
Thanks, John. Perhaps I can find some threads in
alt.binaries.schematics.electronic where someone (maybe even yourself) has
pulled apart schematics.

Mike

M

#### Mike

Jan 1, 1970
0
That's a pretty clever approach to dissecting diagrams. I have been doing
computer programming for eight years, and surenly that first diagram is
analogous to "spaghetti" code!

Thanks a lot for the in-depth explanation!

Mike

J

#### John Popelish

Jan 1, 1970
0
Mike said:
Thanks, John. Perhaps I can find some threads in
alt.binaries.schematics.electronic where someone (maybe even yourself) has
pulled apart schematics.

Here is an application note that picks an opamp apart into functional
pieces to explain how the whole thing works. This is an example of
what I am suggesting you try to do with other schematics.

http://www.national.com/an/AN/AN-A.pdf

Of course, the more different functional pieces you get familiar with,
the easier this gets.

C

#### colin

Jan 1, 1970
0
Mike said:
Hello,

I'm relatively new to the field of electronics, and without a doubt I feel
lost when reading a large schematic. I understand that being able to read a
schematic requires thorough understanding of electronic theory, math, etc,
but is there any type of cheat sheet or tips on where to start? Obviously,
first step is determining power and polarity, but I think you get the gist..

Mike

Sometimes it helps to re draw the circuit for yourself. Pick out simple
bits that you know like regulator circuits, op amp circuits etc.. and re
draw them as blocks so you can see how they interconect, then try figure out
bits that are left, its not always clear what the function of various
circuit paths are for even to the experienced engineer. at first sight the
multiple feedback op amp filter for example is hard to figure out until you
look at an explanation.

Colin =^.^=

J

#### Jonathan Kirwan

Jan 1, 1970
0
Sometimes it helps to re draw the circuit for yourself.

That was my recommendation, as well, unless it's already drawn well.
Pick out simple
bits that you know like regulator circuits, op amp circuits etc.. and re
draw them as blocks so you can see how they interconect, then try figure out
bits that are left, its not always clear what the function of various
circuit paths are for even to the experienced engineer. at first sight the
multiple feedback op amp filter for example is hard to figure out until you
look at an explanation.

Yes. But I also realize there is a point in time where one knows almost nothing
at all about various subcircuit sections and cannot therefore have much idea of
which circuit a resistor or capacitor is part of, for example. What really
surprised me and worked very well for me at that point in time was simply
following the drafting rules I mentioned earlier. If I redrew a schematic that
way, I found that my meager knowledge about individual components was more
easily applied to gain an abstract idea about sections I otherwise couldn't
fathom.

For example, in this controlled current drive for an LED:

+9
|
|
---
\ / LED1
---
|
|
|
|/c Q1
+CTRL------------|
|>e
|
-CTRL--, |
| |
gnd \
/ R1
\
/
|
|
gnd

is much more amenable in my mind to figuring out what it does and how it does it
(if you don't already recognize the idiom), than is this:

,-----c e--------,
| \ ^ |
| --- Q1 |
| | |
| | |
| +CTRL |
| |
--- |
D1 / \ |
--- \
| R1 /
| \
| /
| |
| |
| -CTRL----+
| |
| 9V |
| | | |
'----------||||-----'
| |

They are equivalent. But what a difference it makes to get rid of the battery
completely, arrange for the electron flow from bottom to top, signal input from
CTRL to come from the left and the LED (which is the output resulting from the
input) on the right side, and rid the schematic of power busing lines (which
only distract the eye and contribute no understanding.)

Once I started redrawing using these simple rules, not worrying initially about
organizing into functional units (which I didn't really know that much about),
then I found that the functional groupings almost stood out by themselves. When
you undo the initial knots and unkink the schematic, suddenly the actual clumps
become much more obvious because you've removed a lot of the schematic "noise."
I would then often redraw it one more time, this time with an eye to breaking it
along "apparent function" (this is pretty easy to see, even when generally
ignorant, because there are few signal wires connecting distinct functions and
there are lots of signal wires connecting bits of a single function.)

Jon

T

#### Terry Pinnell

Jan 1, 1970
0
They are equivalent. But what a difference it makes to get rid of the battery
completely, arrange for the electron flow from bottom to top

For me, it's more intuitive to say 'current flow from top to bottom'.
Strictly technically inaccurate, perhaps, but easier to follow, if

M

#### Mike

Jan 1, 1970
0
Colin, Jon, Terry -- Thanks.

Mike

J

#### Jonathan Kirwan

Jan 1, 1970
0
For me, it's more intuitive to say 'current flow from top to bottom'.
Strictly technically inaccurate, perhaps, but easier to follow, if

Understood and that's probably a good way to say it! I was just trying to be
more "physically minded," I suppose.

Jon

Replies
4
Views
1K
Replies
32
Views
3K
Replies
2
Views
639
Replies
5
Views
675
Replies
7
Views
2K