# Trying to understand how to design circuits

C

#### chriswilliams

Jan 1, 1970
0
Hi all:

I am trying to understand the process by which the design of circuits
is carried out.
How from the white paper begins the design of a certain circuit?

In many other areas one understands that there is a certain structure,
a certain order, a process. For example:

In the case of a writing one understands that there is a thesis, main
ideas, ideas of support, a conclusion. All this must be articulated to
achieve a certain objective. This is understandable.

In the case of a car is understood that exists the motor, the electric
system, the chassis, the panel, all they complying a certain function
and thus in many other areas as the software, Civil Engineering, etc.

But in the case of the circuits all seems very confused (at least for
the novice). One doesnt know how someone decided to put a resistor
here, there a diode, or a capacitor over there. At times seems that
certain circuits were discovered by accident. Which is the center and
which the periphery.

So the question is:
Once one has certain know-how of electronics as the funcion of the
components, the basic theory, etc
¿How to proceed from the white paper to go building a certain circuit?

How to decide where to put a resistor, a diode, a capacitor, etc?

Thanks in advance by any comment.

J

#### Jim Thompson

Jan 1, 1970
0
Hi all:

I am trying to understand the process by which the design of circuits
is carried out.
How from the white paper begins the design of a certain circuit?

In many other areas one understands that there is a certain structure,
a certain order, a process. For example:

In the case of a writing one understands that there is a thesis, main
ideas, ideas of support, a conclusion. All this must be articulated to
achieve a certain objective. This is understandable.

In the case of a car is understood that exists the motor, the electric
system, the chassis, the panel, all they complying a certain function
and thus in many other areas as the software, Civil Engineering, etc.

But in the case of the circuits all seems very confused (at least for
the novice). One doesnt know how someone decided to put a resistor
here, there a diode, or a capacitor over there. At times seems that
certain circuits were discovered by accident. Which is the center and
which the periphery.

So the question is:
Once one has certain know-how of electronics as the funcion of the
components, the basic theory, etc
¿How to proceed from the white paper to go building a certain circuit?

How to decide where to put a resistor, a diode, a capacitor, etc?

Thanks in advance by any comment.

In the old days you gained experience by tinkering and burning things
up ;-)

You can't DESIGN without experience.

Try reading Win Hill's book, "Art of Electronics", CAREFULLY, trying
to understand each section before you proceed to the next.

Maybe build some kit electronics.

...Jim Thompson

J

#### Joerg

Jan 1, 1970
0
Hello Chris,
So the question is:
Once one has certain know-how of electronics as the funcion of the
components, the basic theory, etc
¿How to proceed from the white paper to go building a certain circuit?

It's the same thing as with your car or writing examples. We take what's
called a functional requirement specification (FRS) and then design the
whole thing. The other required input specs contain important data such
as target cost, monthly production quantities, mandatory agency
approvals and so on.

How to decide where to put a resistor, a diode, a capacitor, etc?

Experience, and lots of it. Analog design with discrete parts requires
more than a decade under the belt, especially if it has to result in a
very cost efficient solution. Now I hope this didn't discourage you to
get started.

Regards, Joerg

J

#### Joerg

Jan 1, 1970
0
Hello Jim,
In the old days you gained experience by tinkering and burning things
up ;-)

Hmm, old days. I just built a uC proto circuit. Then the halogen bulb of
the desk lamp blew but I figured I'd just test it really quick, that
it'll be enough daylight for that. Clouds rolled in and it got really
dark. Flipped the red and black supply wires 'cuz it was too dark.
Bzzzzt ... poof. So maybe these are the old days.

You can't DESIGN without experience.

Fully agree. But when I was a kid I didn't agree with that. The amazing
thing was that most of the stuff I designed worked anyway, including a
kilowatt size RF amp that I used to a decade. (Chris: Please don't try
to do that).

Regards, Joerg

T

#### Tim Williams

Jan 1, 1970
0
The difference is the entire philosophy on constructing a work. Electronics
is highly scientific, and as such comes from a methodic progression of ideas
and constructions, connected together. The real art is connecting the
proper building blocks together to accomplish a given function.

Given that, there are many circuits that apply both linear and
interconnected topologies (arrangements, whatever).
http://webpages.charter.net/dawill/tmoranwms/Circuits/6N7_Guitar_Amp.gif
Here's a good example of a series of stages. On the left it begins with a
common-cathode preamplifier stage, a summing paragraph as it were. (It does
in fact accomplish summation, if you add a signal to the RCA jack as well.)
The next triode (circle) splits this signal into two identical but opposite
signals for the next stages to build on. The next stage, in the middle,
amplifies the signal further, preserving balance between the opposite
signals. The second last stage increases the current capacity of the
signal, allowing it to drive the last tube, which finally turns wiggling
guitar strings into wiggling speaker cones, after the output transformer.

It's like I asked you to do this on a calculator:
Enter 7.
Multiply by 4.
Divide by 3.4.
Every operation performs some modification of the signal as it passes each
stage. It flows through every one and is processed in full.

Now on the other hand, you might have something like this:
http://webpages.charter.net/dawill/Images/Frequency Divider.gif
I'll help you out. Each pair of transistors (in the circles) facing each
other works together: when one or the other is turned on (positive voltage
on the straight line), the collector (diagonal line) is pulled down near
emitter (diagonal arrow). Say you pull down the upper-left collector node:
the voltage is transferred through the resistors, removing voltage from the
inside upper-right transistor. If the outside upper-right transistor is off
too, then the collector node will rise near +V, which puts voltage on the
inside upper-left transistor -- which you'll recall is already on, holding
its collector near zero (ground). Thus, it holds itself in one state or the
other depending on which input was last triggered, otherwise known as a
register. But there's those other resistors that connect to the diodes,
which then connect to the bottom half register, which behaves in the same
way, and also to the two transistors at the bottom. The two bottom
transistors handle the only input.

What ends up happening is, by way of everything storing, interacting and
switching, the P1 and P2 signals alternate every other clock pulse, which is
to say the clock frequency has been divided by two.

But creating these. It's different from writing, you just jump in. (This
is my first, and last, draft of this post! Jumping into say, designing
an 8-bit computer from scratch, now that's a little more troublesome. I
mentioned you always start from simpler things. In electronics, the first
thing you learn about is the circuit, a switch and lightbulb. Then you
might add a resistor, or two, and determine what happens to the voltages
depending on the resistances. (Hint: I hope you know some algebra.) Then
you can get into nonlinear (nonohmic) components like diodes and
transistors. You determine how the diode, transistor, etc. behave, then
apply it to other things, like your resistors. If you consider how the
transitor works, you can pretty quickly come up with a very high gain
amplifier. If you're clever, you can come up with a voltage regulator too,
and all other sorts of stiff, constant-voltage circuits. If you combine
both, you get an audio power amplifier!

The real genious in electronics is coming up with original connections. One
fellow back in the 1920s had the marvellous idea of sending an amplifier's
output back to its input. Applied properly, you get negative feedback which
reduces distortion. If you apply it backwards (positive feedback), you can
get an oscillator, making radio possible.

Taken to an extreme, all of today's linear amplifiers use astounding amounts
of NFB -- a factor on the order of thousands -- to reduce distortion and
improve bandwidth, with wonderful results.

Tim

--
Deep Fryer: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

<For some reason it won't add the carat indents>
Hi all:

I am trying to understand the process by which the design of circuits
is carried out.
How from the white paper begins the design of a certain circuit?

In many other areas one understands that there is a certain structure,
a certain order, a process. For example:

In the case of a writing one understands that there is a thesis, main
ideas, ideas of support, a conclusion. All this must be articulated to
achieve a certain objective. This is understandable.

In the case of a car is understood that exists the motor, the electric
system, the chassis, the panel, all they complying a certain function
and thus in many other areas as the software, Civil Engineering, etc.

But in the case of the circuits all seems very confused (at least for
the novice). One doesnt know how someone decided to put a resistor
here, there a diode, or a capacitor over there. At times seems that
certain circuits were discovered by accident. Which is the center and
which the periphery.

So the question is:
Once one has certain know-how of electronics as the funcion of the
components, the basic theory, etc
¿How to proceed from the white paper to go building a certain circuit?

How to decide where to put a resistor, a diode, a capacitor, etc?

Thanks in advance by any comment.

J

#### John Larkin

Jan 1, 1970
0
Hi all:

I am trying to understand the process by which the design of circuits
is carried out.
How from the white paper begins the design of a certain circuit?

In many other areas one understands that there is a certain structure,
a certain order, a process. For example:

In the case of a writing one understands that there is a thesis, main
ideas, ideas of support, a conclusion. All this must be articulated to
achieve a certain objective. This is understandable.

In the case of a car is understood that exists the motor, the electric
system, the chassis, the panel, all they complying a certain function
and thus in many other areas as the software, Civil Engineering, etc.

But in the case of the circuits all seems very confused (at least for
the novice). One doesnt know how someone decided to put a resistor
here, there a diode, or a capacitor over there. At times seems that
certain circuits were discovered by accident. Which is the center and
which the periphery.

So the question is:
Once one has certain know-how of electronics as the funcion of the
components, the basic theory, etc
¿How to proceed from the white paper to go building a certain circuit?

How to decide where to put a resistor, a diode, a capacitor, etc?

Thanks in advance by any comment.

If you want to learn to write, you have to write a lot. If you want to
learn how to play tennis, play tennis a lot. Circuit design is
creation, not analysis, so there's no formula. A white paper (app
note?) can be instructive about a part, but isn't often a proper basis
for a design. If it was, nobody would need designers.

So: learn the theory, theory of the parts and theory of circuits,
networks, signals+systems, and closed-loop control. Then study some
existing designs. Then start designing stuff, simple things at first,
and make sure you understand and keep control of the quantitative
aspects; you can fiddle simple circuits, but fiddling doesn't scale.

You can't get good at tennis in a week or even a year, so don't expect
to design plasma-screen TV sets first thing.

Working for a grouchy old talented mentor wouldn't hurt a bit. Design
can be taught by osmosis.

John

P

#### Pooh Bear

Jan 1, 1970
0
chriswilliams said:
Hi all:

I am trying to understand the process by which the design of circuits
is carried out.
How from the white paper begins the design of a certain circuit?

In many other areas one understands that there is a certain structure,
a certain order, a process. For example:

In the case of a writing one understands that there is a thesis, main
ideas, ideas of support, a conclusion. All this must be articulated to
achieve a certain objective. This is understandable.

You seem to be obsessed with a theoretical analysis and a 'paper design'.
Real engineers assuredly *don't* do it this way ! Then again they probably
have former practical experience !

Without practical experience a 'paper design' from pure theory is worth no
more than a block diagram. Useful for reference but unlikely to be what is

Graham

P

#### Pooh Bear

Jan 1, 1970
0
Jim said:
Maybe build some kit electronics.

As if !

Since when did most university courses give regard to practical skills ?

Graham

K

#### Kevin Aylward

Jan 1, 1970
0
chriswilliams said:
Hi all:

I am trying to understand the process by which the design of circuits
is carried out.
How from the white paper begins the design of a certain circuit?

In many other areas one understands that there is a certain structure,
a certain order, a process. For example:

In the case of a writing one understands that there is a thesis, main
ideas, ideas of support, a conclusion. All this must be articulated
to achieve a certain objective. This is understandable.

In the case of a car is understood that exists the motor, the electric
system, the chassis, the panel, all they complying a certain function
and thus in many other areas as the software, Civil Engineering, etc.

But in the case of the circuits all seems very confused (at least for
the novice). One doesn`t know how someone decided to put a resistor
here, there a diode, or a capacitor over there. At times seems that
certain circuits were discovered by accident. Which is the center and
which the periphery.

So the question is:
Once one has certain know-how of electronics as the funcion of the
components, the basic theory, etc
¿How to proceed from the white paper to go building a certain circuit?

How to decide where to put a resistor, a diode, a capacitor, etc?

Thanks in advance by any comment.

Of the order of 99%+ of all new circuits design is based on varying
existing circuits. There is a tremendous volume of well trusted and
tried topologies that have been refined over many, years and work
extremely well. All new designs should be based on these designs.
Reinventing the wheel is the last thing to do. One of the biggest
mistakes in design to try and do the "not invented here" thing. Anything
totally new will always give you grief, so don't do it unless there is
no alternative.

The way to become a good designer is to study and thoroughly understand
why existing designs work the way the do, and why they are used in a
particular application. Only by this understanding will you understand
when you have to modify an existing design to satisfy different
requirements.

A starter...recognise that design is *always* a trade off. That is
improving one aspect can only come at the expense of another aspect. For
example, G(power, speed, accuracy) = 0. That is, it is not possible to
achieve an arbitrary high speed at arbitrary low power with arbitrary
accuracy. Learn when to compromise a spec and when to tell the boss to
stick it up his arse when he doesn't.

Kevin Aylward
[email protected]
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

M

#### [email protected]

Jan 1, 1970
0
If you want to learn to write, you have to write a lot. If you want to
learn how to play tennis, play tennis a lot. Circuit design is
creation, not analysis, so there's no formula. A white paper (app
note?) can be instructive about a part, but isn't often a proper basis
for a design. If it was, nobody would need designers.

So: learn the theory, theory of the parts and theory of circuits,
networks, signals+systems, and closed-loop control. Then study some
existing designs. Then start designing stuff, simple things at first,
and make sure you understand and keep control of the quantitative
aspects; you can fiddle simple circuits, but fiddling doesn't scale.

You can't get good at tennis in a week or even a year, so don't expect
to design plasma-screen TV sets first thing.

Working for a grouchy old talented mentor wouldn't hurt a bit. Design
can be taught by osmosis.

John

I think this is the way I see it too. A designer can learn, must learn,
all the building blocks of circuits, eg amplifiers, filters, regulators
and so on, but you cant take a spec and deduce a design logically from
that. Often what comes out is logical / predictable at a block diagram
level, but equally its often not. The reason is there are so very many
options, permutations, and a seemingly endless stream of issues with
everything. Its normal to be able to use any one of a long list of
possible topologies to do the job, a skilful designer can pick what

Working with the issues gets harder over time. In the 1920s the typical
radio was a quite simple design with large issues. Today such a design
would never be accepted by the buying public, and would contravene
numerous regulations. The expectations increase over time, as do the
legal requirements, and the quality of offering of the competition.

For commercial design, yes you need experience, but for hobbeasts I
dont think its necessary. Just get stuck in, have fun, and simulate
things in spice first to save on parts. The commercial designer needs
to maximise efficiency, reliability, parts availability, cost
efficiency, and satisfy user whims. The hobbeast does not.

And IME the less rules you follow, the more you accomplish and the more
you learn, in hobby tronics. One of my gripes is hobby books always try
to emulate commercial tronics, and the 2 are really chalk and cheese.
Hobbying gives you a much wider world to play with: you can make your
own Nernst lightbulbs, make 100,000 hour lights, use positive feedback
on amplifiers, make your own moving iron or arc speaker drivers,
control systems, burger alarms, arc furnace, welders, metal formers,
mechanical amplifiers, burglar terrorisers, whatever you like.

NT

L

#### lemonjuice

Jan 1, 1970
0
My advice on what to avoid.
1) Don't come on this NG . Most of the regulars and their pals who
have been here for years don't have a clue about what electronics is
about. Avoid them like you'd avoid an epidemic! They are far worse
then that!

2) Never ever read the Art of Electronics. Its the worst book that has
ever been written on the subject.

Cheers

N

#### Noway2

Jan 1, 1970
0
When I was in High School, I took a couple of electricity and
electronics courses. A large part of the class was wiring example
circuits out of a book and analyzing how they worked. I forget how
many times I asked the teacher the same question you are now asking,
"How do you know how to connect these components to get it to do this?"
Each time I was given the same reply, "That's the engineers job",
which was why I became an electrical engineer. Little did I know that
engineering school does not teach you to design things, which I admit
was a major disappointment at the time. What it does teach you is
about the math behind different components and also how to read new
information, digest it and then apply it to a new situation, which are
things you can do on your own.

Electronic design is part art and part science and requires an
investment of time, patience, and a willingness to learn and
experiment. There is a lot of good advice in the replies to your
question. Getting the book, the Art of Electronics is a very good
place to start. I would even recommend the Lab work book that
accompanies it. From there, you will probably want to purchase a
..100" spacings (common for ICs) and a basic power supply. Then start
by building an analyzing small circuits.

One other piece of advice, for when you have an idea of what part you
want to use, but aren't quie sure how to apply it. The part data
sheets often have typical applications that show common ways to use the
device. The datasheets are also very helpfull in determining
implmementation details such as a particular pin requires a pull up or
pull down resistor of XX Ohms. Also, the datasheets will provide a lot
of information about the electrical operation of the part, e.g. how
high is a logic high output, etc, which is necessary for understanding
what building blocks are compatible.

As a word of encouragment, my first attempt at a real production design
was a simple circuit that routed a couple of RS-232 signals and power
supply connections. Quite frankly, it was a piece of crap, crude in the
design and poor in the implementation. A couple of years later, I was
designing system boards based on DSPs, with all sorts of analog and
digital circuitry. This ability didn't happen over night for me, nor
will it for you. Just keep at it.

Lastly, I would have to say that you will undoubedtly learn a hell of a
lot more from your mistakes than from what you get right. The mistakes
will force you to analyze what went wrong, which often times is not as
simple as it seems.

J

#### Jim Thompson

Jan 1, 1970
0
You seem to be obsessed with a theoretical analysis and a 'paper design'.
Real engineers assuredly *don't* do it this way ! Then again they probably
have former practical experience !

Without practical experience a 'paper design' from pure theory is worth no
more than a block diagram. Useful for reference but unlikely to be what is

Graham

When I was a kid I DID have a lot of "hack around" time in my dad's

However I WAS obsessed with mathematical analysis of circuits, and
probably remain somewhat that way after all these years.

Take a look at my analysis of the MC1530 OpAmp. I designed that
circuit through mathematical analysis, then built a breadboard to
prove it, then integrated it... I was 23 years old at the time.

...Jim Thompson

J

#### Jim Thompson

Jan 1, 1970
0
As if !

Since when did most university courses give regard to practical skills ?

Graham

...Jim Thompson

J

#### Jim Thompson

Jan 1, 1970
0
My advice on what to avoid.
1) Don't come on this NG . Most of the regulars and their pals who
have been here for years don't have a clue about what electronics is
about. Avoid them like you'd avoid an epidemic! They are far worse
then that!

And who the **** might YOU be? I've never seen a contribution by you
on the newsgroup... NEVER!
2) Never ever read the Art of Electronics. Its the worst book that has
ever been written on the subject.

Cheers

It's a good book "by example".

To learn "design" takes hacking around on your own.

...Jim Thompson

M

#### martin griffith

Jan 1, 1970
0
And who the **** might YOU be? I've never seen a contribution by you
on the newsgroup... NEVER!
Hook, Line and Sinker.......

Merry Whatever's

martin

L

#### lemonjuice

Jan 1, 1970
0
And who the **** might YOU be? I've never seen a contribution by you
on the newsgroup... NEVER!
Keep on dreaming
You must still be using Intels 8086 CPUs . I advice you to change .
It's a good book "by example".

To learn "design" takes hacking around on your own.
Hacking teaches a guy to design a major electronics project?
Don't ever look at it.
There is a poster here who claims to be the author ... Hill ...he is a
fake. Look at the quality of his replies ... absolutely useless stuff.

J

#### Jim Thompson

Jan 1, 1970
0
Keep on dreaming
You must still be using Intels 8086 CPUs . I advice you to change .
^^^^^^
SHEEEESH! Another juvenile..........|
Hacking teaches a guy to design a major electronics project?
Don't ever look at it.
There is a poster here who claims to be the author ... Hill ...he is a
fake. Look at the quality of his replies ... absolutely useless stuff.

PLONK!

...Jim Thompson

F

#### Fred Bloggs

Jan 1, 1970
0
Tim said:
Now on the other hand, you might have something like this:
http://webpages.charter.net/dawill/Images/Frequency Divider.gif
I'll help you out. Each pair of transistors (in the circles) facing each
other works together: when one or the other is turned on (positive voltage
on the straight line), the collector (diagonal line) is pulled down near
emitter (diagonal arrow). Say you pull down the upper-left collector node:
the voltage is transferred through the resistors, removing voltage from the
inside upper-right transistor. If the outside upper-right transistor is off
too, then the collector node will rise near +V, which puts voltage on the
inside upper-left transistor -- which you'll recall is already on, holding
its collector near zero (ground). Thus, it holds itself in one state or the
other depending on which input was last triggered, otherwise known as a
register. But there's those other resistors that connect to the diodes,
which then connect to the bottom half register, which behaves in the same
way, and also to the two transistors at the bottom. The two bottom
transistors handle the only input.

What ends up happening is, by way of everything storing, interacting and
switching, the P1 and P2 signals alternate every other clock pulse, which is
to say the clock frequency has been divided by two.

Could you have picked a more complicated example? No one in their right
mind would look at that archaic thing as an elemental building block
from a circuits point of view. You might have explained its
decomposition into more fundamental component circuits.

J

#### John Larkin

Jan 1, 1970
0
Of the order of 99%+ of all new circuits design is based on varying
existing circuits. There is a tremendous volume of well trusted and
tried topologies that have been refined over many, years and work
extremely well. All new designs should be based on these designs.
Reinventing the wheel is the last thing to do. One of the biggest
mistakes in design to try and do the "not invented here" thing. Anything
totally new will always give you grief, so don't do it unless there is
no alternative.

That's not design, that's copying. It's not fun, and it's usually not
very profitable, because if you can do it, everybody else can, too.

The way to become a good designer is to study and thoroughly understand
why existing designs work the way the do, and why they are used in a
particular application. Only by this understanding will you understand
when you have to modify an existing design to satisfy different
requirements.

A starter...recognise that design is *always* a trade off. That is
improving one aspect can only come at the expense of another aspect. For
example, G(power, speed, accuracy) = 0. That is, it is not possible to
achieve an arbitrary high speed at arbitrary low power with arbitrary
accuracy. Learn when to compromise a spec and when to tell the boss to
stick it up his arse when he doesn't.

John

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