Trying to understand how to design circuits

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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 =BFHow 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.

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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

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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

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|  James E.Thompson, P.E.                           |    mens     |
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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).

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. Add 6. Divide by 3.4. Press equal button and read answer. 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:

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:

"chriswilliams" wrote in message news: snipped-for-privacy@g47g2000cwa.googlegroups.com...

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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 suits the task best.

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.=20

NT

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Hello Chris,

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.

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

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Hello Jim,

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.

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

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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

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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 "bread board" which contains rows of spring loaded connection holes at .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.

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Keep on dreaming You must still be using Intels 8086 CPUs . I advice you to change .

Hacking teaches a guy to design a major electronics project? Wrong answer. 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.

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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 finally made.

Graham

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As if !

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

Graham

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When I was a kid I DID have a lot of "hack around" time in my dad's radio and tv repair shop.

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

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|  James E.Thompson, P.E.                           |    mens     |
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...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
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And who the f*ck might YOU be? I've never seen a contribution by you on the newsgroup... NEVER!

It's a good book "by example".

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

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
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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 snipped-for-privacy@anasoft.co.uk

SuperSpice, a very affordable Mixed-Mode Windows Simulator with Schematic Capture, Waveform Display, FFT's and Filter Design.

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^^^^^^ SHEEEESH! Another juvenile..........|

PLONK!

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
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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.