# Understanding complex circuits_What to know?

#### BC547

Joined May 22, 2018
41
Hello dear Electronics hobbyists/Engineers/Scientists,

I studied mechanical engineering along with a semester containing a subject on basic electronics. 10+ years later, I still wish to build and see things working together on a breadboard. There is some satisfaction in creating something on your own! Apart from small circuits with less than 4 to 5 components (resistor, capacitor, transistor etc), I haven't had an easy time progressing the much bigger circuits. I literally freeze, wondering what's going on? Specifically, I get confused at nodes or junctions where a capacitor-resistor is connected both to the voltage and ground, and I am thinking what comes first ?
Willing to work and study on my own if there are people who had the same situation or offer suggestions.
Reading a ton of books in the past has not really solved this problem.
If you read my post, I am sincerely looking for your tip.

#### dl324

Joined Mar 30, 2015
16,732
Whatever electronics courses you took as part of your ME major were only superficial. If you want to be able to design circuits, you need to understand how each device works and be familiar with basic design practices (such as derating components, choosing parts that aren't over specified). It takes years/decades for someone with an EE degree to become proficient as a designer.

If you're confused by nodes, you need to study the basics because that's first term EE curriculum and you should have covered that in your ME classes on EE.
I haven't had an easy time progressing the much bigger circuits. I literally freeze, wondering what's going on?
Well drawn schematics will group components by function. Work on identifying the blocks and analyze the blocks individually.

For example, I designed a dual tracking voltage regulator for a member and used simple building blocks so he could understand how it worked:

There's the obvious regulator IC plus 3 other blocks. A voltage divider, and inverting amplifier, and a voltage follower. Whatever voltage the LM317 is set for will generate a negative voltage of the same magnitude.

1. Can you identify the blocks?
2. Can you understand how they work?
3. Can you determine why certain components and values were selected? Why is R1 100 ohms? Why is R2 2k? Why is there a voltage divider? Why was a 2N3906 used? Which components determine how accurate tracking will be?
4. Can you identify limitations? Minimum/maximum output voltages? Maximum input voltage? Maximum output currents?
For the sake of clarity, power supply connections for the opamp and capacitors aren't shown.

This is the thread if you're interested.

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#### BobTPH

Joined Jun 5, 2013
8,686
I get confused at nodes or junctions where a capacitor-resistor is connected both to the voltage and ground, and I am thinking what comes first ?
I have no idea what is meant by “what comes first” in ths context. Please explain.

Bob

#### KeithWalker

Joined Jul 10, 2017
3,034
The way I learned about electronics in my early teens was by building circuits that other people had designed, and by reading about how they worked. I built my first radio, a four valve (vacuum tube) TRF reflex circuit when I was 12, in 1950. I then experimented by modifying parts of the circuit until I was satisfied with the results. I read everything on circuit construction that I could get my hands on. Electronic components that I could afford with my allowance were hard to find so I wound my own power transformers, made my own capacitors, and bought junk radios and other electronics at the local second hand store. When transistors became available I learned far more about them by experimenting and destroying them than I ever learned from a book.
My advice is, if there is some kind of circuit or electronic device that intrigues you, read about it and give it a try. Use someone else's circuit. Make measurements and try to understand how it works. You will learn far more from hands-on than by studying. The big advantage nowadays is that affordable components are readily available on line by mail order.
Good luck,
Keith

#### Papabravo

Joined Feb 24, 2006
21,029
I left college with a BSEE degree in 1970. It was nearly 16 years before I designed my first board level product; it was a Z-80 single board computer. This was at a time when a CAD system was out of reach, and the schematic had to be hand drawn. I read a lot of datasheets, studied other designs, and the whole process required considerable attention to detail because board turns were on the expensive side. The board went into production with no "blue" wires on either side.

#### Ian0

Joined Aug 7, 2020
9,531
It's a lot trickier these days to solder those blue wires on!

#### Wolframore

Joined Jan 21, 2019
2,609
and no longer blue, i use transformer wires and SMD's stack nicely.

#### Papabravo

Joined Feb 24, 2006
21,029
It's a lot trickier these days to solder those blue wires on!
Takes a cool head and a keen eye. Engineers may not have the right skill set, that's why we appreciated the NASA trained technicians.

#### Dodgydave

Joined Jun 22, 2012
11,255
Reading electronic magazines ETI, Elektor, Practical Electronics,,or circuit diagrams is the best way to understand more, how each component works , like op amps, transistors, fets, putting them together and building your own circuit on Veroboard or breadboard is invaluable , .

https://www.epemag3.com/projects.html

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#### Ian0

Joined Aug 7, 2020
9,531
I learned my electronics from the magazines, ETI was my favourite. There doesn't seem to be so many around these days, but all the old ones are on line - All the basics are really well explained in magazines from the 70's and 80's - probably because basics is all there was in those days.
and all the other issues are there as well
When you have mastered ETI, move on to Wireless World.

#### dl324

Joined Mar 30, 2015
16,732
When I worked at HP in the late 70's, they allowed up to 10 wires to be added to a board before it had to be rejected. This was to correct PCB manufacturing defects, not design defects, in HP3000 Series III computers.

#### KeithWalker

Joined Jul 10, 2017
3,034
When I worked at HP in the late 70's, they allowed up to 10 wires to be added to a board before it had to be rejected. This was to correct PCB manufacturing defects, not design defects, in HP3000 Series III computers.
I remember seeing them! I worked in Test and Measurement from 71 until 2003.

#### dl324

Joined Mar 30, 2015
16,732
Speaking of well drawn schematics (or the lack thereof), here's something I came across drawn by an EE professor or TA:

Which is much easier to understand if it's drawn like this:

#### KeithWalker

Joined Jul 10, 2017
3,034
dl324, I agree. Circuit diagrams are much easier to understand if conventions and signal flow are observed when laying out a circuit diagram. I have a difficult time following simple circuits that are drawn in the modern style like complex systems, with fragmented pieces all over the page, connected only by their labels. I think that part of the problem comes from people using software tools to to do their thinking for them
I believe in "keep it simple".
Keith

#### dl324

Joined Mar 30, 2015
16,732
I think that part of the problem comes from people using software tools to to do their thinking for them
Schematic editors don't place components, so the ignorance is between the ears of the author.

What I find most distressing about that schematic is that it was drawn by/for an institution of higher learning.

Tweaked schematic:

The LM319 symbol is wrong. They show the inputs to be pins 2 and 3 and show connections the comparator doesn't have. If pin 7 is the output, the inputs are pins 9 and 10.

#### Wolframore

Joined Jan 21, 2019
2,609
Looks like they meant to use the LM211/311. Another peeve is they probably just used the same diagram for the 741 and just relabled things on it.

#### Wolframore

Joined Jan 21, 2019
2,609
It's an interesting lab creating PWM which can then be demodulated, too bad about the typos. It would be better if they used a higher modulation frequency so it can be filtered out easier. We made a similar one in class once but used an opamp as a comparator.

#### dl324

Joined Mar 30, 2015
16,732
We made a similar one in class once but used an opamp as a comparator.
The Maxim schematic used 2 opamps as comparators. That's understandable since they were using a quad opamp.