Circuitry Mystery


2011-04-29 8:37 pm
I've always wondered how components (capacitors, resistors, ic's, etc.) and their values
in a circuit board are determined. Seems mind boggling!:confused:

There are usually many different ways to reach the desired circuit functionality.
You consider factors like cost, size, accuracy, safety, number of units to build,
and your previous experience in the particular design area.
Sometimes, it's as simple as Ohm's law. When circuits get more complex,
computer simulation is usually required. Try reading a good introductory book. Art of Electronics - Horowitz & Hill.pdf
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2009-03-08 3:36 am
i was completely baffled by how it all works and i still am. but getting to grips with ltspice and eagle is teaching me loads and its fun. you cant blow anything up and its free. i have been playing for about 3 weeks and getting a dab hand at making schematics.

i also brows the internet looking at what components actually do and how they work such as transistors.

Mooly has some fantastic tutorials that have brought me on leaps and bounds by changing values of components in ltspice and seeing what the results bring. i then make up schematics and boards in eagle. ooohhh and did i say its fun :)

Mooly's Tutorials
but getting to grips with ltspice is teaching me loads and its fun. you cant blow anything up and its free

That's half the fun when it blows up.
If it just works you have learned nothing.
A good long session tracing voltages and checking components is good for experience and gaining understanding.

I bought a second hand Maplin amp and replaced missing components.
It didn't work, just sounded very distorted. I checked every component and they all tested ok.
After a long time I suddenly twigged some joker had replaced an npn transistor with a pnp ! The transistor number had worn off and was no help.
I never thought to check transistors for type with my mulitmeter. I just checked for shorts.

I have been in electronics/software 35 years and still continue to learn. Its an ongoing exercise for life.


2010-04-24 1:52 am
That's half the fun when it blows up.
If it just works you have learned nothing.
I wouldn't say nothing, but there's a huge amount you don't learn that way.

With Mooly's first circuit with the 3 ohm and 7 ohm resistors in series and connected to 10 volts, how warm does each resistor get? Maybe too hot to touch? Which will be the first one to start smoking and glowing like in that video? What is the actual power dissipated in each resistor (okay, LTspice can answer that one) and what would be appropriate power ratings for these resistors?

Why does a particular big resistor on a circuit board have overly bent leads and why is it a half inch above the PCB instead of being flush like all the other components?

How hot does a 5 watt resistor get when you put 5 watts of electricity into it?

LTspice (at least when used solely for schematic entry and sim, which is probably about 99 percent of its use) won't answer these questions, but doing such circuits in the Real World will give you a good idea, and enough "intuitive" experience to ask things like "is that heat sink big enough?"