Everyone knows that the path of least resistance is the path that will always be taken, be it by water, electricity or the feet of humans. This is where the PCB presented by [ElectrArc240] on YouTube is rather confusing, as it demonstrates two similarly sized traces, one of which is much shorter than the other, yet the current opts to travel via the much longer trace. If you were to measure this PCB between each path, the shorter path has the lowest resistance at 0.44 Ω while the longer path is 1.44 Ω. Did the laws of physics break down here?
Of course, this is just a trick question, as the effective resistance for an electrical circuit isn’t just about ohmic resistance. Instead the relevant phrasing here is ‘path of least impedance‘, which is excellently demonstrated here using this PCB. Note that its return path sneaks on the back side along the same path as the long path on the front. To this is added a 1 MHz high current source that demonstrates the impact of alternating current, with reactance combining with the resistance.
Although for direct current it’s fair to say that impedance is the equivalent of resistance, once the inductance of a trace has to be taken into account – as in the case of AC and high-frequency signaling – the much higher inductance of the short path means that now the long path is actually the shortest.
When you are doing some impedance matching in your favorite EDA software while implementing an Ethernet RMII link or similar, this is basically part of the process, with higher frequencies requiring ever more stringent mechanisms to keep both sides happy. At some point any stray signals from nearby traces and components become a factor, never mind the properties of the PCB material.
Electricity takes ALL paths, it’s just that some allow exponentially more electrons to flow than others. If you had sensitive enough multimeter and noise floor comparable with liquid helium, you could connect LED to a CR2032 in Japan and detect single electrons in Spain. It’s simple dynamic systems, laplace equations etc.
Perhaps it’s clear to you, but how does the electron get from Japan to Spain? What are you saying here?
Magnetics
“Nobody knows what magnetics are”
No one excepts the Spanish Inquisition
yes but is it the same electron, like is the body the same on the output on the teleport machine as it were in the input?
Didn’t you hear of the Feynman theory that all electrons are the same electron, just going backwards and forwards in time?
RE: Feynman theory about single electron – I’ve heard about it (still in the process of gradual descending down THAT rabbit hole), but I’ve also heard, say, Sean Carroll deriding it as pointless complication/confusion.
That story of electricity travels or uses the path of least resistance is never true it uses all complete paths and current divides based on their resistance
Only it’s not flowing electrons, it’s their density going forward.
Oh nose! A coil with enough henry has almost infinite resistance to HF power? Who would’ve thought HF “ELECTRICITY” doesn’t take a path of negligible resistance to DC.
I mean this if FUNCKIN HaD and nobody here as ever heard of any type of RF HF antenna… /S
Aren’t many WiFi Antennas “just” short circuits? Make a fluff video about that and get on HaD
Please – don’t put this ClickBait shit on HaD (specifically the title of that YT-vid – not sure about the content, only watched a little).
The point is not oh look inductor LOL, the point is to make people understand PCB tracks act as inductors and return path is CRUCIAL at speed. The real valuable lesson of video is at @11:00, is unintuitive and pretty much everyone gets it wrong at first (some never learn).
Easiest way to get it wrong is stitching tightly routed parallel bus to another layer by placing a bunch of VIAs close together in a neat row. Looks very aesthetically pleasing and neat. Switch PCB editor view to ground plane layer and whats that? a big cut right across it, turns out you just coupled all those tracks.
Beginners like to make “ground islands” where the only way out and back into the power supply is a winding path that dodges and weaves between traces and only connects by a tiny bridge between two vias or component leads.
It passes circuit continuity and DRC but the board will act erratically. It may even start acting up on DC if the ground return is for any significant current, like a switching transistor.
Okay, let’s try again (hopefully correct formatting this time):
No it isn’t. Not confusing and no trick question, just pure 100% unadulterated CLICKBAIT (garbage).
The electricity is still taking the path of least resistance TO IT!
Oh nose! A coil with enough henry has almost infinite resistance to HF power? Who would’ve thought HF “ELECTRICITY” doesn’t take a path of negligible resistance to DC.
I mean this if FUNCKIN HaD and nobody here as ever heard of any type of RF HF antenna… /S
Aren’t many WiFi Antennas “just” short circuits? Make a fluff video about that and get on HaD
Please – don’t put this ClickBait shit on HaD (specifically the title of that YT-vid – not sure about the content, only watched a little).
“I mean this if FUNCKIN HaD and nobody here as ever heard of any type of RF HF antenna”
And surely everyone on HAD has ages of experience building circuits and designing pcbs. There are no beginners here at all! Right?
Personally I’ve never designed a PCB – especially anything with RF.
But I’ve seen plenty of PCBs with those “wiggly” traces etc. because many if not most or even all modern PCBs with any digital communication on them have those.
And I’m confident this topic was discussed aplenty on HaD.
The larger “problem” I have is this:
A) saying impedance/inductance/capacitance between traces exist doesn’t require a YT vid
B) proper HaD article about these topics exist: https://duckduckgo.com/?q=site%3Ahackaday.com+PCB+design+inductance
C) The title of the YT vid featured here is
Perfect clickbait – at least the sub-vid-text contains “Inductance”…
Yes, this time I’m that commenter… :-/
You’re still missing the point.
The value is in giving a concrete demonstration that the loop area matters. Without it, saying PCB traces have impedance is rather academic and meaningless. Just name dropping concepts isn’t teaching.
Teaching a concept is a very valid motivation. But leading with this title is… just… yuck.
Maybe I’m old (ok, I am old), but one could actually give it a sensible title that tells you what they are discussing. And using this same clickbaity title on HaD is just really wrong. At least tell us what it is about and then we can skip it, because “duh inductance” – or read it because “WTF, inductance? PCB trace geometry?”
Yeah, I’m feeding the engagement farming.
I can excuse a clickbait title if the content is valid and not trivial.
If it tricks people into learning something, that’s ok by me. The damage is that someone who already knows it gets a refresher. Hardly anything to complain about.
Here it’s not just “duh inductance”, but why the inductance. You would intuitively assume that the longer winding path has more of both reactance and resistance, except it doesn’t. If you already know the trick, you won’t be fooled by the clickbait title. The fact that it makes you do a double take reveals that you might be skipping ahead in your assumptions.
Challenging your assumptions, even if it leads you to conclude that you were right all along, is also a teaching/learning method. The proof of the pudding is in the eating.
I found it interesting, and I have designed a reasonable number of PCB’s (as a non electrical engineer, obviously).
So that means, to me at least, this isn’t click-bait.
It’s sad how many people there are on sites like this who can’t wait to tell everyone how clever they are, and how stupid everyone else is. The “Everyone is stupid. Not me though” syndrome. They don’t realise that the overwhelming impression of such comments is one of arrogance – noone is impressed by it.
HaD – please keep posts like this coming. I am certain I’m not alone in finding them interesting.
If an article is of no value to me, I move on. I don’t deride it. We all have different interests and backgrounds.
It’s still clickbait – it’s just that not all clickbait is useless slop.
Can we fine people for disobeying Kirchhoff’s laws?
First you have to figure out where they’re hiding.
Fortunately enforcement is easy, because they won’t resist. But fines won’t do anything. We have to ground them until they conduct themselves properly.
That’s purely fascist way of thinking.
First they came for the Communists
And I did not speak out
Because I was not a Communist
Then they came for the Socialists
And I did not speak out
Because I was not a Socialist
Then they came for the trade unionists
And I did not speak out
Because I was not a trade unionist
Then they came for the J**s
And I did not speak out
Because I was not a J*w
Then they came for me
And there was no one left
To speak out for me
In this house, we obey the laws of thermodynamics.
Current splits and takes all paths and in each path it’s inversely proportional to impedance. It doesn’t “choose”. With water there is a positive feedback for current as water carves out a path.
What we also see here are dynamic heating effects. Copper has a positive temperature coefficient. So when it heats up the resistance will increase. And the trace on the bottom eventually will heat up the trace on the top. So there is a negative feedback for current. The opposite of water.
There is also a positive feedback for temperature. In practice this can cause thermal runaway where this higher resistance causes more dissipation, which in turn causes higher resistance, which in turn causes more dissipation eventually burning the trace.
Absolutely nothing to do with either impedance, or reactance (capacitive reactance does not impede the flow of current)…
When the current changes, it will take the path of least inductance. When the current settles down (i.e. steady-state DC), it will take the path of least resistance. Impedance never factors into anything…with a changing current, it will take the path that least resists the change of current (i.e. least inductive). On a multi-layer board, if the return-path is in a plane, the return current will run directly underneath the main current trace on the other side of the board, when the current changes.
They are expensive, but get Howard Johnson’s books on High-Speed Signal Propagation, and High-Speed Digital Design – The Handbooks of Black Magic…he explains it very well.
Impedance is the effective resulting resistance at a particular frequency. It is the sum total of all the different factors.
The argument as presented is like the age old debate about whether cars accelerate by torque or power…
I can’t remember what this formula was called, so i can’t look up the real formula…real “blind leading the blind” moment if you’re reading this comment expecting to be enlightened. But this is what i wish this kind of article had, because i think the math is so surprising and so evocative.
So the formula describes the resistance through a wire for an AC waveform. And it is roughly R = sin(length/wavelength). That is, as you proceed by a distance of one wavelength along the wire, the wire changes from being conductive to entirely non-conductive. I’m not sure what the negative half of the waveform means, so probably that’s an artifact of me getting the wrong formula, maybe it’s sin(length/wavelength)^2 or something like that. And I think it’s more typically expressed using irrational numbers (raising to an imaginary power is the same as sin or cos). But that core mathematical idea that a wire’s conductance oscillates wildly with its length really surprised me, but explains a ton.
We don’t tend to notice it in non-RF circuits. The wavelength of a 60Hz signal is about 5000km, so unless you’re running long-distance transmission lines you’ll never notice it, you’ll never think about it. But for, say, 60MHz the wavelength is 5 meters, which means that whether a wire acts as a conductor or insulator depends on its length on a scale that we can really appreciate.