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Excellent post! Controlled impedance took me a long time to wrap my head around when starting PCB design, the moment when it finally clicked was watching this

Excellent post! Controlled impedance took me a long time to wrap my head around when starting PCB design, the moment when it finally clicked was watching this excellent AlphaPhoenix video https://www.youtube.com/watch?v=2AXv49dDQJw& https://www.youtube.com/watch?v=2AXv49dDQJw& asking and practically demonstrating the simple question: When you flip on a switch, to turn on anything, send data, morse something etc, how does the circuit know how much current the load at the other end needs? Spoiler: Given that information can't travel faster than light, the simple answer is: it doesn't. So it just guesses and adjusts, which you don't want as it gives you exactly the ringing etc Heaviside identified. The video is a nice complement, as it perfectly visualizes the issues at play. It's a pretty wild bit of understanding to have, even in simple situations like flipping on a light switch.

thijson 2y ago
I remember reading about the first cable that was laid across the Atlantic. https://en.wikipedia.org/wiki/Transatlantic_telegraph_cable https://en.wikipedia.org/wiki/Transatlantic_telegraph_cable They didn't know much about transmission line theory, and even burned out the cable at one point. Heaviside was only about 8 years old when the first cable was laid down.
deleted 2y ago
[deleted]
CharlesW 2y ago
That video (and channel, seemingly) is incredible, thank you for posting! I've never seen anything like the visualizations starting at ~10m.
nyrikki 2y ago
That video is good for the water like wave explanation that is a very useful lens. If you want a more in-depth explanation, particularly how the field is in the dielectric and the wires/traces are simply the wave guide, this long presentation by Rick Hartley will help move to the next level. https://www.youtube.com/live/ySuUZEjARPY https://www.youtube.com/live/ySuUZEjARPY The dramatic shift in behavior above the audio frequency range is where the water wave lens starts to fall down IMHO. I was looking at my brothers memory card from a Cray 1a the other day and that video popped in my head. They had the timing traces snaking through several flat-pack chips legs. No wonder they had to move from parity to Hamming code even with exclusively using differential twisted pairs between modules.
- brunohaid 2y ago
  That one‘s gold too, but for me it was the other way round - needed Hartley to fully grasp Alpha Phoenix. Understanding waves feels a bit like the bell curve meme for me: you start with the mental water model, and eventually end up with it again. Or Feynman: you hear him helpfully talk about bouncy rubber balls, then learn a bunch of stuff over the next decade, and randomly listen to the same lecture again, and suddenly all sorts of „aaaah, that’s what he meant“ lightbulbs go off.
  - nyrikki 2y ago
    I should also clarify something above, Oliver Heaviside did discover the energy flows through the dielectric, most explanations like that video use other lenses to communicate the very real need to consider voltage and current. The original link side stepped that as to be honest it is to complicated for the intended use case. All models are wrong, some are useful, and the water wave model is very useful for very real needs. I personally wasted a lot of time confusing the map for the territory, but yes everyones path will be different. I confused the "electron flow" and water wave model as being absolute ground truth for way longer than I would like to admit.
  - elteto 2y ago
    Watching the Alpha Phoenix video I had a sort of realization that waves (as phenomena in general) are basically nature’s calculator/probes. If nature doesn’t “know” what will happen there’s probably some wave involved to figure it out.
    - poorcedural 2y ago
      And bias, especially in science and politics travels as a wave through time like a pendulum. Solving these systems, with the resistance measured in human lives, can take many generations.
stephen_g 2y ago
That is a great visualisation, yes! It's probably more helpful to not use the idea of 'guessing' though - the transition from off to on is a signal with a certain frequency content and that signal is reacting to the capacitance and inductance etc. of the wires and propagating through them basically the only way it can. Once the signal has propagated through and the ringing has all been absorbed it settles on the DC condition.
TeMPOraL 2y ago
> Controlled impedance took me a long time to wrap my head around (...) When you flip on a switch, to turn on anything, send data, morse something etc, how does the circuit know how much current the load at the other end needs? This kind of thing has always been my hurdle when learning electronics. Whether through tutorials or high-school level physics, all the explanations I read tend to simplify and omit things in exactly the way as to break down when you start asking questions like this. My pet peeve are various equations that people flip around seemingly arbitrarily to calculate just the thing they need at the spot, from the two "knowns" that happen to be unknown at the same spot a moment later. Everything is obviously affecting everything else, but no one thought to mention feedback loops and how to correctly deal with them (even if by simplifying them away). Or maybe I'm just a naturally imperative thinker, and I don't feel comfortable with declarative explanations which I can't "step through" mentally to understand the underlying process. Which, in case of electronics, involves voltages propagating around the circuit at finite speeds. In programming, this hit me wrt. non-deterministic programming in Prolog. Usually explained as magic. "You can assume program will compute X, because it's structured so that if it wouldn't, it would hit this 'can never happen' statement, and because that - literally - can never happen, it magically must take the correct path". Became immediately obvious to me once I realized that the runtime is just hiding a big fat loop that takes every path for you, and the magic instruction just tells it to silently discard the current path and try another one. Overall, the moment I felt I finally understand Prolog was when I realized the runtime is doing depth-first search in the background.

thijson 2y ago

I remember reading about the first cable that was laid across the Atlantic. https://en.wikipedia.org/wiki/Transatlantic_telegraph_cable https://en.wikipedia.org/wiki/Transatlantic_telegraph_cable They didn't know much about transmission line theory, and even burned out the cable at one point. Heaviside was only about 8 years old when the first cable was laid down.

deleted 2y ago

[deleted]

CharlesW 2y ago

That video (and channel, seemingly) is incredible, thank you for posting! I've never seen anything like the visualizations starting at ~10m.

nyrikki 2y ago

That video is good for the water like wave explanation that is a very useful lens. If you want a more in-depth explanation, particularly how the field is in the dielectric and the wires/traces are simply the wave guide, this long presentation by Rick Hartley will help move to the next level. https://www.youtube.com/live/ySuUZEjARPY https://www.youtube.com/live/ySuUZEjARPY The dramatic shift in behavior above the audio frequency range is where the water wave lens starts to fall down IMHO. I was looking at my brothers memory card from a Cray 1a the other day and that video popped in my head. They had the timing traces snaking through several flat-pack chips legs. No wonder they had to move from parity to Hamming code even with exclusively using differential twisted pairs between modules.

brunohaid 2y ago
That one‘s gold too, but for me it was the other way round - needed Hartley to fully grasp Alpha Phoenix. Understanding waves feels a bit like the bell curve meme for me: you start with the mental water model, and eventually end up with it again. Or Feynman: you hear him helpfully talk about bouncy rubber balls, then learn a bunch of stuff over the next decade, and randomly listen to the same lecture again, and suddenly all sorts of „aaaah, that’s what he meant“ lightbulbs go off.
- nyrikki 2y ago
  I should also clarify something above, Oliver Heaviside did discover the energy flows through the dielectric, most explanations like that video use other lenses to communicate the very real need to consider voltage and current. The original link side stepped that as to be honest it is to complicated for the intended use case. All models are wrong, some are useful, and the water wave model is very useful for very real needs. I personally wasted a lot of time confusing the map for the territory, but yes everyones path will be different. I confused the "electron flow" and water wave model as being absolute ground truth for way longer than I would like to admit.
- elteto 2y ago
  Watching the Alpha Phoenix video I had a sort of realization that waves (as phenomena in general) are basically nature’s calculator/probes. If nature doesn’t “know” what will happen there’s probably some wave involved to figure it out.
  - poorcedural 2y ago
    And bias, especially in science and politics travels as a wave through time like a pendulum. Solving these systems, with the resistance measured in human lives, can take many generations.

stephen_g 2y ago

That is a great visualisation, yes! It's probably more helpful to not use the idea of 'guessing' though - the transition from off to on is a signal with a certain frequency content and that signal is reacting to the capacitance and inductance etc. of the wires and propagating through them basically the only way it can. Once the signal has propagated through and the ringing has all been absorbed it settles on the DC condition.

TeMPOraL 2y ago

> Controlled impedance took me a long time to wrap my head around (...) When you flip on a switch, to turn on anything, send data, morse something etc, how does the circuit know how much current the load at the other end needs? This kind of thing has always been my hurdle when learning electronics. Whether through tutorials or high-school level physics, all the explanations I read tend to simplify and omit things in exactly the way as to break down when you start asking questions like this. My pet peeve are various equations that people flip around seemingly arbitrarily to calculate just the thing they need at the spot, from the two "knowns" that happen to be unknown at the same spot a moment later. Everything is obviously affecting everything else, but no one thought to mention feedback loops and how to correctly deal with them (even if by simplifying them away). Or maybe I'm just a naturally imperative thinker, and I don't feel comfortable with declarative explanations which I can't "step through" mentally to understand the underlying process. Which, in case of electronics, involves voltages propagating around the circuit at finite speeds. In programming, this hit me wrt. non-deterministic programming in Prolog. Usually explained as magic. "You can assume program will compute X, because it's structured so that if it wouldn't, it would hit this 'can never happen' statement, and because that - literally - can never happen, it magically must take the correct path". Became immediately obvious to me once I realized that the runtime is just hiding a big fat loop that takes every path for you, and the magic instruction just tells it to silently discard the current path and try another one. Overall, the moment I felt I finally understand Prolog was when I realized the runtime is doing depth-first search in the background.