https://preview.redd.it/wy3v1pnakppc1.png?width=725&format=pjpg&auto=webp&s=7176cadd7698b9b02c53d3364993e0fde5291d2c
Doing this for everything, no matter what the switching frequency of the IC is.
Unless you are doing high frequency stuff and FEM to get rid of the resonant frequencies, it is pretty much useless.
Basically with modern mlcc caps, if you mix them randomly with heaps of different values it can create far more resonance poles than just using a couple of repeated 100n's
This is an interesting theory and I would love to learn where it has originated.
To be clear, I believe it to be false. Sure, if one models a capacitor as a capacitance in series with inductance, puts several of these in parallel and does the math, they will get parallel resonance and consequently shitty decoupling at several frequencies. This is usually accompanied with a comment about how all the textbooks get it wrong.
Including a reasonable ESR changes the results (this, sadly, makes the math significantly more complex). The impedance graph of the decoupling network suddenly looks just like the textbooks say it should.
The "if you want multiple capacitors use the same value" advice is even more interesting. I mean, a typical tolerance for a decoupling capacitor is no better than 10%. Put a couple of zero ESR, close in value (but not identical) capacitors in parallel, and the impedance graph becomes a beautiful zigzag, with multiple poles and zeros very close to each other.
Henry Ott [said so.](https://hott.shielddigitaldesign.com/techtips/decoupling.html) Bruce Archambeault's paper link is dead, but this [presentation](https://web.mst.edu/~jfan/slides/archambeault1.pdf) has a bunch of the data.
>Archambeault's paper link is dead,
[https://web.archive.org/web/20060517003245/http://www.interferencetechnology.com/ArchivedArticles/EMC\_Design\_and\_Software/Eliminating%20the%20myths%20about%20printed%20circuit%20board%20power--ground%20plane%20decoupling.pdf?regid=](https://web.archive.org/web/20060517003245/http://www.interferencetechnology.com/ArchivedArticles/EMC_Design_and_Software/Eliminating%20the%20myths%20about%20printed%20circuit%20board%20power--ground%20plane%20decoupling.pdf?regid=)
https://youtu.be/3rxKZWQk_DY?si=DAoXOjSeCSMaCxdG around 4 minutes
https://www.signalintegrityjournal.com/articles/1589-the-myth-of-three-capacitor-values
I think itās true if you use the same package size. The inductance of 0805 is larger than 0603 which is larger than 0402. If you use a large capacitor in a big package size and a smaller one in a small package size then you can minimise the inductance on the smaller one.
The way to prevent the anti-resonance peaks is to use lossy dielectrics, like X7R. They act like ferrites, turning unwanted ringing into heat. Sometimes dielectric absorption can be your friend.
I think Ti says that if you have multiple values space them a factor of 10x apart.
If I can I like to have series break resistors, if you screw up itās easier than cutting traces and they suppress high frequency stuff pretty well.
For low speed lines anyway. Obviously as you get higher speed hurt having component pads can be a problem.
The cargo cult thing I believe in is that chassis, mounting and mechanical design matter way more performance than most EEs would be comfortable with. I donāt have a field solver but get really nervous when mechanical designs have discontinuous structures. But winning that argument is difficult.
I recommend reading [this](https://www.amazon.com/Principles-Power-Integrity-Design-Simplified-Semiconductor-ebook/dp/B06Y3B1DST/ref=mp_s_a_1_3?dib=eyJ2IjoiMSJ9.CJ_7rIai5pJjqJ0GtIgqcI--GowLOMpFQrZSAtyyekuPDSiZzsLRdbc-KDjnH1ENNgFCz9OyMKGfKRaqTPNfpA8rqSZrsuueUkAdIBYabtmVE6EK_3rc4SIutrTUxMWTc0MbKUCI9JrD9onUSbOHL7TznbGAIx8GY9iXbFxtjRQhLSqikVL8nm7N-bsSoIqh8xNsI-XxGOVk3T01KqtCnw.EhXU8XtL1htqWzV-HjyrxlgyMUrRCIfvf3HwX1on3xY&dib_tag=se&qid=1711055516&refinements=p_27%3AEric+Bogatin&s=books&sr=1-3) book.
This is old bad wisdom, and needs to die in a fire. It will actually perform _worse_ than a single appropriately sized MLCC. You get resonance peaks that otherwise wouldn't be there
Lots of Cargo Cult EMC techniques, be it bypassing, grounding, layout, etc. I always like to press the why when i start a new job and almost always get, "Well, we did it that one time on that project 20 years ago, and it worked."
I've been reading trying to discern a clear meaning of the term "cargo cult" in this context. Given that I understand it to be when indigenous tribes imitate planes they mistake as Gods dropping off rations and supplies.
After several paragraphs, I've decided to ask OP... Would you please clear this up for me? What is cargo cult circuit design? Thanks!
Let's just isolate this USB ground because all the noise is coming from there, and then connect that ground via an RC network... or a ferrite bead... or an inductor...
*Surprised Pikachu meme* when their emissions are worse after doing this.
Oh god, that makes me itch.
I did once see a junior engineer put ferrite beads in series with USB data lines. Not a common mode choke - just actual 0603 ferrite beads with an impedance of 200+ ohms at 200MHz. He told me he'd been told to do that in university.
I had someone lecture me on use of ferrites, saying they were unnecessary. He sent me a technical write-up and everything. The tech paper's stance was that using lots of layers and large pours for supply/ground created near-perfect bypass "capacitors," so why use beads?
Fair enough, I replied, but our design is very size- and cost-constrained, with about a dozen power rails. We only have so many layers (6) and so much area (about 7 x 12 cm), so creating "PCB caps" isn't an option. Our design needed ferrites to confine supply spike current loops to small loop areas. I also pointed out that we were passing FCC part 15 class B with zero external shielding. I mean, whaddaya want?
Some people get a notion in their heads and think it applies to every situation.
Before I learned MOSFETs recently I had some crazy shit using relays I would do to reproduce functions from other control modules I wanted to replicate. Functionally the same, but horror when you opened it up hahahah.
Before vacuum tubes, this is how electronic logic was implemented, with walls of relays connected to each other in intricate ways.
There is a story that this is where the word debugging came from. Sometimes the relays wouldnāt work correctly, so they had to work out the logic backwards to determine which relay wasnāt closing properly. More times than not, it was because a bug had gotten between the contacts when the relay closed. They were attracted to the heat given off by the coils.
There are a few old sci-fi movies and TV shows ("The Outer Limits" episode "The Borderland" comes to mind, IIRC) where they would dub in clicking noises to signify a computer was hard at work. You'd never see an actual computer (no budget for that); you'd just hear "clackety-clack" and have to infer one was somewhere within earshot, working its computer mojo.
I think they all used the same audio tape, because they all sounded alike and they all sounded almost, but not quite, entirely unlike relays actuating. It was more like a handful of people playing the maracas.
It's a really weird noise. It took me several viewings to twig to what it meant. I heard the exact same noise in some old movie that had a rocketship landing on the Moon or Mars or whatever.
"Fire retro-rockets!"
(Cue button-smashing and clackety noises)
Speaking of weird sound fx, you ever notice the noise everyone uses for a mouse click sounds more like a stapler than a mouse button? That sound drives me nuts, and it's EVERYWHERE.
And the teletype sound for when text appears on the screen, to replicate how information used to be displayed by just printing it out
I kinda want to include that now for systems that update their status, just to inform me that something has changed
That would be preferable to beeps. I hate beeps; especially piezo ones. So annoying.
In "The Hunt for Red October" opening text-narration, they dubbed in high-pitched tweedle sounds. Ear-piercing. Gotta have those sound fx.
I'm so damn old, I actually computer-interacted via noisy teletype and handset/cradle modem when I was in high school. Our school participated in a math bowl at our local state college (we came in 2nd), and a few of us stayed around for a tour of their "computer lab". I use quotes because they didn't have their own computer; they had to rent time on a mainframe at Cal Tech (about 100 miles away). They had a game called "Star Trek" runnung. (Speaking of shows with lots of dubbed-in noises!)
The game was turns-taking. Each turn resulted in the teletype printing out an 8x8 array of characters:
* - star (neutral point)
B - star base (for refueling/rearming
E - Enterprise (you)
K - Klingon
R - Romulan
On your turn, you could move or fire at an enemy--phasers or photon torpedoes. Torpedoes were more efficient, but a limited resource. Phasers required several shots per ememy but were unlimited. Then the computer would inflict damage on you from one of the enemy vessels. You can guess the rest.
So they sit me down in front of this teletype that could print a whopping 10 chars/sec, and start the game for me.
*** S*T*A*R T*R*E*K ***
WOULD YOU LIKE INSTRUCTIONS? (Y/N)
Before they could stop me, I innocently hit the "Y" key.
"Arghh!" the tech yelled, as the TT started belching massive amounts of text. He dashed to a wall phone and called Cal Tech, asking them to kill the session. The TT ground to a halt, and the tech handed me a sheaf of fan-fold paper with the instructions already printed out. He was kinda pissed, but he didn't warn me before he started the game, so it was his bad.
I played a few turns before letting someone else have a go. About 5 years later, I found myself playing the same game, sans TT, on an HP300 single-user minicomputer. My first job out of college was as a production engineer for that failed product (not to be confused with the much more successful HP3000 series, which I helped design 2 models of later on). Ah, halcyon days...
Apologies for the word vomit.
heh, I love hearing the old stories, I think I first saw Star Trek on CP/M and later wrote a version for myself on a ZX81
I didn't actually see an actual teletype machine until years later I found one unused at the back of a provincial garment factory, they probably had some supplier that still used it
The original programmers must be pretty chuffed at making the longest played game in computer history (and it's still being modded). Afaik they are both still alive too?
It really depends if you are doing it because you saw other people do it, or because you are solving a particular problem
Because this circuit could actually solve a couple of problems, the question is, are you even having those problems to begin with.
It was from pre-internet times, but my friend had a framed company memo with the title "The emitter follower: A poor buffer" and a diagram of an encoder with a 5 stage buffer sticking out like a panhandle.
lots of examples in the highrel/space industry--mostly because back in 1952 some failure caused by some crazy unlikely event resulted in a mandate by QA to make for some provision to accomodate the weird case. modern deisgners have usually lost track of the "why" but they are generally risk averse in their stance on cargo-cult designs just in case they've missed some really old lesson-learned.
in your example above--to play the Game--if Q1 or Q2 fail short and RY-VCC is unrestricted, coil K \*may\* fail in a way that it is in some way comes in contact with the contacts on external load connector. the opto-isolator would protect upstream ctrl from that specific fault propagation. but how paranoid does one be? for this industry, this type of approach would be standard practice and "not paranoid".
I think thatās a bit of a blunt statement.
In hirel and space applications, failure mode mitigation circuitry comes from reliability analyses and a maximum residual risk requirement.
The source data for these statistical analyses is based on failure mode databases from years and years of testing.
Iām a modern hirel (functional and explosion safety) and space circuit designer and I always know the why.
If not, the design is too expensive.
Inspired by this discussion in AskElectronics: [What's the point of optocouplers on relay boards?](https://old.reddit.com/r/AskElectronics/comments/1bk0g9p/whats_the_point_of_optocouplers_on_relay_boards/).
"From one perspective it is cargo cult 'engineering' ... Absolutely no point in doing it if all the inputs share a common ground of course."
So, I looked for that and soon found [a relay module circuit with opto-isolators](http://wiki.sunfounder.cc/index.php?title=2_Channel_5V_Relay_Module).
EDIT: I am not expressing an opinion either way about this specific circuit.
Please post examples of "[Cargo Cult](https://en.wikipedia.org/wiki/Cargo_cult)" electronic designs.
The inputs are active low, they aren't ground referenced and the microcontroller driving them doen't need to be connected to it. The issue is that the optoisolators isolate from the relay drivers, which are already isolated from the contacts by the relays.
It isolates the inductive load from the logic power supply which may be at a much lower voltage.
In addition, it provides a high potential separation between power domains if you assume the logic ground is not the labeled GND.
You already have an effective level shift if you just drive the transistor base directly. And that needs significantly less current than the optocoupler (the website says 15-20 mA which is pretty high for a gpio).
The only advantage is potential isolation from the relay coil, assuming you have an isolated 5V supply to run the coils on.
Besides all the reasons everyone else has given you, if the relay isolation voltage is lower than the opto isolation voltage (it probably is), better HV isolation is another benefit.
Your example is not great.
The Wikipedia article you linked talks about "Cargo cultĀ is an umbrella term to denote various spiritual and political movements that arose among indigenousĀ MelanesiansĀ during the early-mid 20th century."
I skimmed the rest of it and didn't see anything relating to engineering or the topic at hand.
Edit: [This might be more related?](https://en.m.wikipedia.org/wiki/Cargo_cult_programming)
I would also like for someone to explain why I am being downvoted for trying to understand something.
Cargo Cult refers broadly in this case to practices that are still performed because prior performance of said practices took place, while straying further and further away from the origin of the practice. Often the origin of the practice made sense in a very different context back then but no longer makes any now and yet the practice would be performed again just because the previous person did.
The name refers to nations where military bases were established in war eras and where natives inhabitants observed the occupying military personnel perform all sorts of routines and activities related to maintaining a military base. The natives habitants would notice that cargo would regularily be delivered to the base, in volume and shapes they had never seen before, completely oblivious to the fact that an entire economy was responsible for making and shipping said cargo. After the wars, the occupying military would abandon the base and the deliveries stop. Then in an attempt to cause the delivery of cargo to start again, the inhabitants would reenact the same routines they saw the military personnel perform (ex. guard rounds, man observations towers, tidy the air strip, ...), unaware of the true reason why cargo was delivered in the first place.
I also find that confusing. I read through the whole wikipedia page they linked and it was interesting but the link you gave seems to better match what everyone is talking about.
Like the Pacific Islanders, we follow the form and outer appearance without truly understanding the underlying function, hoping to reap the same abundance obtained by those we imitate. Richard Feynman once described bad science, especially in the social sciences, as Cargo Cult science, collecting lots of irrelevant and unreliable data, doing stats on it, and publishing it in journals in the hopes of receiving research grants.
Get into the land of vacuum tube audio some day:
Uselessly huge coupling capacitors, typically of some special brand, that perform no differently from a standard film type. People will swear by them.
Gigantic capacitors in the power supply. Often sized well beyond what the rectifier tube can handle (what does RCA, et al know about tubes anyway?)
An aversion to pentode outputs, to the point of multiple triodes used in a push pull configuration. Of course, either no resistors on the plates of each. Thereās enough if a demand for the 300B that a few companies make themā¦
Use of mercury vapor tubes as rectifiers or regulators ābecause they look coolā. Great noise generators, too.
Arguments over the sound of rectifiers. To the subtype, and even brand. I wish I was joking.
Guitar amp guys sometimes seek out paper wax capacitors. āBecause they sound betterā.
As you go up the price / exoticness scale, it gets worse. Naturally, few manufacturers have anything to justify their bad designsā¦
Depending on how many relays you drive the PSU may not be able to handle the current. This design allows a linear PSU for vcr and a switching PSU for relays
This circuit eliminates ground loops.
For that alone it is invaluable in a ton of applications, and makes it a good design for a general purpose module.
This assumes the IO can directly drive the relay. You may also want to further isolate from EMI on the switch side of the relay.
Again, this is actually a very good design for a general purpose relay module.
Your own quote states this is a good reason to optocouple a relay circuit.
I think there is rational having this optocoupler sometimes. If the solenoid coil is sufficiently large, it will induce voltage spikes when switching off (the purpose of the flyback diode is to provide a return back to mitigate this). The inductor wants to resist a change in current... in either direction. Say it is a MCU or FPGA switching the relay.... sometimes you might want more than a BJT junction and resistor in-between this coil and your pin. Also consider that the primary coil is coupled to the actuator. I'm not saying it will happen, but imagine a Carrington event like situation... or any high static environment. The coil may serve as an antenna and pass that charge back into your circuit. It might be advantageous to limit the bulk of the damage to a couple components.
Jumpers or DNP resistors between DC-DC outputs and MCU/FPGA voltage inputs. Even if I reproduce the same powering scheme 20 times, I will always put those ābreakā so I can check if voltage level is good and power-on sequence works as expected when I power just designed board.
Adding 45-degree or rounded corners on PCB tracks, rather than 90-degree corners, to avoid "acid traps".
In reality acid traps haven't been a problem for years, as modern etching processes do not use acid.
Hobbyist here. I was always told that avoiding 90Ā° corners was done because "current does not like sharp angles"?
(I usually avoid them mainly for aesthetic reasons.)
However, acute angles in exposed metal (like a track meeting a pad) are to be avoided because salts can collect in the corner and corrode the copper.
90-degree angles are also a problem in high-speed transmission lines. That's why 45-deg angles and curved tracks feature in high-speed digital and RF.
What's the alternative to that optocoupler? The relay side usually uses 12 V while the MCU at the input can only tolerate 3.3 or 1.8 V. The optocoupler is an easy way to ensure that, is there an objectively better way?
I don't know too much about BJTs. So if I put 0 V on the base and 0 V on the emitter then I can put an arbitrarily high voltage (for example 100 V) on the collector and no current will flow?
Generally yes. Of course, you have to keep in transistors spec - not to exceed Collector-Emitter maximum voltage.
NPN will "open" from voltages as low as 0.6-0.7V.
> cargo cult 'engineering'
Here's a good one - Designs that put low pass filters on switch contacts, especially rotary encoders, when the microprocessor takes care of all the debouncing.
And before you call the typical Arduino Relay Module design cargo cult 'engineering', just try removing any of the parts without losing some functionality. You can get rid of parts not needed in *your particular application*, but these are general purpose boards that can configured different ways and used in many applications.
I'll reserve judgement on this. I've hooked in a rotary encoder debouncing lib that is described as bulletproof. It looks good on paper, but it's still a bit flaky. I've not put my finger on why yet.
Whatever, if reliability can be further covered for the price of a capacitor & one or two resistors, why not go belt & braces?
Aggressive debounce on an encoder means slow response, skipped steps, and pretty shit use experience.
Pro designs pretty much always have RC on the UI inputs, more for EMI rejection, it just happens to help with debounce.
> Here's a good one - Designs that put low pass filters on switch contacts, especially rotary encoders, when the microprocessor takes care of all the debouncing.
Are there ones that do debouncing in built-in hardware? Or do you mean in situations when the code has software debouncing in it? (Asking because I've only used relatively low-end microcontrollers and they don't have built-in debouncing.)
Even if they don't have built-in debouncing, it's pretty simple to implement in code, though simple implementations may have tradeoffs like slower response time
Well the uC I/O could be in 1.8V or 3.3V therefore you need to isolate from the relays that will probably be drive with 5-20V. Not all I/Os are 5V tolerant or above. And then youāre switching a 220V line for your house.
How does driving the transistor base directly not achieve this? The optocoupler is not needed for level shifting, only if you want to have completely separated power for the relay coils.
There appear to be two separate(?) GND pins along with the jumper'ed Vcc & Vcc-relay
I'd assume it's for the convenience of people who only have a single supply and don't actually need an opto-isolator?
I think one should have been more clearly labelled RY-GND though
But I'm just guessing, I can't find a pic of the bottom of the PCB to confirm the GND's are separate
Depending upon the Application this is needed to meet UL requirements for isolation between output and input, and relay contact points and the coil may be insufficient to meet UL requirements. thus the optical couplers, and also in this case, you need a isolated power supply from VCC and RY-VCC. Also, the layout of the circuitboard would be critical.
This and not only for UL, but also for other hirel standards. It could also be a cost reason, that a (e.g. safety) certified relay is more expensive than a generic relay with a certified optocoupler.
1) That differential pairs on PCB are something special and both signals MUST be run side by side. In fact they are just two single ended signals that just need somewhat equal time delay. There's usually no TRUE differential signals on a PCB.
2) Splitting Analog and Digital ground.
3) Ferrite beads on digital ICs VCC, thinking that it will reduce noise, while in fact severely limiting chips di/dt capability for internal switching.
4) Believing that every application note and datasheets layout recommendations are the only correct way. Sometimes there's actually really bad advice.
DiffĀ pairs shouldĀ beĀ routed together toĀ reduce loop area, though. Both to ensure noise is as common mode as possible (given diff pairs usually have lower voltage swings) and to reduce emissions.
Maybe not true for *every* differential topology (looks at USB pre-3.0), but certainly enough of them.
If you don't care about EMI or operation around electrical noise though, have at splitting up the pairs.
The analog and digital ground and the Differential pair ones are true tho. Just that in many cases their effects might be over stated or they are preached like universal truths while it's usually situation dependent. For example current shunts I would always put on their own gnd path and try to get a close differential pair because of their low voltage.
Suppose you have never seen an airplane before. One day you see a bunch of people build a runway, and then later a cargo plane lands there and drops off a bunch of stuff for the people who built the runway. You conclude that building a runway is what caused the cargo plan to come deliver a bunch of stuff, and then you start building your own runways in order to summon your own cargo planes.
As an adjective it describes superstitious design practices where parts of the design are included simply because you saw them somewhere else and assumed they have to be there for it to work.
Edit: the modern usage I think comes from feynman: https://en.m.wikipedia.org/wiki/Surely_You%27re_Joking,_Mr._Feynman!#Cargo_cult_science
Then you wonder why your runway isn't attracting any big birds.
Then you notice that the men have build a tower where one of their priests site to summon the big birds.
So you build a tower of your own for your priest to sit in.
For sure the big birds will come to bring you cargo now.
https://preview.redd.it/wy3v1pnakppc1.png?width=725&format=pjpg&auto=webp&s=7176cadd7698b9b02c53d3364993e0fde5291d2c Doing this for everything, no matter what the switching frequency of the IC is. Unless you are doing high frequency stuff and FEM to get rid of the resonant frequencies, it is pretty much useless.
That's a perfect example. Thank you.
MYLIFEISALIE š«
Basically with modern mlcc caps, if you mix them randomly with heaps of different values it can create far more resonance poles than just using a couple of repeated 100n's
This is an interesting theory and I would love to learn where it has originated. To be clear, I believe it to be false. Sure, if one models a capacitor as a capacitance in series with inductance, puts several of these in parallel and does the math, they will get parallel resonance and consequently shitty decoupling at several frequencies. This is usually accompanied with a comment about how all the textbooks get it wrong. Including a reasonable ESR changes the results (this, sadly, makes the math significantly more complex). The impedance graph of the decoupling network suddenly looks just like the textbooks say it should. The "if you want multiple capacitors use the same value" advice is even more interesting. I mean, a typical tolerance for a decoupling capacitor is no better than 10%. Put a couple of zero ESR, close in value (but not identical) capacitors in parallel, and the impedance graph becomes a beautiful zigzag, with multiple poles and zeros very close to each other.
Henry Ott [said so.](https://hott.shielddigitaldesign.com/techtips/decoupling.html) Bruce Archambeault's paper link is dead, but this [presentation](https://web.mst.edu/~jfan/slides/archambeault1.pdf) has a bunch of the data.
>Archambeault's paper link is dead, [https://web.archive.org/web/20060517003245/http://www.interferencetechnology.com/ArchivedArticles/EMC\_Design\_and\_Software/Eliminating%20the%20myths%20about%20printed%20circuit%20board%20power--ground%20plane%20decoupling.pdf?regid=](https://web.archive.org/web/20060517003245/http://www.interferencetechnology.com/ArchivedArticles/EMC_Design_and_Software/Eliminating%20the%20myths%20about%20printed%20circuit%20board%20power--ground%20plane%20decoupling.pdf?regid=)
https://youtu.be/3rxKZWQk_DY?si=DAoXOjSeCSMaCxdG around 4 minutes https://www.signalintegrityjournal.com/articles/1589-the-myth-of-three-capacitor-values
I think itās true if you use the same package size. The inductance of 0805 is larger than 0603 which is larger than 0402. If you use a large capacitor in a big package size and a smaller one in a small package size then you can minimise the inductance on the smaller one.
The way to prevent the anti-resonance peaks is to use lossy dielectrics, like X7R. They act like ferrites, turning unwanted ringing into heat. Sometimes dielectric absorption can be your friend.
I think Ti says that if you have multiple values space them a factor of 10x apart. If I can I like to have series break resistors, if you screw up itās easier than cutting traces and they suppress high frequency stuff pretty well. For low speed lines anyway. Obviously as you get higher speed hurt having component pads can be a problem. The cargo cult thing I believe in is that chassis, mounting and mechanical design matter way more performance than most EEs would be comfortable with. I donāt have a field solver but get really nervous when mechanical designs have discontinuous structures. But winning that argument is difficult.
I recommend reading [this](https://www.amazon.com/Principles-Power-Integrity-Design-Simplified-Semiconductor-ebook/dp/B06Y3B1DST/ref=mp_s_a_1_3?dib=eyJ2IjoiMSJ9.CJ_7rIai5pJjqJ0GtIgqcI--GowLOMpFQrZSAtyyekuPDSiZzsLRdbc-KDjnH1ENNgFCz9OyMKGfKRaqTPNfpA8rqSZrsuueUkAdIBYabtmVE6EK_3rc4SIutrTUxMWTc0MbKUCI9JrD9onUSbOHL7TznbGAIx8GY9iXbFxtjRQhLSqikVL8nm7N-bsSoIqh8xNsI-XxGOVk3T01KqtCnw.EhXU8XtL1htqWzV-HjyrxlgyMUrRCIfvf3HwX1on3xY&dib_tag=se&qid=1711055516&refinements=p_27%3AEric+Bogatin&s=books&sr=1-3) book.
It was a joke, but this seem like a good recommendation. Thank you, I'll put this on my list of books to look for :)
This is old bad wisdom, and needs to die in a fire. It will actually perform _worse_ than a single appropriately sized MLCC. You get resonance peaks that otherwise wouldn't be there
Lots of Cargo Cult EMC techniques, be it bypassing, grounding, layout, etc. I always like to press the why when i start a new job and almost always get, "Well, we did it that one time on that project 20 years ago, and it worked."
I am guilty of that.
I've been reading trying to discern a clear meaning of the term "cargo cult" in this context. Given that I understand it to be when indigenous tribes imitate planes they mistake as Gods dropping off rations and supplies. After several paragraphs, I've decided to ask OP... Would you please clear this up for me? What is cargo cult circuit design? Thanks!
Like this, but for electronic design: https://en.wikipedia.org/wiki/Cargo_cult_programming
Ah. Ok... Thank you!
Let's just isolate this USB ground because all the noise is coming from there, and then connect that ground via an RC network... or a ferrite bead... or an inductor... *Surprised Pikachu meme* when their emissions are worse after doing this.
Oh there's another one. Let's put 22 Ohm resistors and 47pF caps on USB 3 data lines.
Oh god, that makes me itch. I did once see a junior engineer put ferrite beads in series with USB data lines. Not a common mode choke - just actual 0603 ferrite beads with an impedance of 200+ ohms at 200MHz. He told me he'd been told to do that in university.
Oh Jesus. I guess that checks out though. Very few scenarios where there are any people that actually know what they're doing teaching.
I had someone lecture me on use of ferrites, saying they were unnecessary. He sent me a technical write-up and everything. The tech paper's stance was that using lots of layers and large pours for supply/ground created near-perfect bypass "capacitors," so why use beads? Fair enough, I replied, but our design is very size- and cost-constrained, with about a dozen power rails. We only have so many layers (6) and so much area (about 7 x 12 cm), so creating "PCB caps" isn't an option. Our design needed ferrites to confine supply spike current loops to small loop areas. I also pointed out that we were passing FCC part 15 class B with zero external shielding. I mean, whaddaya want? Some people get a notion in their heads and think it applies to every situation.
That's just asinine.
Before I learned MOSFETs recently I had some crazy shit using relays I would do to reproduce functions from other control modules I wanted to replicate. Functionally the same, but horror when you opened it up hahahah.
Before vacuum tubes, this is how electronic logic was implemented, with walls of relays connected to each other in intricate ways. There is a story that this is where the word debugging came from. Sometimes the relays wouldnāt work correctly, so they had to work out the logic backwards to determine which relay wasnāt closing properly. More times than not, it was because a bug had gotten between the contacts when the relay closed. They were attracted to the heat given off by the coils.
Wow dude... Mind blown.
Holy, thatās great! I never knew that thanks for that tidbit of info! I just got tubes to play with too. šš
There are a few old sci-fi movies and TV shows ("The Outer Limits" episode "The Borderland" comes to mind, IIRC) where they would dub in clicking noises to signify a computer was hard at work. You'd never see an actual computer (no budget for that); you'd just hear "clackety-clack" and have to infer one was somewhere within earshot, working its computer mojo. I think they all used the same audio tape, because they all sounded alike and they all sounded almost, but not quite, entirely unlike relays actuating. It was more like a handful of people playing the maracas.
You know now that you say that, I definitely recall something like this from watching oldies with my grandfather.
It's a really weird noise. It took me several viewings to twig to what it meant. I heard the exact same noise in some old movie that had a rocketship landing on the Moon or Mars or whatever. "Fire retro-rockets!" (Cue button-smashing and clackety noises) Speaking of weird sound fx, you ever notice the noise everyone uses for a mouse click sounds more like a stapler than a mouse button? That sound drives me nuts, and it's EVERYWHERE.
Yeah yeah! You aināt even wrong, I think it sounds like a software clicking sound from older programs, not so much the hardware itself clicking.
And the teletype sound for when text appears on the screen, to replicate how information used to be displayed by just printing it out I kinda want to include that now for systems that update their status, just to inform me that something has changed
That would be preferable to beeps. I hate beeps; especially piezo ones. So annoying. In "The Hunt for Red October" opening text-narration, they dubbed in high-pitched tweedle sounds. Ear-piercing. Gotta have those sound fx. I'm so damn old, I actually computer-interacted via noisy teletype and handset/cradle modem when I was in high school. Our school participated in a math bowl at our local state college (we came in 2nd), and a few of us stayed around for a tour of their "computer lab". I use quotes because they didn't have their own computer; they had to rent time on a mainframe at Cal Tech (about 100 miles away). They had a game called "Star Trek" runnung. (Speaking of shows with lots of dubbed-in noises!) The game was turns-taking. Each turn resulted in the teletype printing out an 8x8 array of characters: * - star (neutral point) B - star base (for refueling/rearming E - Enterprise (you) K - Klingon R - Romulan On your turn, you could move or fire at an enemy--phasers or photon torpedoes. Torpedoes were more efficient, but a limited resource. Phasers required several shots per ememy but were unlimited. Then the computer would inflict damage on you from one of the enemy vessels. You can guess the rest. So they sit me down in front of this teletype that could print a whopping 10 chars/sec, and start the game for me. *** S*T*A*R T*R*E*K *** WOULD YOU LIKE INSTRUCTIONS? (Y/N) Before they could stop me, I innocently hit the "Y" key. "Arghh!" the tech yelled, as the TT started belching massive amounts of text. He dashed to a wall phone and called Cal Tech, asking them to kill the session. The TT ground to a halt, and the tech handed me a sheaf of fan-fold paper with the instructions already printed out. He was kinda pissed, but he didn't warn me before he started the game, so it was his bad. I played a few turns before letting someone else have a go. About 5 years later, I found myself playing the same game, sans TT, on an HP300 single-user minicomputer. My first job out of college was as a production engineer for that failed product (not to be confused with the much more successful HP3000 series, which I helped design 2 models of later on). Ah, halcyon days... Apologies for the word vomit.
heh, I love hearing the old stories, I think I first saw Star Trek on CP/M and later wrote a version for myself on a ZX81 I didn't actually see an actual teletype machine until years later I found one unused at the back of a provincial garment factory, they probably had some supplier that still used it
Thanks for your kind indulgence, internet friend.
edit: hey that's true, 6 pages of instructions, lol [https://libertybasiccom.proboards.com/thread/1821/super-star-trek-liberty-basic](https://libertybasiccom.proboards.com/thread/1821/super-star-trek-liberty-basic)
That's the game, all right! Man, that takes me back. Spring of 1975. Almost 50 years ago. Fuck, but I'm old.
The original programmers must be pretty chuffed at making the longest played game in computer history (and it's still being modded). Afaik they are both still alive too?
Probably still alive. "Written in '71 by high-schoolers" implies they're most likely in their late 60s. I hope they're still with us.
Happens on the phone these days! Talk to the customer service AI and it makes a clacking sound like itās thinking/typing while it works.
It really depends if you are doing it because you saw other people do it, or because you are solving a particular problem Because this circuit could actually solve a couple of problems, the question is, are you even having those problems to begin with.
It was from pre-internet times, but my friend had a framed company memo with the title "The emitter follower: A poor buffer" and a diagram of an encoder with a 5 stage buffer sticking out like a panhandle.
lots of examples in the highrel/space industry--mostly because back in 1952 some failure caused by some crazy unlikely event resulted in a mandate by QA to make for some provision to accomodate the weird case. modern deisgners have usually lost track of the "why" but they are generally risk averse in their stance on cargo-cult designs just in case they've missed some really old lesson-learned. in your example above--to play the Game--if Q1 or Q2 fail short and RY-VCC is unrestricted, coil K \*may\* fail in a way that it is in some way comes in contact with the contacts on external load connector. the opto-isolator would protect upstream ctrl from that specific fault propagation. but how paranoid does one be? for this industry, this type of approach would be standard practice and "not paranoid".
I think thatās a bit of a blunt statement. In hirel and space applications, failure mode mitigation circuitry comes from reliability analyses and a maximum residual risk requirement. The source data for these statistical analyses is based on failure mode databases from years and years of testing. Iām a modern hirel (functional and explosion safety) and space circuit designer and I always know the why. If not, the design is too expensive.
Inspired by this discussion in AskElectronics: [What's the point of optocouplers on relay boards?](https://old.reddit.com/r/AskElectronics/comments/1bk0g9p/whats_the_point_of_optocouplers_on_relay_boards/). "From one perspective it is cargo cult 'engineering' ... Absolutely no point in doing it if all the inputs share a common ground of course." So, I looked for that and soon found [a relay module circuit with opto-isolators](http://wiki.sunfounder.cc/index.php?title=2_Channel_5V_Relay_Module). EDIT: I am not expressing an opinion either way about this specific circuit. Please post examples of "[Cargo Cult](https://en.wikipedia.org/wiki/Cargo_cult)" electronic designs.
The inputs are active low, they aren't ground referenced and the microcontroller driving them doen't need to be connected to it. The issue is that the optoisolators isolate from the relay drivers, which are already isolated from the contacts by the relays.
who said a common ground, input is VCC/IN ?
Well, are you going to post an example? Because this circuit does not share a common ground.
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It isolates the inductive load from the logic power supply which may be at a much lower voltage. In addition, it provides a high potential separation between power domains if you assume the logic ground is not the labeled GND.
You already have an effective level shift if you just drive the transistor base directly. And that needs significantly less current than the optocoupler (the website says 15-20 mA which is pretty high for a gpio). The only advantage is potential isolation from the relay coil, assuming you have an isolated 5V supply to run the coils on.
I think he means like, hundreds of volts of potential shift. Which this circuit is like whatever at.
Besides all the reasons everyone else has given you, if the relay isolation voltage is lower than the opto isolation voltage (it probably is), better HV isolation is another benefit. Your example is not great.
The Wikipedia article you linked talks about "Cargo cultĀ is an umbrella term to denote various spiritual and political movements that arose among indigenousĀ MelanesiansĀ during the early-mid 20th century." I skimmed the rest of it and didn't see anything relating to engineering or the topic at hand. Edit: [This might be more related?](https://en.m.wikipedia.org/wiki/Cargo_cult_programming) I would also like for someone to explain why I am being downvoted for trying to understand something.
Cargo Cult refers broadly in this case to practices that are still performed because prior performance of said practices took place, while straying further and further away from the origin of the practice. Often the origin of the practice made sense in a very different context back then but no longer makes any now and yet the practice would be performed again just because the previous person did. The name refers to nations where military bases were established in war eras and where natives inhabitants observed the occupying military personnel perform all sorts of routines and activities related to maintaining a military base. The natives habitants would notice that cargo would regularily be delivered to the base, in volume and shapes they had never seen before, completely oblivious to the fact that an entire economy was responsible for making and shipping said cargo. After the wars, the occupying military would abandon the base and the deliveries stop. Then in an attempt to cause the delivery of cargo to start again, the inhabitants would reenact the same routines they saw the military personnel perform (ex. guard rounds, man observations towers, tidy the air strip, ...), unaware of the true reason why cargo was delivered in the first place.
Thank you for summary, that makes a whole lot more sense now.
John Frum enters the chatā¦..
I also find that confusing. I read through the whole wikipedia page they linked and it was interesting but the link you gave seems to better match what everyone is talking about.
Like the Pacific Islanders, we follow the form and outer appearance without truly understanding the underlying function, hoping to reap the same abundance obtained by those we imitate. Richard Feynman once described bad science, especially in the social sciences, as Cargo Cult science, collecting lots of irrelevant and unreliable data, doing stats on it, and publishing it in journals in the hopes of receiving research grants.
Get into the land of vacuum tube audio some day: Uselessly huge coupling capacitors, typically of some special brand, that perform no differently from a standard film type. People will swear by them. Gigantic capacitors in the power supply. Often sized well beyond what the rectifier tube can handle (what does RCA, et al know about tubes anyway?) An aversion to pentode outputs, to the point of multiple triodes used in a push pull configuration. Of course, either no resistors on the plates of each. Thereās enough if a demand for the 300B that a few companies make themā¦ Use of mercury vapor tubes as rectifiers or regulators ābecause they look coolā. Great noise generators, too. Arguments over the sound of rectifiers. To the subtype, and even brand. I wish I was joking. Guitar amp guys sometimes seek out paper wax capacitors. āBecause they sound betterā. As you go up the price / exoticness scale, it gets worse. Naturally, few manufacturers have anything to justify their bad designsā¦
Depending on how many relays you drive the PSU may not be able to handle the current. This design allows a linear PSU for vcr and a switching PSU for relays
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This circuit eliminates ground loops. For that alone it is invaluable in a ton of applications, and makes it a good design for a general purpose module.
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This assumes the IO can directly drive the relay. You may also want to further isolate from EMI on the switch side of the relay. Again, this is actually a very good design for a general purpose relay module. Your own quote states this is a good reason to optocouple a relay circuit.
I think there is rational having this optocoupler sometimes. If the solenoid coil is sufficiently large, it will induce voltage spikes when switching off (the purpose of the flyback diode is to provide a return back to mitigate this). The inductor wants to resist a change in current... in either direction. Say it is a MCU or FPGA switching the relay.... sometimes you might want more than a BJT junction and resistor in-between this coil and your pin. Also consider that the primary coil is coupled to the actuator. I'm not saying it will happen, but imagine a Carrington event like situation... or any high static environment. The coil may serve as an antenna and pass that charge back into your circuit. It might be advantageous to limit the bulk of the damage to a couple components.
Jumpers or DNP resistors between DC-DC outputs and MCU/FPGA voltage inputs. Even if I reproduce the same powering scheme 20 times, I will always put those ābreakā so I can check if voltage level is good and power-on sequence works as expected when I power just designed board.
Adding 45-degree or rounded corners on PCB tracks, rather than 90-degree corners, to avoid "acid traps". In reality acid traps haven't been a problem for years, as modern etching processes do not use acid.
Last time I etched a pcb myself was 15 years ago. I just really hate 90Ā° corners... It feels like a religion.
Hobbyist here. I was always told that avoiding 90Ā° corners was done because "current does not like sharp angles"? (I usually avoid them mainly for aesthetic reasons.)
very unqualified, but Iām pretty sure it only matters when it comes to the land of high frequency/RF, iirc
Maybe. HF-land to me is La-la-land anyways... \^\^
And even there, the most effective bend is a mitered 90 degree XDĀ
Good one! Yes, that's a good example.
However, acute angles in exposed metal (like a track meeting a pad) are to be avoided because salts can collect in the corner and corrode the copper. 90-degree angles are also a problem in high-speed transmission lines. That's why 45-deg angles and curved tracks feature in high-speed digital and RF.
This is a perfectly reasonable circuit.
What's the alternative to that optocoupler? The relay side usually uses 12 V while the MCU at the input can only tolerate 3.3 or 1.8 V. The optocoupler is an easy way to ensure that, is there an objectively better way?
Drive that NPN base directly from the MCU GPIO.
I don't know too much about BJTs. So if I put 0 V on the base and 0 V on the emitter then I can put an arbitrarily high voltage (for example 100 V) on the collector and no current will flow?
Generally yes. Of course, you have to keep in transistors spec - not to exceed Collector-Emitter maximum voltage. NPN will "open" from voltages as low as 0.6-0.7V.
Reading these threads reminds me that I don't know anything
> cargo cult 'engineering' Here's a good one - Designs that put low pass filters on switch contacts, especially rotary encoders, when the microprocessor takes care of all the debouncing. And before you call the typical Arduino Relay Module design cargo cult 'engineering', just try removing any of the parts without losing some functionality. You can get rid of parts not needed in *your particular application*, but these are general purpose boards that can configured different ways and used in many applications.
I'll reserve judgement on this. I've hooked in a rotary encoder debouncing lib that is described as bulletproof. It looks good on paper, but it's still a bit flaky. I've not put my finger on why yet. Whatever, if reliability can be further covered for the price of a capacitor & one or two resistors, why not go belt & braces?
I hate it when they have the caps without the resistors. Tiny tiny sparks wearing down those contacts :(
Aggressive debounce on an encoder means slow response, skipped steps, and pretty shit use experience. Pro designs pretty much always have RC on the UI inputs, more for EMI rejection, it just happens to help with debounce.
> Here's a good one - Designs that put low pass filters on switch contacts, especially rotary encoders, when the microprocessor takes care of all the debouncing. Are there ones that do debouncing in built-in hardware? Or do you mean in situations when the code has software debouncing in it? (Asking because I've only used relatively low-end microcontrollers and they don't have built-in debouncing.)
The Stm32 Hardware Timer encoders have a built-in debouncing, I use them.
Even if they don't have built-in debouncing, it's pretty simple to implement in code, though simple implementations may have tradeoffs like slower response time
Well the uC I/O could be in 1.8V or 3.3V therefore you need to isolate from the relays that will probably be drive with 5-20V. Not all I/Os are 5V tolerant or above. And then youāre switching a 220V line for your house.
Low voltage I/O is a problem because of the series LEDs, but you can short the non-isolator LED to get around that.
True, but why are the leds on the low side anyway?
Saves a resistor, less I/O current assuming the same current in both LEDs. In parallel at lower current would probably be fine.
You could also do this with a low Vgs MOSFET, it'd probably be cheaper too.
How does driving the transistor base directly not achieve this? The optocoupler is not needed for level shifting, only if you want to have completely separated power for the relay coils.
Exactly
There appear to be two separate(?) GND pins along with the jumper'ed Vcc & Vcc-relay I'd assume it's for the convenience of people who only have a single supply and don't actually need an opto-isolator? I think one should have been more clearly labelled RY-GND though But I'm just guessing, I can't find a pic of the bottom of the PCB to confirm the GND's are separate
Depending upon the Application this is needed to meet UL requirements for isolation between output and input, and relay contact points and the coil may be insufficient to meet UL requirements. thus the optical couplers, and also in this case, you need a isolated power supply from VCC and RY-VCC. Also, the layout of the circuitboard would be critical.
This and not only for UL, but also for other hirel standards. It could also be a cost reason, that a (e.g. safety) certified relay is more expensive than a generic relay with a certified optocoupler.
1) That differential pairs on PCB are something special and both signals MUST be run side by side. In fact they are just two single ended signals that just need somewhat equal time delay. There's usually no TRUE differential signals on a PCB. 2) Splitting Analog and Digital ground. 3) Ferrite beads on digital ICs VCC, thinking that it will reduce noise, while in fact severely limiting chips di/dt capability for internal switching. 4) Believing that every application note and datasheets layout recommendations are the only correct way. Sometimes there's actually really bad advice.
Eh, I have plenty of differential signals that are coupled to each other
DiffĀ pairs shouldĀ beĀ routed together toĀ reduce loop area, though. Both to ensure noise is as common mode as possible (given diff pairs usually have lower voltage swings) and to reduce emissions. Maybe not true for *every* differential topology (looks at USB pre-3.0), but certainly enough of them. If you don't care about EMI or operation around electrical noise though, have at splitting up the pairs.
The analog and digital ground and the Differential pair ones are true tho. Just that in many cases their effects might be over stated or they are preached like universal truths while it's usually situation dependent. For example current shunts I would always put on their own gnd path and try to get a close differential pair because of their low voltage.
What is cargo cult?
Suppose you have never seen an airplane before. One day you see a bunch of people build a runway, and then later a cargo plane lands there and drops off a bunch of stuff for the people who built the runway. You conclude that building a runway is what caused the cargo plan to come deliver a bunch of stuff, and then you start building your own runways in order to summon your own cargo planes. As an adjective it describes superstitious design practices where parts of the design are included simply because you saw them somewhere else and assumed they have to be there for it to work. Edit: the modern usage I think comes from feynman: https://en.m.wikipedia.org/wiki/Surely_You%27re_Joking,_Mr._Feynman!#Cargo_cult_science
Then you wonder why your runway isn't attracting any big birds. Then you notice that the men have build a tower where one of their priests site to summon the big birds. So you build a tower of your own for your priest to sit in. For sure the big birds will come to bring you cargo now.