Electrical Engineering

coding_corgi

00:18

Waaaaaaaaaaaaaaaaaaaaaaaaaaaaaah!

coding_corgi

02:28

Where did the party go? :[

anorton

03:13

It went to watch Psych and Monk...

coding_corgi

@anorton ME too

Anindo Ghosh

08:51

Anyone perceive any potential problems with this solution?

0

A: How to measure velocity of a closing door

One suggestion is to have a set of inexpensive low power lasers arranged in an arc above the upper plane of the door's rotation, pointing directly downwards. A corresponding arc of PIN photodiodes or phototransistors just below the lower plane of the door's rotation can be hooked up to GPIO pins ...

jippie

09:08

good morning @AnindoGhosh

Anindo Ghosh

@jippie Heya!

jippie

yeah I see a potential problem!

@AnindoGhosh potentially too many up votes. Let me fix that right away

:-p

Anindo Ghosh

@jippie Riiiiiiiight :-)

@jippie You're forgetting that on this site, if any post demonstrates ideas or skills beyond pure inside-the-box conventional EE thinking, it gets no love from the bully-boy cartel :-D

jippie

Why use a laser and not some wide angle LED'like illuminator? The beam will be broken by the door anyway.

let me first read the question

Anindo Ghosh

@jippie Won't provide the precision he's looking for. When you go wide-angle, the beam break won't be linear (actually radial, but linear in translation motion).

jippie

09:16

@AnindoGhosh won't matter much if the detectors are close to the door

@AnindoGhosh The only thing 'wrong' with that solution is that it will be quite a large contraption.

But I like it better than the potentiometer and rotary encoder solutions

Anindo Ghosh

@jippie I added the idea of using a narrow CFL or fluorescent instead of the lasers, as you suggested. Good idea, minor loss of precision.

jippie

and of course you don't have to put the sensors at the far end of the door, it all depends on the accuracy you want.

Anindo Ghosh

@jippie Why large? Those lasers are under an inch long, quarter inch diameter. The PIN diodes are similar, 5 mm LED shaped. Upper lot on a wooden baton or strip (for rigidity), lower lot on a PCB.

@jippie I put them at the far end to milk the last drop of precision out of them. :-)

jippie

@AnindoGhosh true, but I meant the length of the whole contraption along the whole path the door 'travels'

Anindo Ghosh

@jippie They're doing testing of a prototype, they'll have the space for the jig.

jippie

09:32

@AnindoGhosh yeah that, s wy I don't like the solutions where they attach things to the door

Anindo Ghosh

@jippie Yup, attaching to door is just a no-no.

jippie

@AnindoGhosh nice drawn image BTW

Anindo Ghosh

@jippie Thx.

jippie

Haven't seen @Rick_2047 for a while

Rick_2047

@jippie will get to you guys in a bit

jippie

09:40

good boy ;o)

Anindo Ghosh

@jippie I was working on a swivel-door reactor design for a project, and had made the CAD model just recently. It looks almost like an oven, so I reworked it for the answer.

jippie

@AnindoGhosh Yeah I figured it was (largely) an off the shelf thing

Anindo Ghosh

@jippie Off the shelf to the extent that I'd already spent an hour making the reactor housing assembly (a k a the oven) yesterday :-D

jippie

@AnindoGhosh I typed (laregely)

back in a minute

Anindo Ghosh

10:01

@jippie Here's how the reactor looks... The thick bulkhead sides and door are due to potentially massive energies inside.

@jippie The window is borosiliocate glass.

jippie

@AnindoGhosh ah, thermal shock resistant

Anindo Ghosh

@jippie Yup. Pressure resistant too.

Anindo Ghosh

12:57

@jippie, help.. Conceptual confusion because of sleep deprivation.

jippie

?

Anindo Ghosh

I'm just posting an answer with a schematic, please check whether the direction of voltage change with increase in light is correct or wrong. I confused myself very successfully. :-)

0

A: How to Use SFH235 IR Photodiode Correctly?

The simplest way to connect a photodiode (even an LED can be used in this way as a photosensor) is as below: simulate this circuit – Schematic created using CircuitLab Note that the photodiode is reverse biased through the 1 Meg resistor R1. The photocurrent generated by the diode opposes...

jippie

@AnindoGhosh what do you mean by "whether the direction of voltage change with increase in light is correct or wrong."

Anindo Ghosh

> The photocurrent generated by the diode opposes the flow of leakage current through this reverse biased diode, said opposition increasing with more light on the diode junction. The voltage at the junction point thus rises in voltage with increase in light.

jippie

The photocurrent generated by the diode opposes the flow of leakage current through this reverse biased diode: OK

said opposition increasing with more light on the diode junction: I think I know what you mean

The voltage at the junction point thus rises in voltage with increase in light: Guess so, yes.

The voltage across the diode will rise with light intensity

Anindo Ghosh

13:11

@jippie Thanks.

jippie

either that, or I don't know how a photo diode works

the diode is basically a current source, with electric current flowing from gnd to the 1M resistor

the photo current forward biases the diode

Where is this this @angelatlarge character when you need him?

@AnindoGhosh you might want to clarify that paragraph a little though ... If I have to read and analyze it several times, then how about an absolute beginner in the photodiode field?

Anindo Ghosh

@jippie I see what you mean, but any clarification I can think of, adds a paragraph or two, to my mind. If you have a suggested edit, feel free to do it.

jippie

I would recommend using an internal voltage reference instead of Vcc as reference. That way you defeat the output rail to rail issue. Of course your input still might be a bit tricky.

jippie

13:39

0

Q: Why isn't project cost, maintenance cost and company profitability important here? POSIX can help

I am a bit surprised as I read this site only to discover that the basic understanding of RTOS features and benefits is more often than not based on misconceptions and I was wondering "Why?" Common Misconceptions: Using an RTOS will add overhead. I don't need an RTOS. I have been successful...

what's this?

Anindo Ghosh

@jippie It's basically spam. It's a PR move someone trying to get those keywords indexed into search engines, and "get the word out". I've flagged as spam.

jippie

I think I have to make my zero crossing timer POSIX compliant @AnindoGhosh

But there is no website out there.

Anindo Ghosh

@jippie That's an enhancement, but lack of it doesn't break the concept of the answer. Feel free to add as a comment if you like.

jippie

POSIX is nothing special either

@AnindoGhosh feeling lazy today

I did find another useless use of gnuplot though @AnindoGhosh :o)

Anindo Ghosh

@jippie No, this isn't about a web site. It's about bringing the POSIX movement into the forefront to be seen as one of the project management methodologies.

jippie

13:48

POSIX for project management!!?

Anindo Ghosh

@jippie POSIX being referred to here is more about the methodology, than about the aspect of it we are familiar with in the OS side of things.

@jippie I don't know if you remember, in the early days of Linux, there used to be such random posts by new converts to OSS, preaching the word of the linux way, almost "redeem yourself, repent, or die!"

jippie

I believe you have to pay a fee to call your OS POSIX compliant.

oh whatever, there are more interestng things to do on my sunday afternoon

coding_corgi

14:10

Yo yo yo!

jippie

@coding_corgi how come a young electronics expert like yourself only does like 2 or 3 rep on daily average over the past 4 months?

coding_corgi

@jippie Ha ha, i don't really care about rep, i see some improvement on rep on RPi

SE is sucking life out of me

jippie

who in his right mind doesn't care about rep?!

coding_corgi

@jippie me?

@jippie are you sure you are in your right mind? ;D

Anyone here use Eclipse?

jippie

14:27

what is your zodiac sign @coding_corgi?

coding_corgi

@jippie ? Is that like Horoscope?

jippie

uhhuh

coding_corgi

@jippie Ummm March?

jippie

...

Oh whetever, just tell me the name: media.jsonline.com/images/corgi+name.jpg

coding_corgi

Sir Pickles BunnyBottom

:/

@jippie There ya go, happy?

jippie

14:37

yup

coding_corgi

@jippie shut up

now the entire chat room sees that message because you starred it! ;D

jippie

not because you tell me so

coding_corgi

@jippie sure...

anorton

@jippie now, what's yours? :)

jippie

everybody knows the name of your dog now

@anorton I don't own a dog

anorton

14:39

Pretend you do. :)

coding_corgi

@anorton Hey, waz up?!

anorton

not much...

g2g... see ya

coding_corgi

@jippie i thought you were a dog.. ;D

@anorton bye bye, start the bunnybottom thing

jippie

So tell me @coding_corgi, what is it like if even you imaginary friends refuse to play with you? :-p

5

coding_corgi

@jippie ha ha

abdullah kahraman

14:46

Hi!

coding_corgi

@abdullahkahraman hullo

@jippie i dont have a dog tho

user61389

Good morning

coding_corgi

@CamilStaps well well well.... look who it is... ;D

abdullah kahraman

@CamilStaps Woah!

user61389

I'm looking for a way to get started in SDR. Ultimately I'd want to log activity on a specific frequency (with a PIC or so). The chip-part isn't the problem, but I'm looking for resources to get the RF part. Any ideas? :)

coding_corgi

14:56

@CamilStaps @PhilFrost !

user61389

@coding_corgi I know, but he's never in chat (so pinging won't work)

coding_corgi

@CamilStaps yes he is!

user61389

@coding_corgi chat.stackexchange.com/search?q=&user=61922&room=15

coding_corgi

@CamilStaps he's been here before tho

user61389

Any chance you might confuse him with someone else? ;)

coding_corgi

15:02

@CamilStaps nope

user61389

File a bug report

coding_corgi

Jun 1 at 19:46, by Phil Frost

you should hire me, because i'm apparently good at making antennas that do not radiate.

user61389

Okay. (but still, pinging doesn't work.)

coding_corgi

15:57

@CamilStaps not my problem

NickHalden

@Kortuk / Everyone: do you think this question belongs on SO or EE.SE? It doesn't seem to be getting much attention on SO...

2

Q: FreeRTOS queues and IPC confusion

I'm struggling with my first real freeRTOS project. I am basically using an ATmega328P microcontroller and an nRF24L01+ radio as a "node". I have two of these nodes and I am using them to talk to each other. I have successfully ported freeRTOS to my microcontroller so that I can use tasks to blin...

c embedded queue avr freertos

only 37 views and 2 upvotes.... one of which was from @CamilStaps

coding_corgi

@NickHalden and me

@NickHalden so impatient

NickHalden

@coding_corgi oh you were the other upvote?

coding_corgi

@NickHalden mhm

NickHalden

Ugh it almost definitely belongs on EE.SE then...

I will flag a moderator on SO and see if they want to move it.

angelatlarge

16:27

@jippie Right here!

@coding_corgi Did TheOatmeal draw a picture of you?

jippie

@angelatlarge I found a new useless use of gnuplot ;o)

angelatlarge

@jippie Oh, yeah?

@jippie Didn't realize that qualified as "Needing @angelatlarge" :)

jippie

@angelatlarge I've been working all afternoon to get gnuplot draw an image of me :o)

angelatlarge

@jippie Oh cool! Linky/posty?

jippie

angelatlarge

16:36

@jippie Pretty soon you'll adopt gnuplot to clean the litterbox for you

@jippie Is that taking a bitmap, feeding it to gnuplot as 3d data with pm3d setting?

jippie

nooo

@angelatlarge how bad do you think of me?

gamma = 2.2
color(gray) = gray**(1./gamma)
set palette model RGB functions color(gray), color(gray), color(gray)
plot "<( ./img2coord )" using 1:2:3 with image

@angelatlarge as a matter of fact the fun thing I realized today is that you can call an external script (perl in this case) from the plot command.

angelatlarge

@jippie That is neat.

jippie

maybe that external script does some PerlMagick with a PNG though :o)

of course I could just open the image directly in Firefox or so ...

angelatlarge

@jippie But this is very close to what I said. So, ok, not pm3d, but very similar. BTW, that was what I was asking you before: how to specify particular colors for each dot/point on a scatter/dot chart.

@jippie Yes. Yes you could.

jippie

I only figured gray scale. Other color palettes just look 'artistic'

angelatlarge

16:43

@jippie Well, you can give a specific palette, like so:

set palette model RGB defined ( 0 'black', 1 'brown', 2 'red', 3 'orange', 4 'yellow', 5 'green', 6 'blue', 7 'violet', 8 'gray', 9 'gray', 10 'gray' )

Anindo Ghosh

@angelatlarge Did you get a look at the sensor array layout I was trying to describe?

jippie

actually didn't really try to figure out if I could improve the colors

angelatlarge

@AnindoGhosh Yeah, thanks. They didn't seem to be bent enough for the tropics (too flat, no?), but I am curious, did you draw that yourself or did you find the image somewhere?

jippie

yeah but i would have to pull that information from the PNG too, and I couldn't really bother

angelatlarge

@jippie Right. And again, in the end, you' be recreating the PNG which you already have :)

jippie

16:45

but in a wxt terminal!

Anindo Ghosh

@angelatlarge Myself.

angelatlarge

@AnindoGhosh Wow. Very nice! Very, very, nice! Using what?

Anindo Ghosh

@angelatlarge Here's a wireframe version with hidden edges enabled, from a slightly different viewpoint.

angelatlarge

@AnindoGhosh Showoff!

jippie

I bet gnuplot can do that too.

Anindo Ghosh

16:51

@angelatlarge Of course. :-)

angelatlarge

@jippie Yeah, if you feed it the png.

jippie

ooh

Anindo Ghosh

@angelatlarge Regarding the angle of inclination: The angle should be related to whatever latitude the sensor is placed at - but I don't recall the actual relationship. I just used 30 degrees for simplicity. Unflatten as needed.

angelatlarge

@AnindoGhosh Yeah, exactly, that's why I mentioned the tropics.

jippie

and right you are!

Anindo Ghosh

16:55

@angelatlarge For some reason I thought it was [(90 - latitude)/2] (hence maximum at equator)

@angelatlarge The companies that implement the light-follower solar panel farms, they charge some insanely huge fee for those sensor blocks - and they get away with it simply because the customer almost invariably has no clue what it is, and also has some form of subsidy from their respective government or organization.

coding_corgi

17:34

@angelatlarge i. am. going. to. kill. you. (metaphorically)

AndrejaKo

Hi guys!

user61389

Hello

AndrejaKo

I'd like to ask for a small advice, if that's OK...

user61389

Sure :) (but you don't want mine ;))

AndrejaKo

I'm trying to see if a sealed lead-acid battery I have is dead...

(don't worry, I'll take full responsibility for all explosions).

2

Anyway, if I start to charge it at 14.3 V, I get this current graph:

Sample rate is 3 samples per second...

Anyway, ti seems to charge quickly, but then also quickly loses voltage.

Under 1 kiloohm load, it drops 1 mV/s.

What I'm not sure of is: Is the battery charged at current of ~100 mA near the end o the graph?

Anindo Ghosh

17:53

@AndrejaKo Plates probably pitted. Did it get deeply discharged at some point, and lie there for a while?

AndrejaKo

Well it was in an UPS which was supposed to float-charge it.

It shouldn't have been deep discharged at all.

Also it's around 2 years old.

Anindo Ghosh

@AndrejaKo If you leave it with no load for a day, how much depletion do you see?

AndrejaKo

Well, this is the first day of testing, so I don't know.

I actually have a pair of them.

Anindo Ghosh

Check the one you have not charged. What voltage with / without load? Say around 100 mA load.

AndrejaKo

They were at 12.75 V when disconnected, so I'll check the other one tomorrow and see.

OK.

Anindo Ghosh

17:58

@AndrejaKo Also, google SLA battery reconditioning. There's a way to recover a pitted plate SLA for at least some additional life, using high voltage high frequency pulses to charge it. If the plates have only surface pitting, this method works. If the plates are eaten through, then no go.

AndrejaKo

The other one, which was disconnected is at 13 V now.

The Photon

-1

Q: Minimize error in op.amps?

How do i minimize error due to Offset voltage, Bias Current, Offset Voltage, Frequency response etc. For an µa741. I have no idea on how i can cancel or just minimize the effect of these errors. I would be very glad if someone could help me :(.

op-amp ac error

Overly broad, anyone?

AndrejaKo

I'll check that!

Anindo Ghosh

@ThePhoton Perhaps more that it'd need at least 5-6 bullet points. It's answerable for entry level student audiences.

user61389

@ThePhoton besides that, it's annoying to see Andy answering all low-Q questions

user61389

18:00

Not that they shouldn't get an answer, but it would be better to try to improve the question first, IMO.

Anindo Ghosh

@ThePhoton I was tempted to write up an answer but I have some ugly workload right now.

The Photon

@AnindoGhosh Not without knowing what circuit OP is trying to make with his op-amp. As is, it requires rewriting Walt Jung's Op-amp Cookbook.

Anindo Ghosh

@ThePhoton No, I'm saying basic level: If they say 741, they're almost definitely just starting out, reading a book, and no specific application in mind. Offset null for instance, those pins have pretty much disappeared from modern op-amps.

The Photon

@AnindoGhosh Yeah, if it was just a question about how to use the offset null, that would be an okay question, even if only for historical interest.

But that's not what we have here.

This question asks about "Offset voltage, Bias Current, Offset Voltage, Frequency response etc. "

Anindo Ghosh

@ThePhoton Offset null, bias current, frequency response, all answerable in a line or two each, finishing up with a pointer to a guide or two on the web.

The Photon

18:04

He wants two explanations about offset voltage, apparently.

Anindo Ghosh

@ThePhoton Awww you're just getting testy :-) That's obviously just an error. Never mind, if you want to flag it closed, go for it, I guess.

abdullah kahraman

@CamilStaps Relax, he is fighting for the rep. Plus, it is good that he writes bunch of answers, Google information database enlarges by that..

The Photon

@AnindoGhosh I'd rather he improved the question: "I built this circuit (diagram included) and it has a problem that is probably caused by the offset current...How can I fix it?" would be just great.

angelatlarge

@AnindoGhosh That seems to be the order of the day. First @coding_corgi threatens bloody murder.. oh, wait, that's normal.

Anindo Ghosh

@abdullahkahraman Agreed. The answer is definitely a decent effort - could be more comprehensive, but then could also be a full book :-)

abdullah kahraman

18:06

I kinda like his music, "Here comes the rain": jamesoakwood.co.uk

@AnindoGhosh hahah, exactly :)

coding_corgi

@angelatlarge it's not that normal

abdullah kahraman

I wish some guys here had blogs of their own.. Even I own one! ;)

angelatlarge

@coding_corgi :)

Anindo Ghosh

@ThePhoton That's the stage after where you open a textbook and say "Ahh, a 741. What's that? Oh, it has all these problems, how do I deal with those?" - Like I said, a stage before actual circuit design.

coding_corgi

@abdullahkahraman I don't have a blog, in fact I saw @DavidKessner's blog and I was about to vomit

@angelatlarge did you finish your app?

angelatlarge

18:07

@coding_corgi Still working on it.

abdullah kahraman

@coding_corgi And why is that? He is a guy in audio business :)

user61389

@abdullahkahraman screenshotting some other webpage (the first search result) is of little use (yes, I've seen it).

The Photon

@AnindoGhosh He just needs this:

amazon.com/dp/0138896011

coding_corgi

@abdullahkahraman Ha ha... Should he have MP3 files instead of text?

@angelatlarge what's it for?

The Photon

@abdullahkahraman I have a blog. Do you want to know about local bands and volunteer work in San Jose?

user61389

18:09

@coding_corgi That's a secret.

Anindo Ghosh

@ThePhoton Yes and no. He needs to be pointed to it, but we have enough experienced people here who could give him the ABCs in 20 lines or less, before telling him to "use the force, Userxxx" :-D

abdullah kahraman

@ThePhoton Sure, I would like to read what people I know write..

coding_corgi

@CamilStaps sure... ::roll eyes::

@ThePhoton I have never used my OP amp, I have two of them I have never touched them

abdullah kahraman

@ThePhoton That book is not much liked according to Amazon reviews :)

coding_corgi

@abdullahkahraman ha ha

The Photon

18:10

@AnindoGhosh I don't think you can go from "you need to use feedback" to anything useful in 20 lines like andy tried to do.

@abdullahkahraman But if you want to know how to design basic circuits with 741's it's fine.

abdullah kahraman

@coding_corgi Good, cuz they get baked if you touch them without proper grounding wrist wraps on your ankles..

coding_corgi

@abdullahkahraman hmmm... I feeling as if your pulling my leg... :O

AndrejaKo

@AnindoGhosh After around 10 minutes with 120 ohm load, the battery now reads 12.73 V.

The Photon

@abdullahkahraman Most of the complaints seem to be about the printing quality, with a smidgen of "the information is out of date"....

abdullah kahraman

@ThePhoton I see what they did in the book description. The word "industry standard" just turns me into a doll that they can control, so they used something like that and said "industry classic"..

coding_corgi

18:13

Ha ha! It's official everyone, @ThePhoton is oldschool! ;D

Anindo Ghosh

@AndrejaKo It's just weak, either scaling or pitting. Should do well with a couple of cycles of reconditioning. I have seen an auto repair shop that does SLA reconditioning - there might be something like that around your area too.

AndrejaKo

OK, I'll check that out. Thanks!

The Photon

@abdullahkahraman I don't recommend the book for you. Just for the guy who wants to know how to design with 1970's op-amps.

@coding_corgi Old school = best school

coding_corgi

@ThePhoton ha ha, NO

Anindo Ghosh

@ThePhoton I agree with that remark.

user61389

18:17

@ThePhoton it can hardly be worse than nowadays

coding_corgi

@AnindoGhosh well u were born in the 20th century, so you like your century's tech, ;D

abdullah kahraman

@ThePhoton Yeah, I know that. I was just telling what I thought about its marketing strategies on me :)

@PeterJ I have figured out my problem about this corgi watchdog I couldn't stop :) Check out my answer. Turns out I have to see an eye doctor.

Should I add "Next time, read the manual carefully" to my answer? :)

Anindo Ghosh

0

A: Any sequence asynchronous counter

A non-linear binary counter you request does not have to be asynchronous or synchronous. The sequence is just nonlinear. Standard logic gating is used to define the sequence. The clock is irrelevant. 2 = 0010 = state 0 3 = 0011 = " 1 5 = 0101 = " 2 8 = 1000 = " 3 13= 1101 = " 4 Repeat The 5 s...

Troll?

@Kortuk See above

The Photon

@AnindoGhosh Same guy who doesn't know the difference between a PLC and a CPLD.

Anindo Ghosh

@ThePhoton My spidey sense is tingling.

The Photon

18:28

Flagged as spam.

jippie

18:41

neh don't think it is the troll

actually I can follow the reasoning

@AnindoGhosh is that bad for a battery? It would explain why my UPS battery died after it kicked in during a thunderstorm while I was on holiday for another 3 or 4 weeks.

Anindo Ghosh

@jippie Yup. Not a nice thing to do to a lead-acid battery. However, it is almost always recoverable if it's only been tortured for a few weeks.

jippie

well it is called a UPS you know, I have little use of a UPS that lasts 10 seconds after power out

jippie

19:03

R U there @AnindoGhosh?
Regarding the [MOSFET](http://pdf.datasheetcatalog.com/datasheet/SGSThomsonMicroelectronics/mXywzvy.pdf) internal diode question: I was under the same impression as you, but if you look at page 3 of the datasheet at source-drain-diode, there are some pretty nice figure in that table, aren't there?

Why would this transistor not cope?

Anindo Ghosh

@jippie Because MOSFET body diodes are slooooow.

jippie

@AnindoGhosh I was looking at the 370ns which isn't impressive, but is that the right number? t(rr) reverse recovery time

otherwise it is unspec'd

I guess the drain voltage will pull gate voltage up through the miller capacity, which will easily pull gate voltage above 20V

Anindo Ghosh

@jippie No, it is usually determined by the intrinsic inductance (18 nH in this case), which is likely to cause the shut-down spike to be expressed across a slow ramp of conduction. if there's an arbitrarily high spike across it, and it runs across a 300 nS ramp, that's not nice.

However, the gate is what fries first.

Yes, like you said, the gate will go. The insulator layer there is really thin.

jippie

@AnindoGhosh I don't see any intrinsic inductance :-s

Anindo Ghosh

@jippie Ld + Ls

irf.com/product-info/datasheets/data/irfp250.pdf

@jippie Page 2. Halfway down the page. Also see the t_on spec.

jippie

19:13

@AnindoGhosh ST doesn't have that :-p

Anindo Ghosh

@jippie That's why I went looking for another datasheet, because the one you linked was missing key points.

Anyway, I really need to go sleep.

jippie

I picked the first one

thnx for your explaination

good night @AnindoGhosh

Anindo Ghosh

@jippie I would have too, but if a datasheet has key specs missing I look for alternative versions.

MLM

22:45

ughgggghhghgh, c++ compiling is so confusing :(

coding_corgi

22:58

Yo yo yo!

@MLM methinks you forgot a semicolon

MLM

@coding_corgi nah, it's a undefined symbol problem

the linker doesn't like something

coding_corgi

@MLM oh, = instead of a -> ?

@MLM they sometimes provide line numbers, what ide are you using

MLM

@coding_corgi Keil uVision4

actually i think it is c not c++

just messing around with my STM32F3 Discovery

coding_corgi

@MLM WTF is that?! Why don't you use netbeans, eclipse, codeblocks,

MLM

@coding_corgi have to set it up

add a bunch of g++ arm stuff

coding_corgi

23:03

@MLM well do it, it should pay off

MLM

its not that.... All of the files compile but when it starts "linking..." it gives undefined symbol errors

coding_corgi

@MLM ahhhh...

@MLM it's good to compile as you go along, that way you can track down nasty mosquitoes before they go in your ears

MLM

@coding_corgi it is an example project that I want to get running

coding_corgi

@MLM do you know pyhton?

@MLM ahh

MLM

@coding_corgi never worked with it

coding_corgi

23:13

@MLM okay...

The Photon

23:38

@MLM Are the undefined symbols variables or functions, and do you think you did define them, or are they symbols you didn't even intentionally include in your code?

Also, it would be good to know for sure if you are compiling C++ or C. It will make a difference for this kind of problem.

inkyvoyd

Hello - I'm trying to understand the concept of impedance and complex ohm's law, but I'm having a bit of trouble comprehending why we use j and how it's valid. The book I'm using (The Art of Electronics) seems to make a few assertions that it doesn't explain, or I don't get. Are there any more resources I could use to understand this topic more? I'd search up questions, but I'm really not even sure what to type in to the search bar. Thanks!

The Photon

Does the Wikipedia page make things better or worse?

Electrical impedance

Electrical impedance is the measure of the opposition that a circuit presents to the passage of a current when a voltage is applied. In quantitative terms, it is the complex ratio of the voltage to the current in an alternating current (AC) circuit. Impedance extends the concept of resistance to AC circuits, and possesses both magnitude and phase, unlike resistance, which has only magnitude. When a circuit is driven with direct current (DC), there is no distinction between impedance and resistance; the latter can be thought of as impedance with zero phase angle. It is necessary to introd...

One way to think of this, a complex number is just a way to keep track of two numbers at once (magnitude and phase of an oscillating value)/

inkyvoyd

Well, I read over it and the section about the validity of the representation, but my main question is why do we need to use complex numbers and not just two variables? From my understanding, imaginary numbers allow one to make a relationship to the real numbers, but how is that significant?

The Photon

We somehow "got lucky" that we can use the rules of complex arithmetic to do calculations with these numbers, and get answers that predict the behavior of oscillating circuits/systems.

@inkyvoyd If you used two variables you'd have to write twice as many equations...

inkyvoyd

@ThePhoton I understand that part, but what I really don't get is how j^2=-1 works out

Am I just saying I don't understand why 1+1=2?

The Photon

23:49

And they might be more complicated---you'd need things like arctangents and stuff in there, where the complex arithmetic rules keep that all "swept under the rug" until you get a final solution and want to interpret it in terms of magnitude and phase.

@inkyvoyd In a way, yes..."j^2 = -1" is more or less just the definition of j.

coding_corgi

Yo yo yo!

inkyvoyd

That is what I was afraid of. For me it seems like "1+1=2" makes more sense when applied to systems than "j^2=-1".

The Photon

@inkyvoyd Another way to look at it is, when we only "knew about" the real numbers, we had no answer to the question "what's the square root of -1?"...So we said, well, whatever that number is, let's call it "j" and see what we can do with it.

I believe that historically Mathematicians had the idea of complex numbers and believed there was no practical use for them whatsoever...they just studied them for the pure theoretical mathiness of them.

Then some physicist came a long and noticed they could be used to study oscillating systems...

Ticked off the mathematicians a lot.

inkyvoyd

So, it's like how multiplication can be used to study rectangular arrays of dots?

What really intrigues me is that in the book they always just take the real part of stuff and use that, but the imaginary part does in fact play a role in determining the real part.

It feels a lot more "hidden" than imaginary

The Photon

@inkyvoyd That doesn't sound right. In electronics, the magnitude is usually much more interesting than the real part.

inkyvoyd

23:57

Well, I mean the voltage as a function of time of a sinusoidal system is Re{Ve^(jwt)} in one of the explanations - what happens to the complex part, and why isn't it important?

The Photon

Like if you pass a signal through an amplifier, you usually want to know the magnitude of the output, and sometimes the phase. The real part or imaginary part are usually not interesting on their own.

inkyvoyd

@ThePhoton if you represented the magnitude and phase of the number as some two dimensional number (x,y), you could have the same amount of information (but not in a useful form) correct? So, the reason we would use (a,bi) would just be because it is only a single variable?

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Electrical Engineering