Electrical Engineering

Anindo Ghosh

01:26

@Kortuk No, I will still be traveling then, so no time unfortunately.

Kortuk

02:03

@AnindoGhosh I meant I could sunday, I think. We will see. THanks for dropping by, had missed you.

The Photon

04:32

@ScottSeidman Looks like a goof in the datasheet to me.

Luckily its symmetric so if you guess wrong about how they goofed, it's only your silkscreen that's wrong.

Rick_2047

04:51

hey all

The Photon

@Rick_2047 he

hey

Rick_2047

so what is everyone upto?

The Photon

Trying to decide if I should spend part of my weekend on a programming project for work.

Rick_2047

tough call

can you talk about the project?

The Photon

@Rick_2047 The part I might do this weekend is to write a fast convolution function. Because the library we're using doesn't allow for re-using the same filter array multiple times.

Rick_2047

05:06

MATLAB?

or C?

The Photon

C#

Rick_2047

hmm...

The Photon

Obviously not ideal for numerical stuff, but we're currently doing naive convolution so just about anything would be an improvement.

Rick_2047

but a filter array is just an array right? so how come your library prohibits you from reusing a variable?

The Photon

To do fast convolution, you take the DFT of the array. The library would re-do this step every time. My thought is I can make it faster by precomputing the DFT of the filter array.

Rick_2047

05:09

that seems obvious

wonder why the people who made the library did not do it that way

The Photon

Just trying to be more general...give it two arrays it computes the convolution. Doesn't know you used one of them before.

They also do a bunch of checks for short and long arrays, etc., and choose a best algorithm.

Since I know I'll be using roughly same size arrays each time, I can just code the one algorithm I need.

Rick_2047

so you are going to precompute the DFT and multiply the sequences?

The Photon

@Rick_2047 That's basically it...some subtleties because I have a "short" FIR filter (30-60 non-zero taps) and a "long" signal to be filtered (10,000 samples?).

32,000 samples now; might need to scale to 8e6.

"overlap-save" or "overlap-add" seem to be the basic algorithms...Wikipedia has articles on both.

Rick_2047

05:24

@ThePhoton yeah, I have studied both overlap save and add

The Photon

@Rick_2047 Somehow I managed to take some heavy-duty grad classes on signal processing (don't ask me about Hilbert spaces...) without ever taking a class on the basics.

Rick_2047

yeah, it can happen

its all about abstraction i gues

jippie

06:33

good morning @all

jippie

08:14

In my makefile, I set the CPU clock of my microcontroller by setting F_CPU.

Does this code in my .cpp file make sense (it apparently compiles, but is there a smarter way to do it) for compiling specific code?

#ifdef F_CPU
#if ( F_CPU == 1000000 ) | ( F_CPU == 8000000/8 )
// 1MHz
FUSES = { .low = LFUSE_DEFAULT , .high = HFUSE_DEFAULT , .extended = EFUSE_DEFAULT , };
#endif
#if ( F_CPU == 2000000 ) | ( F_CPU == 8000000/4 )
// 2MHz
FUSES = { .low = 0x61 , .high = HFUSE_DEFAULT , .extended = EFUSE_DEFAULT , };
#endif
#if ( F_CPU == 8000000 ) | ( F_CPU == 8000000/1 )
// 8MHz
FUSES = { .low = 0xe2 , .high = HFUSE_DEFAULT , .extended = EFUSE_DEFAULT , };
#endif
#if ( F_CPU == 16000000 ) | ( F_CPU == 16000000/1 )

jippie

08:47

I changed the #endif followed by a #if into an #elif

good mornign @abdullahkahraman

abdullah kahraman

@jippie Morning!

@jippie I have no idea

jippie

@abdullahkahraman why not?

abdullah kahraman

@jippie I am an analog guy

jippie

@abdullahkahraman Can you design a sharp 52'ish Hz LPF for me with a flat phase characteristic?

abdullah kahraman

@jippie Easy, how many OP-AMPs do you have?

jippie

08:52

OP-whats?

PeterJ

lol

jippie

@abdullahkahraman I've written opamps on my wish list for next time I'm ordering parts.

abdullah kahraman

@jippie Really?

@jippie You don't even have some LM324 lying around?

jippie

@abdullahkahraman yes, I just grabbed my pen and my wishlist and I wrote down "opamps"

I think I have a CA3130 lying around

abdullah kahraman

@jippie I assume you have already completed your "bucket list" then :)

jippie

08:55

with a date code '9006', so it is 23yrs old

abdullah kahraman

@jippie Wow! That is the same age as me, I mean literally. I was born in June '90

PeterJ

BTW, the code you have above looks generally OK @jippie, but I can't see the point to the second OR term that will always equate to the same in each case. Not that it will make a difference to compiled code so you might find it clearer.

jippie

@abdullahkahraman this is week 6 1990

abdullah kahraman

@jippie You are right, I did a selective perception

jippie

@PeterJ In my makefile I actually assign F_CPU to be '8000000/8". I thought it was being replaced with a string

@PeterJ I've learned a lot of C (and preprocessor) stuff this week :)

PeterJ

08:59

@jippie, mmmm let me think, but I thought the pre-processor always expanded expressions so it should be the same.

jippie

@PeterJ wait I can easily test that

abdullah kahraman

@jippie Why do you need a sharp 52 Hz LPF?

jippie

@PeterJ You are right, I don't get an error message :)

Have to go out, do some shopping. With the easter weekend the supermarket will be empty in a couple of hours.

PeterJ

Bye, hope you get all those choccy eggs before they are all gone

jippie

@abdullahkahraman Still the zero crossing detector, mains frequency timing little project.

@PeterJ thnx for your help :)

abdullah kahraman

09:03

@jippie Yeah, I can guess :) But why?

jippie

to suppress noise

(and there is a lot)

(even after a transformer)

(you can see modulated stuff on the scope)

out shopping. When I return I'm going to set up the TI Stellaris toolchain.

abdullah kahraman

Can you guys believe this? digikey.com/product-detail/en/MKL05Z32VFK4/MKL05Z32VFK4-ND/…

@jippie ti.com/tool/filterpro

PeterJ

09:22

Getting cheaper all the time. Has a 32-bit timer as well for anyone interested in such things ;)

abdullah kahraman

09:36

@PeterJ lol

jippie

@abdullahkahraman "Windows XP SP3 and Microsoft .NET Framework 3.5 "

@PeterJ I need a 32 bit timer!

PeterJ

I thought someone might need one so I put the wink at the end, might be worth checking out for yor project.

jippie

@PeterJ I have a TI Stellaris LaunchPad lying here, it has 32-bit timers too.

@PeterJ Does freescale have toolchain for linux anyway?

/me is out

PeterJ

09:54

Not sure, I've normally used Windows for embedded development apart from when I've wanted to target an embedded Linux system, in which case it's very useful to keep the systems the same.

abdullah kahraman

11:07

@jippie lol

@jippie I guess so, Eclipse works on Linux, right? freescale.com/webapp/sps/site/prod_summary.jsp?code=CW-MCU10

Garrett Fogerlie

@abdullahkahraman Eclipse works perfectly in linux!

jippie

11:33

@abdullahkahraman but does the compiler itself? Eclipse is just a shell around it.

abdullah kahraman

12:42

@jippie I have no idea..

Scott Seidman

13:00

@thephoton Thanks! Though so, but you're right, no real risk of being wrong.

jippie

pfff compiling the Stellaris stuff takes forever, even on my quad core machne

ManishEarth

13:27

? never had much of a problem with Stellaris (Launchpad, right?). Then again, I've just played around with it, my friend was the one actually using it

jippie

13:46

whoohoooo I flashed a binary :)

I have a green blinking LED

@Manishearth Not too much of a problem, but I compiled everything from sources and had to configure udev

Manishearth

ah

abdullah kahraman

@jippie It is the best feeling..

jippie

no the best feeling is when I write my own program from scratch and manage to get it running on the Stellaris

I only flashed an existing binary ...

oh wait the blog goes on ..

jippie

14:02

and compiled a first source :)

cool ... now I only have to figure out the hardware and the stellarisware calls ...

abdullah kahraman

@jippie Is this a 32-bit micro?

jippie

32 bit ARM

with floating point

and 32 bit timers

@abdullahkahraman perfect for my little project ... once I get the hang of the hardware and the built in ROM routines

abdullah kahraman

@jippie indeed, perfect. what is a ROM routine?

jippie

@abdullahkahraman ti.com/general/docs/gencontent.tsp?contentId=61479

abdullah kahraman

@jippie Oh, they are the libraries?

jippie

14:13

yups

abdullah kahraman

New KiCad version is out!

2013.03.19-BZR4004

I hate it!

Why they didn't create a "Release Notes" page?!

jippie

@abdullahkahraman you don't even know yet what changed and you already hate it?

abdullah kahraman

@jippie I hate that they don't show what changed!

@jippie Do you think I should overwrite the existing installation or make a fresh install?

jippie

14:39

@abdullahkahraman Are you talking Linux or Windows?

abdullah kahraman

@jippie Windows

jippie

or this apple thing

@abdullahkahraman I don't know the first thing about Windows.

abdullah kahraman

@jippie What are you using to draw schematics and PCBs?

jippie

@abdullahkahraman pencil and paper.

The Photon

@jippie You do realize sharp roll-off and flat phase response are contradictory requirements?

abdullah kahraman

14:40

@jippie How come you are an engineer?

jippie

Never needed an actual PCB yet. I only do 'one of' stuff. Once it works it's done

abdullah kahraman

@jippie Ah, man

jippie

@ThePhoton that is why I asked the question ;o)

@abdullahkahraman am I an engineer?

cool! :)

abdullah kahraman

@jippie What do you do for living?

jippie

@abdullahkahraman I'm a UNIX, networking ans security specialist

The Photon

14:41

@jippie OK, wasn't sure who was being snowed in that conversation...

abdullah kahraman

@jippie ~~Screw you, then~~ Oh, really?

@jippie Joke aside, here in Turkey, you would be treated as an experienced EE..

jippie

@ThePhoton But I am aware that some filters are flatter than others. Just can't remember the topology names that go with it.

bessel, butterworth, there was this russian guy chaykovsky or so ..

abdullah kahraman

@jippie lol

jippie

chebbychev

whatever, I'm too lazy to google for it right now.

abdullah kahraman

@jippie You do not want any gain, right?

jippie

14:45

define gain

I have a near +/-10V amplitude and I eventually need to clip it to 5V/0V

The Photon

Bessel (or Bessel-Thompson) is maximally flat phase response.

Butterworth is maximally flat passband, IIRC.

Chebychev has ripple in the passband but faster roll-off (again IIRC)

abdullah kahraman

The Photon

@abdullahkahraman now plot group delay

abdullah kahraman

@ThePhoton I don't even know what group delay is

The Photon

@abdullahkahraman It means how does the signal delay through the filter depend on the frequency,,,unequal group delay causes some funny distortions if you have wideband signals.

abdullah kahraman

14:52

jippie

@ThePhoton I guess phase stability is the most important aspect of the two

@abdullahkahraman So because I can make an LED flash using a 32 bit state of the art microcontroller, I'm an experienced EE?

abdullah kahraman

@jippie Not just that.. Look at the answers you have on EE.SE.. Those make you a good engineer here in Turkey.

For example, in this case, @ThePhoton is a guru :)

jippie

For my little project, the most important thing is that the zero crossings don't jitter due to the filter.

@abdullahkahraman I call it common sense and a bit spielerei

@ThePhoton @abdullahkahraman I guess I have to download the TI filter tool and try it from wine.

abdullah kahraman

@jippie I've heard that wine had covered a big distance.

The Photon

@jippie Or dig in to Octave or Scilab

jippie

15:18

@ThePhoton @abdullahkahraman wine doesn't like it.

I'm going to find something to eat.

W5VO

16:05

Good morning everyone

The Photon

Morning @W5VO

W5VO

So where is the hangout info?

The Photon

I'm here, hanging out.

ManishEarth

I'm here

W5VO

Where is that @kortuk?

ManishEarth

16:12

@@MORTUK IS HERE!

Kortuk

Sorry

I am back

Bringing it up, unless someone already did

Mortuk

What's being discussed today?

Kortuk

the lightning knocked out my router, been trying to get things working for a bit now

2 days ago, by Kortuk

I am leaving the google hangout on Saturday pretty open. Discuss projects, site policies or just shooting the breeze is fine, I am pretty relaxed. Just kick back and discuss everything from vacuum nanotubes to beer.

Hangout link

3

@ManishEarth @W5VO @ThePhoton @anyone else, there is the link.

Mortuk

ill have to install the plugin

Kortuk

@Mortuk Does it need a plug in?

Mortuk

16:16

Chrome on Ubuntu -- yep

Kortuk

@Mortuk haha. kk

I have to find a USB cable

brb

Mortuk

Same one as the Google voice+video chat I think. (This is a clean install of Ubuntu, I need to install lots of things)

Kortuk

ahh

kk

The more I look at raspberry pis the more I want one

jrg

i'm getting one sometime next week

Mortuk

its kinda working

jrg

16:19

the pi will be interested.

Kortuk

someone just disappeared.

jippie

I just had some apple pi

Kortuk

@jippie gonna join us?

Mortuk

@Kortuk me, I think. It keeps disconnecting me

jippie

where?

don't have a link

Kortuk

16:20

5 mins ago, by Kortuk

Hangout link

you are also invited @jrg

Mortuk

Kortuk

get it working @mortuk

The Photon

@Kortuk Clicked the link and it said I should "join Google+ by creating my public profile". :<

jrg

@Kortuk i would, but i'm doing some work. :(

Mortuk

I'm trying :P

jrg

16:21

chat.se is mind numbing enough that i don't have to worry about it.

Kortuk

@ThePhoton hmm, I am not sure, I think it might want something to show your picture.

@ThePhoton I dunno, I clearly have a G+ account, but I dont really use it for anything but this, and being able to follow occasional SE people

almost all SE people have an account

Mortuk

@Kortuk can you hear me anytime when I'm in?

Kortuk

not at all

@W5VO is now, I can hear him

I can invite you with G+ @ManishEarth and see if it helps

Mortuk

@Kortuk don't think so, similar issues happened when I tried hanging out with friends. It's a proxy thing, I guess

Kortuk

@Mortuk :(

Mortuk

16:26

strangely enough video chat does work. It's just hangouts that don't

Kortuk

@Mortuk hmm, that is odd

Mortuk

And it is the same plugin

Kortuk

@Mortuk :)

no @rick today

@rawbrawb you gonna join us?

and it goes quiet.

Mortuk

I'm here, just revising my math notes

The Photon

16:41

"It's free and installs in seconds"...Download will be completed in 1 minute...

I connected. You are now all burdened by the knowledge of my real name.

Kortuk

@ThePhoton that explains something

The Photon

Whazzat?

Who's Matthew and who's Max?

Mortuk

Max=Kortuk

I assume Matthew=W5VO

The Photon

PITA. My middle name is Max.

Text chat actually works better if you're going afk a bunch

rawbrawb

16:58

@Kortuk Wazzup?

Kortuk

@Mortuk shh. Dont tell my secrets

@rawbrawb chat session going right now

rawbrawb

@Kortuk Oh I see, you're doing a G+ hangout or something. Sorry I haven't been around much.

Mortuk

@Kortuk They're already publicly available!

Kortuk

@rawbrawb yes.

Mortuk

44 mins ago, by Kortuk

Hangout link

rawbrawb

17:00

@Kortuk next one, I gotta go right now.

Kortuk

@rawbrawb later :)

rawbrawb

Sounds like a good idea.

bye

Kortuk

18:05

Fun time guys, later.

Nick Halden

ugghhhh haha my phone is dead

and i have 2 step verification turned on

so i cant login to my google account haha -_-

Kortuk

19:09

@NickHalden haha

@ScottSeidman allo.

Rick_2047

20:04

allo

abdullah kahraman

@jippie lol

Oh, shit, I missed it!

Rick_2047

@abdullahkahraman me too

thats a bummer

abdullah kahraman

yeah

Transcript for

Electrical Engineering