Electrical Engineering

jippie

06:48

morning

abdullah kahraman

07:18

@jippie morning

jippie

@abdullahkahraman was a nice blog article I saw the other day. How did you design the CRC-filter?

abdullah kahraman

@jippie I stole it.

@jippie Btw, what CRC-filter ?

jippie

near the OPAMP, a T filter

you have the url handy?

abdullah kahraman

@jippie freshengineer.com/blog/simple-rfid-reader-module-design

@jippie If you are talking about the following, I literally stole it:

jippie

hmm

the two filters at the top

abdullah kahraman

07:27

@jippie But thanks for saying that my blog post is nice :)

@jippie I have re-arranged its values with the capacitors and resistors I had in hand. I have found the response with trial and error using LTSpice :)

jippie

@abdullahkahraman fair enough

@abdullahkahraman other than that I was somewhat amazed by the resulting signal.

abdullah kahraman

@jippie I don't know, maybe I was lucky?

jippie

@abdullahkahraman you have to enforce luck, just like your "right of way" in traffic.

abdullah kahraman

@jippie lol

This is very interesting: lamja.com/?p=284

abdullah kahraman

08:49

Ah, you've got to be kidding me!

I was just called from Hong Kong, by a guy who has a perfect American accent who tells me that they have a firm in Dubai which sells carbon nanotubes!

And when I try to explain him why our small company will not use carbon nanotubes or why we are not interested in any financial investment on this, he got angry more and more, gradually then he shut the phone on me after saying; "You know what, we are the only supplier for this and because of that attitude you will not be able to buy this, bu they, you are from Turkey so you even don't have the money to buy it!"

I am so glad with the Google Search Engine Optimization of our company site =)

PeterJ

11:04

@abdullahkahraman, I've developed carbon picotubes that are even better if you're interested in investing.

jippie

12:14

@abdullahkahraman Yeah I bought these picotubes from @PeterJ and they're brilliant! You should definitely buy them.

@PeterJ We should discuss a provision scheme ;o)

PeterJ

@jippie, glad you are gaining the benefits of my great product. I heard because of them you were just able to purchase a $5m yacht and a small tropical island.

jippie

@PeterJ it was hard work, long days, but worth it. You're not doing to bad yourself I heard

PeterJ

12:31

@jippie, something I've been meaning to ask you might know. For a Linux SBC if you don't want to persist any data at all, ie it just does a function and you don't want to keep any logs or data but don't want any chance of FLASH file system corruption is there an easy way all the usual logs etc can be put in RAM or just not recorded at all?

abdullah kahraman

@jippie @jippie hahahhaha! :)

jippie

@PeterJ yes that is possible

abdullah kahraman

@PeterJ Are you asking this for Raspberry Pi that runs with an SD card? :)

jippie

you can disable logs, depends on the environment if that is really a good choice. Generally I don't like that because you are basically blind as to what happens on the system

you can log to ramdisk /dev/shm for example

and you can mount the flash filesystem as readonly

abdullah kahraman

@PeterJ Ooh, SBC means "single board computer"?

jippie

12:35

does need some configuring though, probably first place to look is /etc/syslog.conf or similar files (depends on the log daemon you use).

and some applications may not work properly when it can't do its own logging or keep temp files

both /tmp and /var/tmp can be moved to ramdisk, probably you need /var/run too in there

abdullah kahraman

Found out this one; cubieboard.org

jippie

@PeterJ it requires some thought, but it can be done

PeterJ

@abdullahkahraman, yes for an Olimex SBC board. @jippie I was thinking mounting read-only would cause other problems, but I guess unlike Windows it won't crash if it can't write files lol. Thanks for the pointers.

jippie

Hey there are CD based Linux systems that solved all those issues, so a SBC should be able to too

@PeterJ as said above, you probably need to redirect some paths to make it all working. There is also .. I believe a project called unionfs, which is pretty much what you need

It keeps changes in ram, and the main filesystem is readonly

UnionFS

UnionFS is a filesystem service for Linux, FreeBSD and NetBSD which implements a union mount for other file systems. It allows files and directories of separate file systems, known as branches, to be transparently overlaid, forming a single coherent file system. Contents of directories which have the same path within the merged branches will be seen together in a single merged directory, within the new, virtual filesystem. When mounting branches, the priority of one branch over the other is specified. So when both branches contain a file with the same name, one gets priority over the othe...

PeterJ

@jippie, thanks I thought there must be something like that to make live CDs work, I'll have a further look into it.

jippie

12:43

yeah cd distros use that ore something similar, there is at least one alternative, but Can't recall its name.

abdullah kahraman

13:24

Quick question:

I have an H-Bridge with both P-Ch and N-Ch MOSFETs.

My supply voltages are 24V, 2A and 5V, 500mA.

I want to drive coils of a bipolar stepper motor that is rated at about 1.5 A.

With good precautions, such as zeners and resistors and fuses, can I directly drive the H-bridge with a PIC microcontroller and also the gates of the MOSFETs with 24V?

Let's assume maximum Vsg voltage of P-Ch MOSFETs' is 12V.

I don't care about the turn-on delays and losses of the MOSFETs.

Something like the following maybe?

Perhaps for this application, since the currents are very low and the MOSFETs are at least 10A rated with TO-220 packaging, the internal body diodes can be used as freewheeling diodes, since they will not get hot at all.

jippie

13:42

@abdullahkahraman how are the top transistors driven?

abdullah kahraman

@jippie All of the labels starting with W1 - xxxx goes directly to MCU.

jippie

@abdullahkahraman Maybe I'm not thinking straight ...

abdullah kahraman

By the way, above schematic is very drafty..

jippie

at the top 24V

then a zener 6V2

then a resistor 150R

then a zener 6V2 to ground

abdullah kahraman

@jippie Oh, yes, yes, so there will always be 6V2 on the gate, doh!

jippie

13:45

so in rest there is 12V across the 150R reistor

yes

abdullah kahraman

~~W1-HL will not be able to pull down?~~

jippie

you can't pull the node voltage on the lower zener above 6v2

abdullah kahraman

I want to protect both the SG junction of the P-Ch MOSFET and the input of the MCU.

jippie

eggsplain

like in the lower half?

abdullah kahraman

@jippie lol, I guess I need a transistor to drive the upper halves..

@jippie Yes.

jippie

13:48

what is the goal for thelower left zener at W1-LL?

abdullah kahraman

@jippie In case DG junction of the lower MOSFET is shorted, the high voltage will be clamped.

jippie

@abdullahkahraman why the choice for 6V2? Why not 8V or 4V?

>! I would pick a zener voltage below the absolute maximum rating for the controller output pin. In case of a DG juction break down your controller may survive the incident.

abdullah kahraman

@jippie Dunno, I guess with 5% tolerance and current and stuff, the closest value to 5V is 6V2?

jippie

/me is out

abdullah kahraman

@jippie Thanks, bye!

jippie

13:53

and of course be careful not to load the output pin during normal operation

out

abdullah kahraman

@jippie Yes, that is my concern, too. I trust just a little bit to the internal clamping diodes below 6.2 volts.

Is this better?

abdullah kahraman

14:51

This site is cool, lol: hackertyper.net

jippie

15:18

how fast do you want C(GS) for Q1 to discharge?

@abdullahkahraman there is a reason for absolute maximum ratings. I would personally opt for 5V1

W5VO

15:45

@abdullahkahraman Your turn-off time is going to be fairly bad, and you could see issues during switching because your PFET pull-up resistor is so large (10k)

and you're going to draw a lot of current through that zener + 150 ohm resistor

jippie

16:18

Just a what if .. @W5VO: What if he moves the 150E resistor to the emitter line, then the transistor acts as a current sink, 25ish mA. Should do the job. Not sure if it is the best solution, but working from what we have.

Maybe even the better trick is to replace the 10k resistor with a current source, PNP BJT to +24V

I doubt if the 6V2 zener at Q1 is useful anyway.

Advantage of the current source at +24V is that the gate capacity is quickly discharged, while still able to pull the gate down to GND

W5VO

16:50

@jippie I don't see it doing much at all. I would rather have it right at the gate as a safety device

There are a few decent things you can do, but you're basically making your own "instant-on" power supply

and you probably need complimentary drive to keep things from cooking too much

jippie

@W5VO hmm

Is your average reference voltage in your average AVR microcontroller stable enough for a voltage measurement?

hmm .. my cat apparently figured out how to read the clock. It is 18:00 and dinner time he's telling me.

Ah internal voltage reference 2.3 - 2.8V ..

pretty useless for the idea I was thinking about

EwokNightmares

@jippie mow

The Photon

17:27

@jippie Your cat is intellectually above average. Mine get dinner at 20:00 but they always start telling me at 19:30.

jippie

@ThePhoton They needed couple months to adjust to winter time though..

/me like

51

A: Nice scientific pictures show off

Electric field due to 3 charges. The black one is a negative charge orbiting the other two positive charges. \documentclass[pstricks,border=12pt]{standalone} \usepackage{pst-electricfield} \begin{document} \multido{\i=0+15}{24}{% \begin{pspicture*}(-4,-4)(4,4) \psElectricfield[Q={[-1 3 \i...

The Photon

@jippie Some of the answers there indicate people with too much time on their hands.

EwokNightmares

@ThePhoton I wish I had too much time on my hands to do fun stuff like that

jippie

@ThePhoton yeah like me, but more the artistic kind

The Photon

@EwokNightmares If I had that much time on my hands, I would not spend it making drawings in TeX. (Not that I don't like TeX, but there are better ways to make drawings)

EwokNightmares

17:35

@ThePhoton true, but everyone falls down their own little hole if you know what I mean

The Photon

@EwokNightmares Yeah, A bunch of those drawings fall into the "If the only tool you have is a hammer..." category, though.

EwokNightmares

@ThePhoton hehe but at least he is using his tools. I get depressed if I think about how trivial everyone's holes are too much, and don't take that any other way >_>

plus some things need to be trivial before they stop being trivial

who knows he will come up with a good idea in his time with LaTeX and come up with an improvement for everyone else

jippie

18:10

@EwokNightmares I bet you can draw circuit diagrams that way, no need for circuitlab any more ;o)

EwokNightmares

@jippie maybe they can teach circuits with moving pictures as normal in the future with that man's groundbreaking latex work

jippie

there is this visualizing tool, that makes current flow on screen, not sure what the name is. "Distracting" would be a nice name for it I guess

EwokNightmares

@jippie but maybe not distracting to our evolved alien children of the future with much bigger brains

The Photon

@EwokNightmares I think from now on I will make all my schematics do cartwheels on the screen so it will be easier to read component designators, no matter what orientation they are in.

jippie

@ThePhoton nice for on a tablet

coding_corgi

18:22

Yo yo yo!

The Photon

@coding_corgi bonjour misseur le corgi

jippie

look at what the cat dragged in

coding_corgi

@jippie What cat?

@ThePhoton I have Bonjour on my mac!

Besides that I have no expierence in french

jippie

"deux grande bières" is all you need to know. Once you turn 18 and get to France with a friend

coding_corgi

@jippie ?

jippie

18:29

@coding_corgi So have you made any unintended sparks lately?

coding_corgi

@jippie Thankfully my house still stands

The Photon

@jippie "Deux billets pour Westvleteren, en Flandre, s'il vous plaît."

jippie

@coding_corgi you mean your (grand)parents house?

coding_corgi

@jippie Uh more like my parents

jippie

@coding_corgi well that's good I guess? The furniture is OK too or did it need replacement or a paint job?

/me is thinking what electronics project to do this weekend. Maybe I should ask @angelatlarge, he had a good suggestion last weekend.

coding_corgi

18:38

@jippie neither, I havent been the ee guy lately

More like trying to do hw

jippie

@coding_corgi you turned entrepreneur?

hw?

coding_corgi

@jippie that and software

jippie

@coding_corgi like what?

coding_corgi

@jippie homework, stuff teachers at school give you

jippie

oh hardware and software and no sparks

homework, righttt

yeah I like teachers

I bet I would be a good teacher myself

coding_corgi

18:40

@jippie well right now im working on this program that finds the location of the trucks from a transportation company and some other information and finds loads for the truck in that area

jippie

@coding_corgi sounds like a database (the solution for any IT problem).

coding_corgi

@jippie I'll stop you right there

@jippie Well

@jippie It's suppossed to be really current

here how i think its going to work

jippie

@coding_corgi how fast do these truck drive?

So you are developing on Raspberry PI?

coding_corgi

@jippie Well first a database is unnessecary

@jippie 55mph to 90mph(illegal)

Speed isnt important

jippie

@coding_corgi then "really current" isn't important either ;o)

coding_corgi

18:44

@jippie haha no

@jippie Well why a database

EwokNightmares

►

@24:40

does he pick something from his head and eat it?

the student

coding_corgi

I don't need to keep track of things

EwokNightmares

looks like the lecturer looks away and he takes his chance

jippie

which guy are you in the vid?

MLM

@EwokNightmares I don't see anything

EwokNightmares

18:46

hard enough to follow the guy then see disgusting stuff like that

MLM

wrong time?

EwokNightmares

@MLM well it starts at 24:40

he plays with something he got in his hair with his fingers

then he puts it to his mouth

MLM

@EwokNightmares Just saw it. Its at ~ 25:00. The guy in the audience

@EwokNightmares make a comment so we can thumb it up

coding_corgi

@jippie I can stream the the info from the website my question is how

there are thousands of lines of code

EwokNightmares

@MLM Hahaha, I feel bad for him but that is pretty gross

coding_corgi

18:48

plus i havent found and api

EwokNightmares

I don't want to take away from the video, it's really interesting

coding_corgi

@jippie here's the company: peoplenetonline.com

jippie

@EwokNightmares eew

@coding_corgi did you try the screenScraping API?

coding_corgi

@jippie wha?

jippie

sigh

MLM

18:52

@jippie lol. Just curl and regex

jippie

@coding_corgi listen to @MLM

coding_corgi

@jippie I've been out of the loop for a while, what's screen scraping

jippie

@coding_corgi ah you still haven't learned about Google in school?

coding_corgi

@jippie One thing i don't miss is your sarcasm

oh and www.lmgtfy.com

jippie

@coding_corgi I don't believe I ever used that website.

coding_corgi

18:55

@jippie Wait screen scrapes get the code or understand the code

@jippie someone around here does, im pretty sure it's you

@jippie Let me google that for you

jippie

@coding_corgi nope, my humor is better than that

coding_corgi

@jippie back to screenscraping

jippie

rewind

coding_corgi

@jippie rewind what

jippie

2 mins ago, by coding_corgi

@jippie back to screenscraping

coding_corgi

18:59

@jippie yeah, so screenscrapings gets the code or understands the code?

MLM

@coding_corgi term that describes the process that does both

coding_corgi

@MLM So this well help me by...

jippie

If you don't have an API for data from a website, you screen scrape the page and process the raw HTML data

MLM

@coding_corgi instead of a API to grab trucks you can mimic it by just scraping the page where they are listed.

coding_corgi

@jippie its js

MLM

19:02

@coding_corgi no

coding_corgi

@MLM wow ok

@MLM the code is js not html

MLM

Take for exampling PHP. You use curl to grab the html. Then you can use regex to get the values from the html

How can a page be js?

coding_corgi

@MLM that's where the code is, the html just links css and js from other pages

jippie

19:22

then you figure out how the js pulls the data from the webserver. It will be a regular GET somewhere in the code

Of course you could consult the guy who built the website if you are working for that company

coding_corgi

@jippie hmmm

@jippie can i screenscrape the js?

jippie

no you can reverse engineer the js and look at what it does to retrieve the data

then you have the data and interpret it

coding_corgi

@jippie I guess i actually have to work

bye, thanks for your help

David

20:12

Did I miss some kind of badge/award on Feb 3rd for starred chat messages?

angelatlarge

@jippie I did? That would be a first.

jippie

@angelatlarge yeah I kinda finished my USB volume controller

although the s/w can do with a decent polish job and I can enable the forth button, but I don't really have any use for the forth button and it just works the way I want.

David

@MLM Parsing HTML with regular expressions is usually not the best way to go :)

jippie

@David depends on what data you try to retrieve

I do it all the time to pull a single number from a website every morning

works like a charm

David

@jippie It's not that bad for small single values.. but definitely not the best way for anything larger

@jippie Having maintained >4k lines of code that used regex almost exclusively, it hurts my head to think of it :)

jippie

20:22

@David you do know you can comment regex's?

David

@jippie ??

jippie

at least in decent languages you can

David

@jippie Do you mean compile?

jippie

you can write comments in a regex

@David no

just like you comment regular code

David

@jippie Sure, but when you've got 10 regular expressions parsing the same data from start to finish it's far more efficient to use a streaming tree parser

jippie

20:23

i should google for that, right?

David

@jippie Especially when people try to match tags with negative lookaround, rather than making a simple xpath query

Unfortunately all the decent parsers I've used load the whole document into memory :(

jippie

48

Q: Readable regular expressions without losing their power?

Many programmers know the joy of whipping up a quick regular expression, these days often with help of some web service, or more traditionally at interactive prompt, or perhaps writing a small script which has the regular expression under development, and a collection of test cases. In either cas...

regular-expressions

you lost me at "streaming", I have no clue about "xpath" and "lookaround"

David

It's not so much the readability of the code I was complaining about

More that people will do horrible things to try and match exactly the right tag on an HTML page

(because many HTML pages are horrible themselves)

There are probably many pages online that explain why regex to parse HTML is bad better than I Could

Perhaps this -> codinghorror.com/blog/2009/11/parsing-html-the-cthulhu-way.html

jippie

I've seen some of them. I'm not really an HTML-guy so I don't come across it too often

David

:D

Time to go play on the bench for a few minutes, I'm preparing some images for a new question

MLM

21:46

@David Looks like you and @jippie already had the conversation. Xpath is quite good.

Especially when working with tables

coding_corgi

22:05

And I'm back...

David

22:41

@MLM Mmm I like xpath, but like I said all the implementations I have used eat memory :)

David

22:59

@MLM Built anything fun recently?

MLM

@David nothing finished. I am working on a simple multiplayer game.

Transcript for

Electrical Engineering