starlight

shipping of electronic parts from USA to europe: UPS vs DHL/FEDEX

noreply@blogger.com (Joost Yervante Damad) — Mon, 30 Apr 2012 04:55:00 +0000

When buying electronic parts it sometimes is cheaper to buy in the USA. There are some caveats concerning shipping though.

UPS

While sometimes a bit cheaper (but I usually end up with free shipping because I cluster my buys), there is one very big drawback, and that is import tax.
With UPS you have to pay the import tax in cash to the driver. Because you don't know the exact amount at order time you have to guess how much money you need to have in house and then some more because the driver usually can't give change back.

DHL & FEDEX

With DHL & FEDEX you don't pay the import tax to the driver, you get a separate bill via snail mail, which you can pay via a normal wire transfer. Much better!

Consequences

That being said, this starts to influence my buying choices. For example digikey usually ships with UPS, while mouser allows me to choose FEDEX, which makes mouser my preferred choice for buying parts from the USA.

When buying in Europe it doesn't matter so for farnell and rsonline I don't mind either. If I can buy at either of those I still prefer that but both digikey and mouser have a somewhat larger and different selection.

Others

I basically buy most parts at those 4, and sometimes sparkfun or one of sparkfun's resellers of course. Are there any other shops you recommend ?

3D printing a LED diffuser directly on PCB

noreply@blogger.com (Joost Yervante Damad) — Thu, 26 Apr 2012 19:28:00 +0000

"3D printing a LED diffuser directly on PCB"

Yes, it is possible. Hence this quick blog post.

This lamp is a simple proto PCB with a whole lot (>30) of high brightness 0603 white LEDs soldered on them with a few layers of 3D printed yellow PLA on top of them.

I had to add some DRAM heat-sinks to the back to deal with the massive heat production, especially given that PLA gets liquid at relatively low temperatures. Light production is quite poor, but it is cool for mood lighting.

To be continued.

3D printing and openSCAD

noreply@blogger.com (Joost Yervante Damad) — Sun, 01 Apr 2012 06:28:00 +0000

Yesterday, March 2012, I gave a short talk about 3D printing and openSCAD at Newline^2, the conference at 0x20.

The slides and embedded pictures are available under the Creative Commons Attribution-ShareAlike 3.0.

Click here to get them as PDF.

Arduino, limited RAM and PROGMEM

noreply@blogger.com (Joost Yervante Damad) — Sat, 10 Mar 2012 07:13:00 +0000

And so I was happily adding more and more descent error handling code to a piece of code running on an atmega328p (the Atmel AVR micro-controller also typically used in Arduino). And then the thing started acting up. Now I've had that happen to me before so I immediately thought that it was running out of RAM.

The atmega328p has 32k flash, which is typically plenty, but it has only 2k RAM, which is not very much at all.

I was doing things like:

Serial.println("FAIL invalid argument");

Now, you might be thinking, why does it have to store the "FAIL invalid argument" in RAM?
It has all to do with how braindead C/C++ is/are.

"FAIL invalid argument" is a "const char *" which although it seems read-only it actually isn't (and no "const char const *" isn't either).
Thing is in C it is perfectly legal to cast away any types and just start changing characters in the string.
And the compiler can't know you're not doing that as you could be doing it via some very scary indirect pointer arithmetic to get to the characters in the string.

Bottom line is that every "constant" string in the code is copied to RAM because it could theoretically be used.

Now, on to PROGMEM.

It is a way to use strings directly as contained in the program code, but without the copying to RAM.

Okay, I'll first give the short answer which works fine on arduino 0.22 or newer:

Serial.println(F("FAIL invalid argument"));

This does some casting and other magic in the back and does the right thing.

Just for educational purposes lets take a look how to do it without arduino tricks.

the <avr/pgmspace.h> header contains a useful macro, called PSTR which looks like we could use it just like this:

Serial.println(PSTR("FAIL invalid argument"));

Unfortunately that doesn't work. PSTR returns a PROGMEM pointer and it turns out (even though the atmega has a flat address space) we can't use PROGMEM pointers just like regular pointers.

It will nicely compile and give garbage.

The only way is copying the data from PROGMEM to RAM and then using it.

This could be done byte-by-byte with pgm_read_byte (this is what arduino does internally, take a peek in arduino-1.0/hardware/arduino/cores/arduino/Print.cpp ) or to a buffer in RAM with strcpy_P.

All this is quite awkward and error-prone and makes me long for a nicer language for microcontrollers ;)

arduino mega and multiple hardware serial devices

noreply@blogger.com (Joost Yervante Damad) — Fri, 20 Jan 2012 18:16:00 +0000

For a project I use an arduino mega (Atmel AtMega1280 8-bit micro-controller to be precise) to access multiple other hardware devices via hardware serial.

I'm running the Arduino stack on the hardware, more specific the arduino 1.0 release.

Now the atmega1280 (or atmega2560) has 4 hardware serial devices (called Serial, Serial1, Serial2, Serial3 in arduino) so using multiple serial devices is easy eh?

Not really.

For one use case I have a device connected on Serial1 at 57600 baud.
I want to be able to route serial traffic from that device to the Serial device connected to the PC.

Sounds easy enough, the follow arduino sketch does the job:

void setup(){
  Serial.begin(57600);
  Serial1.begin(57600);}
void loop() {
    // from external device to serial console
    if (Serial1.available() > 0) {
        byte incomingByte = Serial1.read();
        Serial.write(incomingByte);
    }
    // from serial console to external device
    if (Serial.available() > 0) {
        byte incomingByte = Serial.read();
        Serial1.write(incomingByte);
   }
}

Thing is, for short messages this works fine. However for longer messages only one direction is stable, the direction from the external device (Serial1) to the serial port (Serial).

I could run the serial port (Serial) at a slower speed then the device (Serial1). However then the other way around will start to drop bytes!

Let's have a look at HardwareSerial.cpp as provided in the arduino distribution.

It seems to work with an RX and TX buffer for each hardware serial device.

#define SERIAL_BUFFER_SIZE 64

Maybe that buffer is not large enough. The AtMega1280 I'm using has 8K SRAM and thats quite some more then I need. Let's double the buffer.

#define SERIAL_BUFFER_SIZE 128

Surely the behavior is somewhat better, but it is still dropping bytes in one direction.

Let's have a look at the write function.


size_t HardwareSerial::write(uint8_t c){
  int i = (_tx_buffer->head + 1) % SERIAL_BUFFER_SIZE;
   
  // If the output buffer is full, there's nothing for it other than to 
  // wait for the interrupt handler to empty it a bit
  // ???: return 0 here instead?
  while (i == _tx_buffer->tail)
    ;
   
  _tx_buffer->buffer[_tx_buffer->head] = c;
  _tx_buffer->head = i;
   
  sbi(*_ucsrb, _udrie);
 
  return 1;}

Look and behold:

while (i == _tx_buffer->tail)
    ;

it's a busy loop! If Serial1's transfer buffer is full the entire micro-controller will block and this keeps happening all the time.

The solution I introduced is only move data from one serial device to the other when both are ready. One should be readable (available() in arduino jargon) and the other should be writeable.

A writeable function is not available in Arduino so I added the following method to the HardwareSerial code:


bool HardwareSerial::writeable(){
  int i = (_tx_buffer->head + 1) % SERIAL_BUFFER_SIZE;
  return (i != _tx_buffer->tail);}

The loop from the sketch now looks like this:

void loop() {
    if (Serial1.available() > 0 && Serial.writeable()) {
        byte incomingByte = Serial1.read();
        Serial.write(incomingByte);
    }
    if (Serial.available() > 0 && Serial1.writeable()) {
        byte incomingByte = Serial.read();
        Serial1.write(incomingByte);
   }
}

This helps in the sense that it smooths the flow between the serial devices.

No more dropped bytes!

X with xmonad without KDE/gnome, continued

noreply@blogger.com (Joost Yervante Damad) — Mon, 18 Jul 2011 15:49:00 +0000

This is the setup I settled upon in the end, it's working great. It has heavily based on this wiki page.

The .xsession file:


#!/bin/bash

# Load resources

xrdb -merge .Xresources

# Set up an icon tray

trayer --edge top --align right --SetDockType true --SetPartialStrut true \
--expand true --width 10 --transparent true --tint 0x191970 --height 12 &

# Set the background color

xsetroot -solid midnightblue

# Fire up apps

xscreensaver -no-splash &

if [ -x /usr/bin/nm-applet ] ; then nm-applet --sm-disable & fi

if [ -x /usr/bin/gnome-power-manager ] ; then sleep 3 gnome-power-manager & fi

#xset b off

eval `gpg-agent --daemon`
eval `ssh-agent --daemon`

setxkbmap -option compose:caps

exec xmonad

In order to have X execute the .xsession isof starting the window manager itself, choose the "System default" as session type in gdm or kdm.

This is my .Xresource file:


# red cursor Color, looks great in combination with xmonad
xterm*cursorColor: red

# save tons of lines
xterm*saveLines: 100000

# triple click like in konsole/gnome-termimal
xterm*on3Clicks: regex [^ \n]+
xterm*on4Clicks: line

# use fancy terminus font
xterm*FaceName: terminus-10

This is the .xmobarrc file:


Config { font = "-*-Fixed-Bold-R-Normal-*-13-*-*-*-*-*-*-*"
, bgColor = "black"
, fgColor = "grey"
, position = TopW L 90
, lowerOnStart = True
, commands = [
Run Weather "EBDT" ["-t"," C","-L","64","-H","77","--normal","green","--high","red","--low","lightblue"] 36000,
Run Cpu ["-L","3","-H","50","--normal","green","--high","red"] 10,
Run Memory ["-t","Mem: %"] 10,
Run Swap [] 10,
Run Date "%a %b %_d %H:%M" "date" 10,
Run StdinReader
]
, sepChar = "%"
, alignSep = "}{"
, template = "%StdinReader% }{ ancalagon %cpu% | %memory% * %swap%    %date% | %EBDT%"
}

ancalagon is the name of my laptop.

Finally, this is the .xmonad/xmonad.hs file:


import XMonad
import XMonad.Hooks.DynamicLog
import XMonad.Hooks.ManageDocks
import XMonad.Util.Run(spawnPipe)
import XMonad.Util.EZConfig(additionalKeys)
import System.IO

main = do
    xmproc <- spawnPipe "xmobar"     xmonad $ defaultConfig         { manageHook = manageDocks <+> manageHook defaultConfig
        , layoutHook = avoidStruts  $  layoutHook defaultConfig
        , logHook = dynamicLogWithPP xmobarPP
                        { ppOutput = hPutStrLn xmproc
                        , ppTitle = xmobarColor "green" "" . shorten 50
                        }
        --, modMask = mod4Mask     -- Rebind Mod to the Windows key
        } `additionalKeys`
        [ ((controlMask .|. shiftMask, xK_z), spawn "xscreensaver-command -lock")
        , ((controlMask, xK_Print), spawn "sleep 0.2; scrot -s")
        , ((0, xK_Print), spawn "scrot")
        ]

With big thanks to John Goerzen for providing the excellent information.

configuring X with xmonad without KDE/gnome

noreply@blogger.com (Joost Yervante Damad) — Sun, 10 Jul 2011 10:41:00 +0000

While configuring X11 to use the xmonad tiling window manager instead of the more usual KDE or GNOME, some things were somewhat less then obvious, and I document them here.

.xsession configuration

These are settings that all can be made permanent by adding them to the
.xsession file in your home directory.

disable CAPS, enable Compose

setxkbmap -option compose:caps

Now you can use the Caps Lock key to compose special characters. E.g.

<Caps> 'e gives é
<Caps> e= gives €
...

... and as a bonus you can't accidentally press the Caps Lock key any more!

disable beep globally

xset b off

start gpg-agent on startup

eval `gpg-agent --daemon`

start ssh-agent on startup

eval `ssh-agent --daemon`

other things

dmenu

Install the suckless-tools package for dmenu among things.

Just use <alt>-p to quicklanch apps with dmenu.

xterm

I want to use plain xterm as terminal emulator as the tabbing of gnome-terminal and konsole is rather pointless in combination with the tiling.

The default font size was to small. To solve this I did a dirty hack like this:

update-alternatives -config xterm and change it to uxterm to have an UTF-8 terminal by default
edit /usr/bin/uxterm and change the last line by adding -fn 10x20 to it.

email

At the moment I'm still using kmail as email client (and accidentally akregator as RSS feed agregator). I'm still thinking about switching that as well.

... to be continued ...

one month with a makerbot thing-o-matic, some musings

noreply@blogger.com (Joost Yervante Damad) — Fri, 01 Jul 2011 07:34:00 +0000

I've been meaning to write up more about my learning experience with the makerbot thing-o-matic 3D printer, but for now a short summary is already better then nothing:

construction

I bought the printer as an assembly kit from robosavvy.co.uk. It took me about 12 hours spread over about 10 evenings to build the printer. Had to redo a few steps, some steps were not very clear. Should've made notes of that but didn't. Guess I was to eager to finish!

shortage of wire

One issue I had is that some cables were to short to fit comfortably and be able to survive the movement of the printer platform. I extended them with some wire I had lying around.

printing

Finally after finishing the construction I installed the software, did basic calibration of the machine and did a first print. It actually somewhat worked already!

calibration

After some playing around I noticed the Z axis motor got really hot, soo I did a full calbration as described
at http://wiki.makerbot.com/thingomatic-doc:calibration . This solved the heat issue.

ABS & warping

I started printing with the roll of black ABS supplied with the printer.
These are the relevant settings:

platform temperature: 125°C
heater temperature: 225°C

Printing goes fine but the plastic warps really easily. This is due to the ABS getting solid again really fast as it cools down.

PLA

I ordered some PLA from german supplier 2printbeta. PLA is a compost-able plastic that is made from corn waste and has some interesting properties. The most important one is that PLA doesn't get solid as fast as ABS as it cools down. This seems to avoid warping all together. PLA also comes in beautiful transparent variants.

These are the settings I use for the PLA I bought, but be sure to check the recommendations of the vendor:

platform temperature: 75°C
heater temperature: 195°C

PLA and higher temperatures

Some people recommend using PLA at way higher temperatures like 235°C. This is really dangerous as the PLA will become liquid all the way up into the plastic transport part of the printing head and could bond to the plastic up there. I had to re-assembly the head after I tried that.

plastic not moving anymore

One of the most common issues is that the plastic is no longer pushed down in the head. This could be because the nut got loose due to excessive shaking of the printer, but I also had another issue:

Z-axis calibration

This is vitally important. The Z axis should have a correctly configured max height.

The issue I had was that the max height was slight altered due to moving the machine around a lot and this caused the head to start printing too close to the platform. This causes pressure to build up in the head and the stepper-motor starts skipping. If this happens to you be sure to check the Z-axis setting!

white plastic

For some bizar reason both the white ABS and white PLA I have causes the stepper to skip at times. I don't know why yet but for now I'm not using white plastic anymore.

modelling

Of course in the beginning it is fun just to print the calibration cubes and stuff found on thing-i-verse but after a while I wanted to start making something myself.

It was quite a bummer to find out that google sketchup doesn't work under Linux. Then I found openSCAD, which is a declarative programming language for constructing objects. It works quite ok for simple things.

conclusion

I still have a lot to learn about 3D printing. Documentation is quite sparse still.
It is fun and I already made some items that are in use.
The thing-o-matic printer requires a willingness to maintain the machine or it will give issues.

bread maker hints and tips

noreply@blogger.com (Joost Yervante Damad) — Fri, 08 Apr 2011 06:55:00 +0000

Since a couple of years I have the excellent Panasonic Automatic Breadmaker.
The quality of bread it produces easily matches and with some help surpasses the quality provided by the bakery. Here are a few hints that help make the experience better.

Use more water!

A 1kg bread based on 600g flour typically requires between 360 and 380 ml of water. I always use 400ml. This makes your bread a bit stronger and it'll dry out less fast.

Use less salt

You can easily get away with 4-5gram less salt then the recipe requires and it'll still taste great.

Ready-made flour mixes

There is nothing wrong with using ready-made flour mixes.However in my opinion they tend to contain to much salt and tend to produce bread that is quite light in structure. I prefer stronger bread.

The solution is adding some other non-mixed flour like rye. For example I typically replace 600g of mix with 150g rye and 450g mix. It's not needed to add any extra salt or yeast. The bread will still rise fine.

Pizza!

The bread maker also makes dough and the pizza dough is highly recommended. It only takes 45 minutes in the machine to make a nice dough. That being said, if you have more time I recommend making the dough earlier and letting it rest a while in the fridge.

Enjoy.

young deer,early morning

noreply@blogger.com (Joost Yervante Damad) — Wed, 06 Apr 2011 08:20:00 +0000

debian, grub2, booting the "other OS"

noreply@blogger.com (Joost Yervante Damad) — Wed, 06 Apr 2011 07:58:00 +0000

Recently my debian installation switched to grub2 and the boot menu no longer showed a working entry for booting my old XP partition.

The solution is simple:

sudo apt-get install os-prober
sudo update-grub

From now on grub2 will automatically detect and add to its menu all other OS partitions on your local disks.

blog moved

noreply@blogger.com (Joost Yervante Damad) — Tue, 05 Apr 2011 17:10:00 +0000

I my blog moved again, looks like some posts got republished to planet grep, my apologies for the spam.

Joost

digicorder and recording subsequent programs

noreply@blogger.com (Joost Yervante Damad) — Sun, 22 Aug 2010 06:19:00 +0000

Digital television is getting the norm in Belgium, and typically people rent a "digicorder" from the TV provider. This allows you to watch television and also record programs for later consumption.

In practice my family only records a few programs and watch them later. It's very convenient not to be bound to a specific schedule. (On the other hand it would probably be cheaper to just buy the DVD boxes of the series we like instead of having television at all, but that is another discussion :) ).

In general, the digicorder works fine, I have one big gripe with it though: recording of subsequent programs.

Lets say we're recording subsequent programs A and B from channel 0. Let's assume there is some advertisement in between programs. This gives as timescale something like this:

Now, there are three ways the digicorder can record the program, not counting the completely faulty ways when timing goes all wrong.

Both programs want to record a time-slice before and after their program, but this goes wrong in the middle, and only one recording ends up with the middle part.

correct

The correct recording is with the break point in the middle like this:

I presume there are not some kind of markers in between the broad-casted programs on commercial television because it makes their advertisement store even worse.

Therefor, in practice you typically end up with one if these two:

B in recording 1

This is problematic because if you don't remember not to erase recording 1 after watching program A, the start of program 2 will be lost.

A in recording 2

This is even worse. Lets say you want to watch program B first.

You first have to open recording 1, fast forward all the way to the start of program B, start watching and after a few minutes switch to recording 2. This will also leave recording 1 marked as "watched" even though you didn't watch program A yet. More confusion!

A simple solution

In the end this is a simple technical problem with an even simpler solution: record the overlap in a separate file and make it part of both recordings. Visual:

If you watch recording 1, you get recording 1 + X. If you watch recording 2, you get X + recording 2.

If you erase recording 1, X stays. Only if both recording 1 and recording 2 are erased, X gets deleted.

More in general there will be X areas both in front and at the end, etc...

Would be nice if the biggest TV provider of Belgium could implement this. If the digicorder was open source I would've done this already months ago...
I guess I'll have to look into some kind of MythTV like setup one day.

morning vs evening

noreply@blogger.com (Joost Yervante Damad) — Sat, 14 Aug 2010 06:59:00 +0000

Morning (dew)

Evening (rain)

young tomato

noreply@blogger.com (Joost Yervante Damad) — Wed, 21 Jul 2010 08:13:00 +0000

From 2010

valeriaan

noreply@blogger.com (Joost Yervante Damad) — Wed, 21 Jul 2010 08:12:00 +0000

From 2010

arduino-0018, avrdude and usbtiny programmer

noreply@blogger.com (Joost Yervante Damad) — Sat, 17 Jul 2010 18:38:00 +0000

For some reason the avrdude binary that is shipped with arduino-0018 has no support for the USBtiny programmer which I use to burn bootloaders on blank AVR atmega328 microcontrollers.
On Debian the workaround is simple: first install avrdude via apt-get/aptidude and then enter the hardware/tools directory in the arduino-0018 dir and replace avrdude by a softlink to /usr/bin/avrdude like this:


$ cd arduino-0018/hardware/tools
$ mv avrdude avrdude.old1
$ ln -s /usr/bin/avrdude .
$ mv avrdude.conf avrdude.conf.old1
$ cp /etc/avrdude.conf .

After this burning a bootloader via the menu in arduino works fine again. A similar approach will probably work on other Linux distributions.

digitalis 2

noreply@blogger.com (Joost Yervante Damad) — Mon, 07 Jun 2010 18:41:00 +0000

digitalis 1

noreply@blogger.com (Joost Yervante Damad) — Mon, 07 Jun 2010 18:40:00 +0000

papaver

noreply@blogger.com (Joost Yervante Damad) — Mon, 07 Jun 2010 18:37:00 +0000

check my coachwork

noreply@blogger.com (Joost Yervante Damad) — Mon, 07 Jun 2010 18:34:00 +0000

amavisd-new clamav crashes tmp files

noreply@blogger.com (Joost Yervante Damad) — Fri, 07 May 2010 14:30:00 +0000

Since I still run my own mail infrastructure, I also run anti-spam and anti-virus on it.
Today I noticed that free space on my server running lenny was ALOT less then usual. Turned out that clamav was crashing all the time causing lots of temporary files in /var/lib/amavis/tmp.

An upgrade of clamav also stopped the crashes.

While at it I also disabled quarantining virus mails, I never had to retrieve any mail out of there anyway...

Nokia N82 Bluetooth + GPRS/3G

noreply@blogger.com (Joost Yervante Damad) — Fri, 12 Feb 2010 06:39:00 +0000

A few months ago I did an interesting discovery about using my cellphone to go on the internet via bluetooth. I had this strange situation before where it just stopped working, and after revisiting all configs it worked again.

What really happens is that my cellphone somehow crashes, after which I power cycle it by removing the batteries. The phone then boots again, but here is the twist: the service channels in the phone are re-allocated and apparently in a random order!

This implies that the RFCOMM channel configured in the /etc/bluetooth/rfcomm.conf file is possible wrong now!

Solution: just browse the services again with sdptool browse, adapt the file and it should work again!

Ochtendzon, Grote Nete

noreply@blogger.com (Joost Yervante Damad) — Sun, 31 Jan 2010 06:50:00 +0000

Ochtend zon aan de Grote Nete in December 2009.

Morning sun, grote nete

noreply@blogger.com (Joost Yervante Damad) — Sun, 31 Jan 2010 06:46:00 +0000

December 2009, Morning sun at the Grote Nete.