Avian’s Blog

I'm going to VCFE, München tommorow.

I was going to write something here about Galaksija's shiny new Acrylic glass case and new Galaksija tools, but I still have too many things to prepare so it'll have to wait.

So, I if you want to see my redesigned Galaksija in real life and you'll be near München this weekend, drop by. Look for Cyberpipe's computer museum.

While I use a terminal to do most of my work I do often use Nautilus to move files around and sort things into directories. It's quite annoying when I get just a lot of default "foot" icons when I'm working with files made with gEDA (which is a lot these days).

So, here's my second try at making icons:

(These icons are derived from the text-x-generic icon of the Tango base icon theme and are licensed under the Creative Commons Attribution Share-Alike license)

Update: Added icons for PCB layouts and Gerber files. SVG versions.

On Saturday I went to see Sunshine. I've read the review in the NewScientist last week and didn't expect much from it. Now, I'm surprised NewScientist even bothered to review a movie like this.

The science part of this science-fiction story is just unbelievably bad. I don't have a problem with the fact that the basic plot was impossible (there isn't nearly enough mass on the whole earth to make a device that could produce any kind of power output comparable to the sun, stars don't stop just like that, etc, etc), that is also true for many good sci-fi stories. It's the little details that really annoy me:

• They equate vacuum and weightlessness. As soon as air pressure is restored in the airlock, things fall down (I would think that anyone who passed elementary school physics should get this right).
• Mariner 10 flew by Mercury in 1973 (without any futuristic heat shielding) and didn't vaporize in an instant.
• Low temperature is the least of your problems when you are going to explosively decompress an airlock without a wearing a space suit.
• Come on, you have immersive three-dimensional displays for therapy, but the astronauts must peek through a narrow slit in their helmet?

Interestingly the basic theme of the movie (people getting obsessed with exposing themselves to the light and stuff like that) strongly reminded me of a short sci-fi story Flying toward the light by Herbert W. Franke (I only have Slovenian translation here, so the title may be a bit off). It talks about a fleet of ships from Pluto that are going toward the inner solar system in search of planets that are warmer (and trying to figure out what happened to the previous expedition). It turns out that they get so addicted to the light and warmth that they can't get enough of it and they get closer and closer to the sun until everyone looses perception and is too late to avoid crashing into the sun.

I found this two pages long story much more enjoyable and thought provoking than the whole Sunshine movie - and in the end it also doesn't turn into a cheap horror movie with rotating scalpels (??) and other sickening stuff.

A capacitor in such a sad state can still hold more than enough charge to burn out an ohm-meter.

Coming up next: repairing a Metex digital multimeter...

On a second thought, if I wouldn't destroy the instrument I would probably at some point touch the terminals with my hand and that could be a bit more serious.

Here's the final form of my ultrasonic downconverter:

It features 30 - 100 kHz input frequency range and 15 kHz bandwidth. It's a fully analog design that uses heterodyning for frequency shifting (the left knob controls the frequency of a local oscillator which is then mixed with the signal from the sensor). Output port can be used with headphones or a small speaker.

It was completely designed with free software tools from the gEDA project (and OpenOffice.org for the stickers).

The piezoelectric ultrasonic sensor is detachable so different kinds can be used (for different sensitivity and directivity).

It works surprisingly well considering my problems with noise on the protoboard. The grounded metal case really makes a big difference with such a sensitive circuit.

After a couple of walks around the house I found that the most loud things in the ultrasound spectrum are compact fluorescent lamps and motion detectors in car alarms.

Here is an interesting circuit I came across today. It's from an older "Standard Charger" for Ericsson mobile phones (in other words, it can't be used on recent models). The circuit itself is a pretty standard flyback switching power supply (240V AC input, 5V DC output at 450mA), however the PCB layout has two interesting features:

• Designer used a "ground mecca". Connections from all elements to the ground on both high voltage (left) and low voltage (right) sides radiate from one point that is near a large electrolytic capacitor. This significantly reduces noise problems in the control circuitry (I had to use the same technique when I designed a switcher last year).
• There's a feature resembling a spark gap between the high and low voltage sides. I'm guessing it is some kind of a safety feature. On both sides it is connected to ground, so perhaps it makes sure that if a spark makes a galvanic connection between the high and low voltage sides it first connects both grounds. However I'm not sure what good that would be, since the "ground" on the high voltage side may be at 380V in reference to the earth (or the unsuspecting user) depending on how the charger was plugged in.

Update: after some research it looks like this spark gap may in fact be used to protect the circuit from user not vice versa. For example if someone touches one of the low voltage terminals of the charger (which I guess may be connected to a metal phone case), it may bring the low voltage side a couple of kilovolts higher than the high voltage side (which is connected to the earth through the mains). The resulting ESD might damage the transformer or the optocoupler. The spark gap ensures that the discharge instead happens harmlessly in the air.

This is the printed circuit board for the ultrasonic down-converter I wrote about in January. Silk screen made with toner transfer came out particularly nice on this board.

I left the circuit board (with the paper stuck to it after ironing) in water over night. After peeling off the paper and drying the board there were still some white paper fibers visible. I found out that they can be easily removed with a soft pencil eraser. The result isn't perfect though and I still would trust this technique for etching, but it is more than good enough for the silk screen.

When restarting after a software crash, the Sony Ericsson P990 smart phone will print the following message:

Your phone has restarted in order to improve performance.

Best. Idea. Ever. This not only gives you a perfectly sound explanation why you lost that email you were typing for the last 5 minutes on the tiny keyboard but also gives you a warm fuzzy feeling that your phone is now even better than before. Everyone knows that you have to restart your computer when it starts feeling slow, right? So obviously this phone detects that it is slowing down ever before you notice and restarts itself. Great!

I bet that the engineer that came up with that message got a big promotion.

This a picture of the packaging of a Manhattan USB-to-parallel port adapter...

...and this is from their website:

At least they acknowledge that the information on the packaging is incorrect.