New hosting provider

Due to the inability of my previous hosting provider to maintain the integrity of their machines, resulting in enormous and incomprehensible technical problems for at least a year now, I have decided to switch over to another provider.

To complete the chaos, this page will from now on reside under the new TLD


For the sake of existing links to this page, I will keep the old domain ( transparently mapped to the new URL for at least one year while this page will already deliver all content in relation to the new domain.

I expect the transition to go smoothly (most of it already has) and hope for better conditions in the future – especially regarding server features and page loading time.

Please don’t hesitate to contact me if anything remains broken. You’ll find my details on the Impressum page, or you can just hit the comments section of this post.

Sony TA-F220

These are just some short notes I took while inspecting an aged Sony TA-F220 amp some days ago. I have seen several of these over the last years, pretty decent amp with a nice sound. They all have some regular aging flaws in common, though.


Fig. 1: Top-down view inside the TA-F220.

[Read More]


Another +1 added to my count of curiosities and eastereggs hidden in electronic devices. While pulling apart blown power bricks for cheap ferrite cores, I stumbled across a novel, environmentally aware concept for the line isolation barrier (click pictures for large version).

fish01 fish02

Seems to work, no fried fish was the cause of this failure. Worth a smile ;-)

NOTE: The soldering work does not actually look that bad. Part of that goes to the strong lighting for the photo and part to the blown smoothing capacitor spraying its contents everywhere due to overvoltage in a bad three-phase installation (L1/N exchanged).

Acer K330 LED beamer repair

This article is about one of my recent spontaneous projects. A few days ago, I got lucky on an ebay auction and picked up a broken Acer K330 beamer. I often look for these kinds of offers because I have spent several years in the audio/video repair business and am pretty confident in my skills when it comes to fault-finding. So I figured, saving some money by restoring a broken device couldn’t hurt.


Fig. 1: Acer K330 power supply and optical path.

First some facts and features: The K330 uses a three color LED module, which promises a long lifetime and low energy consumption. A Texas Instruments DLP module handles image generation. In sum this lets me hope for good contrast and strong colors, even if the brightness of 500 lumens doesn’t seem that much. An interesting thing about this DLP chip is that it uses an uncommon diamond pixel grid for size reasons. Diamond in this context means that the pixels do not form a rectangular pattern like in the usual TFT monitors but rather a grid of 45° rotated and slightly squeezed, not completely rectangular tiles. Of course, this means that internal resampling has to occur to map the image from the rectangular domain onto the diagonal domain of the IC.

So, this projector was obviously broken when it arrived – what a surprise. The seller had already informed me that it had suffered from overvoltage of unknown cause. The VGA picture was supposed to be very green-ish, the HDMI input dead in whole and the media player erratic. A slight flickering in the picture was also mentioned. I’ll take you through the repair process for this device from here on. [Read More]

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Wacom digitizer screen

Anyone who has already tried to use some kind of tablet device for writing should know that there are fundamental differences between screen types.

The most common is the capacitive type, where you use a finger or some kind of conductive pen to write on a glass surface, while the touchscreen device captures movement of the capacitance change through a grid of transparent electrodes on the backside of the glass. This works, but it sucks for writing precise text or drawing sketches. You can find these screens in almost every modern smart phone, tablet PC or kitchen appliance. They are cheap!

Next is the resistive touchscreen, where a small, hard point presses down on a plastic surface. The touch element is composed of two pieces of clear foil, coated with a conductive material. While the two layers stay isolated when there is no pressure applied, the pen forces them together in a certain point, forming a conductive path. By knowing the specific resistance of the surface coating, the circuit can determine the position of the pen tip by measuring path resistance from different edges of the screen. This type was pretty popular in PDAs (which have by now been fully replaced by smart phones, what a shame ;-) ) as well as the almost equivalent navigation assistants – and is not that common anymore. Writing performance is fair but not exceptional, though.

The third kind is the most interesting one. Real tablet PCs (the ones with the flip-over display) have this normal-looking pen with the nylon tip, which you can use to accurately write on the glass/plastic display surface. Many even feature some buttons on the pen, some kind of eraser on the backside – and they are damned accurate! They have another thing in common: Most of them use technology by a company called Wacom, also producer of digital writing and drawing pads for artists.

This type is called a “digitizer screen”, and it uses a sensing panel *behind* the actual display to recognize and track the pen. The digitizer panel contains an amazing set of surface coils to provide an alternating magnetic field through the screen. Inside the pen, there is a resonant circuit which uses the field energy to transmit the button states and even pressure on the pen tip back to the coil. By monitoring the strength of the resonance through different surface coils, the digitizer then calculates the position of the pen above the surface. In other words, you get a high-res info about the pen position (easily above 25.000 points resolution along the surface edge, depending on the digitizer type!), you know the pressure applied, button presses on the pen and even where the pen is when it is not yet touching the surface.

I recently disassembled a trashed tablet PC (Toshiba Portege) with a broken motherboard for interesting parts, and came across this:

tablet01The LCD panel is a LTM12C328T type. Attached to the backside is a SU-010-X01 tablet pen digitizer, and the marking on the ICs clearly suggests that it is made by Wacom. This would make a fine graphics tablet – but how to attach it to any other PC? [Read More]

Shiny parts: Laser diode

During disassembly of some old CD/DVD drives, I stumbled across a pair of *really* beautiful laser diodes. Not much use for them right now, except practicing macro shooting – pretty hard to get good pictures of the structures inside and the dichroitic filter blue at the same time.

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TSOP as a proximity sensor?

A few days ago, a friend came over to talk about some microcontroller related projects. One of the topics was distance sensing, or rather proximity/movement sensing with low technical effort.

The basic idea was to detect movement of an object or person within a short distance to trigger events. Typical sensors for this kind of application would be passive infrared (PIR) modules, radiowave sensors (microwave or radar) or active infrared distance sensors. All of these can be quite pricey, perhaps with the exception of the PIR, which cannot detect objects very well.

So, I thought about how the goal could be accomplished with standard parts. Active infrared is the most simple choice. [Read More]

Array microphone

So…it’s been a while. Somehow I thought, I’d have finished the CNC writeup by now, as well as my plans for continuing work on my plasma-bar meter project. Things turned out different.

I got into my Bachelor’s thesis after completing the preceding seminars, which kept me busy since june ’13. The topic is centered around signal power based speech DOA estimation using directional microphones, very interesting stuff from the domain of signals processing. I had a very interesting time learning lots of new things, and somehow I also wanted to get hands-on with the matter since attending several advanced DSP courses during the last two terms.

While working on the thesis, I realized that microphone array systems are really nice things to have to play around with. I decided to make my own, which I did in my free time in parallel to the thesis. Let me at least show some pictures as long as I still don’t get around to working on other stuff.

A few technical details follow below.

[Read More]

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CNC finally running

The CNC mill got into a working state right before christmas eve. I know it’s not a present in that sense, but still! :3

Some parts of it are still fixed with a lot of glue and tape (or zip-ties ^^), but for now that’s perfectly sufficient. Right now. it can already mill hard wood and MDF, so I will be redoing some critical parts that lack in precision and/or quality before I write up the whole project as one. Unfortunately, I fear that the original plan about using an (older) EPIA 800 board as a controller can not be followed, EMC2 just refuses to start on that thing. Grrrr…

More pictures and text will follow in a few day’s time. Until then, enjoy the holidays and have a nice and safe start into the new year!

Oh, right, and two Stellaris Launchpad eval-kits from TI that I ordered back in September arrived JUST ON the 24th. How great of a timing is that? I don’t care about the wait, it was well worth it and I knew up front – but thanks again to the girls and guys of the TI support, for solving all the technical difficulties along the way :-)

PBG12201 plasma displays

Bar display with reservoir cap in HV circuit

I picked up some unusual plasma displays from ebay some weeks ago, which I have been searching for quite some time now. The picture above shows an illuminated Burroughs PBG-12201 plasma bargraph display. They are pretty hard to get by now, and if available, prices are a real shocker. Some shops in the US that carry them ask for 230 USD and some even more. Sometimes they appear on ebay for about 50 USD, but you have to be real quick to get some. Best chances are with surplus stores that sell off leftover production stocks or disassembled devices that originally contained such tubes. A few very retro and very popular mixing consoles for audio applications used them as main VU meters (eg. made by Lexicon),  as well as some current professional grade standalone meters (eg. RTW, one of those is where I first saw such a display and was absolutely fascinated by the deep orange hue). As they eventually get old and start flickering or burning in if not properly cared for, spare parts have become rare, and since Vishay – the most recent producer of these displays – has discontinued the product line in early 2012, I would expect the market to dry up even more.

Mine were obviously scavenged from some kind of device by a Hungarian ebay seller, he offered some 10+ pieces of the PBG-12201 type display for 8 Euros each – a real steal! I just couldn’t resist and got myself three of them, together with matching sockets. Thinking back, I don’t get why I ordered three instead of four…oh well, it’s done. The tubes show some signs of wear, like glass chipped off around the edges and burn marks on the cathode traces, but they all work fine. [Read More]

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