Simple attenuator for your home stereo

I have this nerdy problem that the output of my CD and MD player is too high and my amplifier volume halways has to stay in 7 o'clock position. To lower the volume of the CD and MD player, one can insert attenuators between CD player and amplifier.
Unfortunately those attenuators are quite expensive, ranging from 38 EUR to 55 EUR. To solve the issue, I build my own attenuators with simple RCA plug and sockets and a voltage divider consisting of a 6,8 kOhm and a 2,7 kOhm resistor, which creates approximately 10 dB attenuation. The resistors fit into the RCA plugs.
The solution works quite good. Unfortunately 10dB is not sufficient. Therefore I'm going to build 20dB attenuators soon. This requires 10 kOhm and 1,2 kOhm resistors. If you need some more information about these attenuators, here are some german forum posts: [1], [2] Approximate costs for one pair of attenuators: 2,40 EUR.

Monitor a switchport on your dd-wrt router with iptables

If you want to monitor a device within your network (i.e. to check if your printer is talking with its manufacturer), you do not need a plain old hub. You can also use the firewall of your dd-wrt router. Access your router by web-interface (and browse to Adminstration -> Commands) or ssh or telnet, and execute the following code, where you replace $IPTOBEMONITORED with the IP-Address of the device which you want to monitor, and $MONITORIP with the IP of the device which is running wireshark or some other packet capturing software.
#Add Rules to monitor a Device
iptables -t mangle -A POSTROUTING -d $IPTOBEMONITORED -j ROUTE --tee --gw $MONITORIP
iptables -t mangle -A PREROUTING -s $IPTOBEMONITORED -j ROUTE --tee --gw $MONITORIP

This will modify your mangle-table (how this works is depicted here), and tee's all traffic from and to your $IPTOBEMONITORED to your $MONITORIP.
To remove the rules, just run the follwing code:
#Remove the Rules
iptables -t mangle -D POSTROUTING -d $IPTOBEMONITORED -j ROUTE --tee --gw $MONITORIP
iptables -t mangle -D PREROUTING -s $IPTOBEMONITORED -j ROUTE --tee --gw $MONITORIP

Website Migration

After some work, this website is now running on a Raspberry Pi. The server is located in my flat and powered by solarpanels.


I switched PGP keys and upgraded to a stronger encryption. My new key has the fingerprint: 666AB60B66E715636D54CE95B526D786882B9A80 (Key ID: 882B9A80). You can download the revocation of the old key (8E073D8A) here, and my new public key block here.

FrankenDisc: use a PCGA-MDN1 MiniDisc over USB

Still I'm a MiniDisc fan. I shed some tears when Sony announced that their last device capable of using this superior medium will be produced end of this month. Recently I had the chance to aquire a Sony PCGA-MDN1 netMD player/recorder which was intended to be used in the multibay of Sony Vaio NV-Series notebooks. Some guys from minidiscforum.de already converted that device to a USB device[1]. I tried to do that myself now.

What do you need for that?
A calm hand, soldering iron and tin, USB-plug / cable, some THIN wire (I used old IDE-Connector wires, but coated litz wire is more appropriate).

Open the device by removing the four screws. Pop off the top metal cover. You can see the net-MD Drive (MZD-N1) and a Vaio Interface Connector. Carefully solder the USB plug / cable according to that specification: http://www.nord-com.net/dglander/md/sony_pcga-mdn1_steckerbelegungen.pdf to the Vaio Interface Connector. When using this connector you don't risk ruinining your precious player, but only the Interface connector. You can find images of the soldering on the page of the guy who also provided the pin-settings: http://www.nord-com.net/dglander/md/

After soldering you'll find it testing, that the normal netMD drivers are not working. Have a look on this FTP-Server: ftp://ftp.vaio-link.com/. You can find the drivers here: ftp://ftp.vaio-link.com/PUB/VAIO/ORIGINAL/NV1_DRIVERS.EXE. Unpack the exe file, you'll find a folder named NETMD. Install the drivers and enjoy your new, USB-Only MiniDisc Recorder.

Thanks to the authors at the minidiscforum for providing information on the possibilities of this modification.

External Semester Wrap Up Slides

Today is the wrap-up seminar of the external semesters in the MSc Geoinformatics programmme @ ifgi. You can download my slides here.

Air Quality Egg Workshop

The Schedule for the Airquality Egg Workshop in Münster is out! Workshop-participants might be the first people worldwide to receive an Air Quality Egg!
The Workshop is sponsored by ifgi and 52°North


The search engine SMART shall enable a "search and retrieval architecture" for sensor data (focussed on multimedia such as cameras and microphones), by using the open source search engine Terrier. SMART is going to combine sensor data with data harvested from social networks.
(via golem.de)

openelec on Raspberry PI

I just finished installing openelec on the Raspberry Pi. This tutorial released by the developers works great. The distribution works like a charm, apart from some minor issues (Weather Update Location Settings Screen does appear when beein called, but after leaving the menu).
Anyway, it seems like our pi has some thermal issues. The device does not reboot when beeing warm. I attached a heatsink to the processor let's see if it helps.

English Terms in Germany

There is a trend to give every event an english name. One of the worst terms of the last years, which will surely be used in this summer during the European Football Championships in Poland, is the term which is used to express the public presentation of a match. Someone started to use the term public viewing. The term denotes the public demonstration of a corpse.

Webservice controlled RC-Buggy

Yes. This is the answer to the question below. A video of the solution can be downloaded here: VIDEO
Visualization is not included right now, but JS-hacking should be possible. (EDIT 31.05.12: The visualistation has been included by using leaflet)

Whats Next?

After I finished my thesis, the next project will be a RC-Car controlled by Arduino.
The car will be controlled via Ethernet. Four Ultrasonic Sensors are going to sense the cars environment, whilst two old computermice are measuring the movement of the car.
The question is: Is it possible to map the cars environment and movement on a webserver running on the cars Arduino-Board?


Finished my BSc Thesis "A Web Of Things Integrated Sensor Platform For Precision Agriculture". The developed sensor platform is called AgriSenseBox.
The sourcecode can be downloaded from the following svn-repository: https://ifgi-vcs.uni-muenster.de/thesis-demuth


The SenseBox project web site is now on-line.
You can find information about the WoT integrated sensor platform here: http://sensebox.uni-muenster.de/

BSc Thesis

Alright, currently I'm working on my BSc Thesis: "A Web Of Things Integrated Sensor Platform For Precision Agriculture". ETA is mid of March.

A new year, a new design

Happy new year.