Markus’ Blog

Bypassing a deficient button with a high quality Cherry MX keyboard switch

by on Jan.13, 2013, under Electronics

geeky designA few years ago we bought a Soehnle digital kitchen scale. We were still happy with it if it was not for the crappy “on-tara-off” button: Within two or three months of daily use, being exposed to small amounts of flour, water, sugar powder etc., the button becomes more and more sticky. In the end, the scale doesn’t turn on or off or reset to zero when pressing the button with the usual pressure. This is an enormous drawback for usability and satisfaction.

Of course this can easily be fixed by opening the scale and cleaning the button and surrounding parts. Unfortunately the fix will only last for two to three months…

So I decided to no longer settle for temporary fixes. It is very easy to connect a different switch parallel to the original one. Being a great fan of Cherry MX keyboard switches, I went for a Cherry MX switch resurrected form an old keyboard.

(continue reading…)

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Modding an Ersa RDS 80 soldering station for more flexibility

by on Jun.04, 2011, under Electronics

Recently I decided to buy a new soldering station, mostly because I wanted to have more power for larger solderings. Being quite happy with my old one from Ersa, I decided to go for the current model RDS 80. It seemed to have a very good price/performance ratio, and I was pretty sure to get an upgrade in all regards.

PVC vs. siliconeSo I was very disappointed when I realized that the cable to the soldering iron RT 80 is made from PVC. It’s not heat-resistant, quite heavy and most of all its flexibility is not much better than that of a steel cable … How can Ersa risk their good reputation by installing a cable as bad as this one? Especially when the former products had very good silicone cables …

Searching the web, I found many people complaining about that cable but no report of someone who had successfully replaced it.
(continue reading…)

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DIY Split-flap display driving circuit

by on Jan.01, 2011, under Electronics

Split-flap display with clock
A while ago I got my hands on some old split-flap displays from a train station. Yesterday I finished driver circuits for 8 of the segments. It was only just in time to also quickly implement a clock algorithm for an extraordinary clock to display the turn of the year. Don’t miss the movie at the end of this posting.

Split-flap segments connected to driver boardsThe original driver circuits consisted of a Zilog processor, an EEPROM, an optocouppler for driving the 42V synchronous motor, transistors, two reflective IR-sensors for segment position and a few passive components. Since I do not have any information about the original interface and protocol, I decided to implement my own driver circuit and directly connect to the sensors and motor.

Split-flap digits switching

(continue reading…)

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Little Reverse GeoCache

by on Jun.19, 2010, under Electronics

A few months ago I stumbled across the very first Reverse GeoCache project by Mikal Hart. I was fascinated by the idea and decided to build one of my own.

What is a Reverse GeoCache?

Like any other GeoCache it is a box that is linked to a certain coordinate on earth. The challenge is to find this coordinate, in order to access the contents of the box.

Other than with ordinary GeoCaches you do not need to find the box at the target coordinate: You will already have it when the puzzle starts. But the box is closed and it will only open when you are near the target coordinate. In order to find the coordinate, the box has a button: When you press the button, the internal GPS receiver will detect the current location and the distance to the target will be displayed. Of course the number of trials is limited. If you press the button too often, the box will be sealed forever.

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Improved illumination for drilling PCBs

by on May.29, 2010, under Electronics

Until yesterday I was not happy with lighting when drilling PCBs: It was either too dark or there were cast shadows (of my fingers or the drill itself). So I had to concentrate hard on drilling all the holes correctly centered where they belong.


But now my problem is solved: I built a ring of 20 sunny-white SMD LEDs. It can easily be attached to my multi-tool and – as you can see on the photos – it always assures perfect light for drilling.
The first version last week was built with 10 LEDs only. I was not happy with the result then: the cast shadows of the drill were still distracting.


The LEDs are driven with constant-current of 20mA. 2 x 10 LEDs are connected in series. I built the power-supply some time ago for a different project. I plan to report on this 70-LEDs-Macro-Ringlight project (along with its power supply) in this blog soon, so I won’t go into more details now.

You can download the KiCad project files and the board layout as PDF. The layout should fit various LED package sizes, but works best with 3020. The board has a diameter of 46mm, which I consider a good compromise of good illumination and small size.

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SMD Adapters

by on Apr.18, 2009, under Electronics

SOIC-8 SMD chip in DIL-8 adapter

These days some of the coolest ICs are only available in SMD packages, e.g.

  • the fast SSP FRAM FM25256B-G and
  • the famous USB to RS232 converter chip FT-232.

For me as a hobbyist that’s a problem, because I don’t have the equipment to etch PCBs, and I want to develop my circuits on breadboards.
(continue reading…)

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2-digit RGB Geek Clock

by on Apr.13, 2009, under Electronics

2-digit geek clock

I am still not sure what project to use my rgb 7-segment display for. There were some very interesting ideas posted to the Hackaday forum. I like matthiasrs idea most: A 2-digit clock, using the red LEDs for hours, the green ones for minutes and the blue ones for seconds.

In order to get a better idea, rather then implementing it in hardware I wrote a little simulation as Java applet. Have a look and see how hard or easy it is to identify the time :-)

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7-Segment RGB-LED

by on Apr.10, 2009, under Electronics

DIY RGB 7-segement display

RGB 7-segment display

7-segment LEDs are available in red, green, yellow and blue (maybe even in white?). There don’t seem to be any in RGB though, so if you want to dynamically use different colors in your project you either have to use multiple devices or use a different technology.

So this seemed like an opportunity for a nice DIY project: Why not take an existing 7-segment display, remove the original LEDs and add some RGB ones? (continue reading…)

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Hello World!

by on Apr.10, 2009, under Uncategorized

Today I started my new blog.  I would like to post about my DIY projects, as well as about my software project JavE.

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