Building a flaglight for my recumbent bike

A few months ago I had a test drive on a recumbent bicycle and was instantly hooked. Suffice it to say that a few months later I am the proud owner of one myself. Being the cautious cyclist I am, my top priority especially on a recumbent is visibility. The bike is quite low, my head is around 1m of height, for me coming from an upright that’s low. Therefore visibility means adding a bikeflag. The one I went for is quite big and reflective. Nevertheless I’d still prefer some active visibility. The shop I ordered the flag from also has flaglights but basically it’s three LEDs for 70€. Knowing the material cost must be in the one-digit euros I found it hard to go for it. Especially since it is designed for bike dynamo operation requiring extra weight and extra money to be put into the bike as well. I planned on using battery operated lights already in my possesion so I don’t need dynamo equipement or cabling.

Long story short: I over-engineered the whole thing and now I want to show it off. My choice of LEDs are 4cm long chip on board bar-shaped LEDs. I got one white and one red so I would be visible both from front and back. Both are 300mA versions so I can connect them in series. Because the voltage regulator promised PWM brightness regulation so I added a controls to the handlebar to remote control brightness and allow for blinking. The LEDs are glued to a hand-milled aluminum carrier and covered by transparent heat-shrink tubing against the weather. The control electronics are also covered by heat-shrink tubing. The switch should be weatherproof given that it’s one meant for motorcycle use. Power is supplied by a weatherproof box with four 18650 lithium batteries. Remember that the pictures below are taken in daylight — When it is dark the light is pretty bright and the movement of the flags makes it even more visible.

Nevertheless I tend to drive way more defensive on the recumbent than on the upright. I wonder whether it’s more safe than the upright due to my defensive driving or still more dangerous because it’s so low.

Arduino and battery pack attached to the bike rack
Arduino and battery pack attached to the bike rack
Battery pack and arduino on bike rack
Battery pack and arduino on bike rack
Flag with light from the back
Flag with light from the back

Flag with light from the front
Flag with light from the front

Control on handlebar
Control on handlebar


Using those dipswitch-controlled rf switches with home-assistant

I really wanted to use these cheap RF switches with Homeassistant. Unfortunately the rpi-rc library needs an integer number to know what to send for the switch to switch. I didn’t have an RF receiver so here’s a script that can convert between the 10 bit dip switch setting on the back of the plug and the integer needed for rpi-rc:


!/usr/bin/env python3
 import argparse
 def codify(code):
     return code.replace("0", "00").replace("1", "01")
 parser = argparse.ArgumentParser(description='Sends a decimal code via a 433/315MHz GPIO device')
 parser.add_argument('code', metavar='CODE', type=str, 
                     help="zeroes and ones from the dip switch ('up'=1, 'down'=0)")
 args = parser.parse_args()
 code= args.code.replace('1','3').replace('0','1').replace('3','0')
 code_off= codify(code+'00')
 code_on= codify(code+'01')
 print("off: {}".format(int(code_off, 2)))
 print("on:  {}".format(int(code_on, 2)))</pre>


run it like so (with zeroes and ones for the dip-switch setting, example for the pictured switch) to get the integer codes for on and off:


python 1010110000
off: 1115472
on: 1115473


afterwards you can use the integer codes for on and off with the integrated scripts in rpi-rc (or home-assistant):


rpi-rf_send -g 5 1115472


Running wordpress in docker

The wife now also starts a blog. Time to play: This blog here is still set up the old-fashioned way, php and mysql running on the web server. But setting up a wordpress for her gives me a welcome excuse to play with docker.

So there you go:

For the simplified creation of vhosts for docker containers I set use a trio of containers using a slightly-adapted version of this docker-compose.yml:

  • nginx as reverse-proxy
  • jwilder/docker-genfor automatic creation of v-hosts based on container environment variables: simply pass -e and this container adapts the vhosts config for nginx accordingly.
  • jrcs/letsencrypt-nginx-proxy-companion to also automatically fetch a letsencrypt certificate and enable ssl for the new vhost..

For the wordpress instance I run an adapted docker-compose.yml for the usual container pair of wordpress and mysql. Apart from keeping the wordpress instance in a directory volume (for easy fiddling) i added the following modification:

       VIRTUAL_HOST: <vhost-1>.de,<vhost-2>.de...
       LETSENCRYPT_HOST: <vhost-1>.de,<vhost-2>.de...
       LETSENCRYPT_EMAIL: <letsencrypt-mail>

This enables automatic creation and sslification of the vhost in the nginx reverse proxy.

The nginx-reverse-proxy solution really makes it very convenient to just spin up a new container and immediately use it with a valid SSL certificate. Definitely worth the time for initial setup – it does not take longer than setting up SSL manually but you only have it once to get SSL for all vhosts.

Using duofern roller shutters with homeassistant

Zur Deutschen Version des Textes.
I use homeassistant as a front-end for home automation. It is really hackable, written in python and comes with support for a lot of devices. I chose it initially because it has mysensors support.

Last year I needed a solution for controlling roller shutters. Sadly most manufacturers that market in Germany are pushing their own proprietary solutions for home automation. While homeassistant supports a few of those via the proprietary gateways of the manufacturers, the gateways themselves can be very pricey. Additionally the installed roller shutters were belt-operated and the shutter was mounted in a steel case above the window. Unfortunately the hatches giving access to the roller shutter were so small that I ditched my initial plan of mounting a tube motor in the shutter roll.

Finally I found that german manufacturer Rademacher sells wall-mounted belt motors for Roller shutter operation (“Rollotron”). Some of these can be remote-controlled via “duofern”, a proprietary remote control protocol by the manufacturer. While homeassistant does not come with out-of-the-box support for this protocol, the Perl-based FHEM home automation project has support for these blinds via a usb stick sold by the manufacturer.

Duofern USB stick

I loathe perl, therefore I ported the rollotron-related sections of the GPL-licensed FHEM implementation to python. My python port can currently be found as pyduofern on bitbucket.

There is some documentation on how to get it to work with homeassistant in the subdirectory examples. Luckily the RF communication goes both ways, so homeassistant displays the current position of rollershutters regardless of whether they have been moved with manual controls or via homeassistant.

The whole thing is work in progress – in order to get it natively into homeassistant the next step would be to add it to pypi, but before I do that I would rather have it working with asyncio, because that is the way to do it for homeassistant.

Manually setting firewall rules for the Synology DSM openvpn interfaces

I keep forgetting how to do this so I’m finally gonna write it down. Synology DSM does not allow you to define arbitrary firewall rules. I especially want to define more paranoid firewall rules attached to openvpn connections. Sadly the GUI does not know about selective firewall rules for these so I had to do it myself. Synologys openvpn client calls


once the connection is established and


on disconnect. To define my own firewall rules I figured I would have to add to these two scripts. Unfortunately synology only sets its firewall rules some time after the scripts have run. So when I just add my own firewall rules to the two scripts, they are overwritten seconds later by synologys firewall. My solution is the following: at the end of the synology scripts




I add my own firewall setup script via:

# above here is synologys original code
# save the return code of the synology ip-up/down logic

# call my script and send it to the background
nohup /opt/bin/ &

# pass the original return code to the calling process
exit $returncode

In my own firewall script I begin with:

sleep 10

before I proceed to remove the synology firewall rules and replace them with my own.

WARNING: DSM Updates may overwrite your custom settings. Whenever you update DSM make sure that your settings are preserved.

Vectorized vortex clock

Dr Who style vortex clock
SVG (click to enlarge)

The Doctor Who intro features a vortex clock. Find it on youtube here (left of the two clips). I went through some pain to vectorize it in halfway decent quality in preparation of building a Doctor Who themed wall clock. In case anyone else wants an SVG version here is my amateur attempt. I know a lot could be done to make the SVG way smaller (probably the image could easily fit into 1/10 the size). My main goal was to get something that prints decently with a laser printer to iron on an aluminum plate, and this SVG is sufficient for that purpose.

Dynamic pdfs with pdflatex and ocg-p

Ever since I saw the microtype manual, I wanted to have something similar. The amazing thing about it is that you can switch on and off different microtype options and observe the resulting PDF output,

I now found the package ocg-p which allows to generate pdfs with dynamically switchable layers similar to the above. I built a demonstration which switches between a greek epigraph and its translation by clicking.

The code I used is the following, you can find the resulting PDF output here. The dynamic features only work in dedicated PDF readers (try opening with Acrobat):

\tikzset{external/export next=false}

\begin{tikzpicture}[node distance=3cm,every state/.style={fill=green!20},auto]
\draw[opacity=0] (-5,4)--(0,0);
\node[anchor=south east] at (0,0) { \toggleocgs{greek german}{I know that I know nothing}};
\node[anchor=north east] at (0,-0.2) { \toggleocgs{greek german}{\textit{Socrates}}};
\draw (-2,-0.1)--(0,-0.1);
\node[anchor=south east,font=\selectlanguage{polutonikogreek}] at (0,0) { \toggleocgs{greek german}{Οἶδα οὐκ εἰδώς.}};
\node[anchor=north east,font=\selectlanguage{polutonikogreek}] at (0,-0.2) { \toggleocgs{greek german}{\textit{Σωκράτης}}};
\draw (-2,-0.1)--(0,-0.1);


Running an open WIFI hotspot in Germany

logo by The Tor Project
logo by The Tor Project

German legislation makes it difficult to run an open WIFI hotspot: Not only will the police possibly search your house if somebody decides to commit criminal acts using your connection, you will also be liable via Störerhaftung for copyright-“crime” committed using your connection.

Despite the difficulties I am a big fan of offering open WIFI, and there is a large Café right across the street from my house which does not offer free WIFI on their own. Recently it hit me: Why not just make it a TOR hotspot? TOR is a free, strong anonymizing network run by volunteers like me. Data is redirected over three encrypted computers, making it impossible to trace data back to the users computer. If the Internet connection from the open WIFI passes through TOR nobody’s gonna ring my doorbell if somebody misbehaves.

Said was nearly done: used a Raspberry PI 2 I had so far no use for and combined it with a high power usb-wifi-adapter from amazon. After that it was only a matter of following the onion pi tutorial (but opting to run hostapd without encryption).

If you decide to do the same please consider doing it like I do: run a middle relay or a bridge on your pi in parallel to the access point (unless you pay per traffic) to give back to the TOR network that you use. Middle relays and bridges do not allow others to access the web from your connection, so they are quite safe to run even on a home connection.