Author: rolfje

Reading an ISKRA AM550 P1 Port with a Pi

2020-01-18 rolfje 3 Comments

Although I am the guy with a soldering iron and a bit of software development experience, I am not a fan of the “internet of things”, “smart meters” or smart anything really. Not because I don’t like technology, but because of the potential security and privacy problems it brings with it. That said, because of some unfortunate events I now have a smart meter my home. So when life gives you lemons, you make Pi!

I’ve got an AM550 Smart meter with a P1 port. Seeing all the online content and suggestions about reading your smart meter, I decided to have an hour of fun trying to read the P1 data. Here’s how I did it:

Electronics, Hardware, Software

Logging in with SSH certificates

2019-06-18 rolfje No Comments

Suppose you want to provide ssh access to a server or machine without having to change the server configuration for each new user that requires acces, there is a very nice feature in ssh called “SSH Certificates”. This blogpost explains a simple setup to get you started.

Uncategorized

Travis CI and Dependabot added to Anonimatron

2018-04-26 rolfje No Comments

With new European rules like the GDPR and local variations like the Dutch AVG, interest in Anonimatron is increasing. Although I do not keep track of who is using it and where, sometimes new requirements do pop up. Recently a feature was added to Anonimatron 1.9.2 to also anonymize files.

In the wake of those additions, I planned to give Travis CI a try to automate the builds. It turns out that Travis CI integrates beautifully with GitHub, and automatically builds branches and pull requests right out of the box.

Software

1N4148 diode as RF switch

2018-02-24 rolfje 4 Comments

For a recent experiment I was using BA389 PIN diodes to switch low power RF signals. I was asked why I didn’t use an ordinary 1N4148 for that. Since I didn’t know what an 1N4148 would do when used like that, and I also didn’t really know what a BA389 actually does, I decided to do some measurements.

Read More “1N4148 diode as RF switch” »

Electronics

Even geen donor meer

2018-02-14 rolfje No Comments

“Niertransplantatiefietsen” worden ze onder artsen wel eens genoemd. Tot nu toe had je grote kans dat je de nieren, longen of andere organen van deze gezonde motorrijder had kunnen ontvangen. Zodra ik me mocht registreren heb ik gelijk aangegeven dat ik volledig donor wil zijn. Omdat ik niet geloof in leven na de dood, en wel geloof in het helpen van anderen.

Interdigital Bandpass for RTL2832U Receiver

2018-02-09 rolfje No Comments

Building a receiver for a voice repeater system in this area I set up a thumbsat receiver connected to a Raspberry Pi. The receiver is part of the repeater system to widen it’s receiving range. However, the performance turned out not to be too optimal. I guessed that the GSM and Wifi signals around here could cause the RTL2832U to overload, so I decided to build an intedigital bandpassfilter using Ajarn Changpuak‘s excelent interdigital bandpass filter calculator.

Hardware

JSON alerts for Munin

2018-01-07 rolfje 1 Comment

Munin is a great and easy way to monitor your servers. The documentation for Munin is kind of all over the place, and sometimes not all that clear.

There is the recent “Munin Guide” which is quite informative and well laid out.
Sometimes additional info and background can be found on the old munin wiki.

Getting the standard mail alerts working on munin is simplest, but as soon as you want custom layouts or send alerts as a push message to a phone, it can take quite some work. Here’s what I figured out to get the Munin alert available to you as JSON inside your own Python script so you can do anything you want with it.

Read More “JSON alerts for Munin” »

Software

Fixing a Jenkins 1.5 Slave on Windows 2016

2018-01-01 rolfje No Comments

When you configure a Jenkins 1.5x slave on a Windows 2016 machine according to the instructions on wiki.jenkins-ci.org you will probably get a warning that the .Net 2.0 is not available. This is reported as issue 21484 and the fix is to upgrade, which sometimes can be a problem.

If you can’t upgrade to the latest version for whatever reason, you can easily fix the .Net problem by changing the jenkins-slave.exe.config file from:

&lt;configuration&gt;
  &lt;runtime&gt;
    &lt;generatePublisherEvidence enabled=&quot;false&quot;/&gt;
  &lt;/runtime&gt;
&lt;/configuration&gt;

To:

&lt;!-- see http://support.microsoft.com/kb/936707 --&gt;
&lt;configuration&gt;
  &lt;runtime&gt;
    &lt;generatePublisherEvidence enabled=&quot;false&quot;/&gt;
  &lt;/runtime&gt;
  &lt;startup&gt;
  	 &lt;supportedRuntime version=&quot;v2.0.50727&quot; /&gt;
     &lt;supportedRuntime version=&quot;v4.0&quot; /&gt;
  &lt;/startup&gt;
&lt;/configuration&gt;

Hope this works for you. Cheers!

Software

Mattermost Delete Channel “fixed”

2017-10-26 rolfje 41 Comments

Users of Mattermost have probably noticed the less-than-optimal interface design where de Delete option is right above the Leave option in the Channel menu. On a busy server, you can imagine having quite a few incidents where people accidentally completely delete a channel.

In the Open Source version of Mattermost, everybody van do anything, because there is no sensible security model with roles. Mattermost Inc. seems to think that the Open Source community is not entitled to roles, which I (and others with me) strongly disagree with.

Forking Mattermost, learning Golang and enabeling security, improving a few other issues for the open source community along the way is a plan. But there is a simpler workaround for people running Mattermost inside Nginx.

Software

Installing GPG keys for Debian Backports

2017-06-09 rolfje 6 Comments

For Let’s Encrypt to automatically renew certificates on your Raspberry Pi, you probably want to install certbot. The installation instructions of certbot tell you to make use of the Debian Backports packages. Following the instructions to install backports packages into apt-get on raspbian (which is a Debian Jessie), you will probably run into the following error:

$ sudo apt-get update
...
W: GPG error: http://ftp.debian.org jessie-backports InRelease:
   The following signatures couldn't be verified because the public
   key is not available: NO_PUBKEY 8B48AD6246925553 NO_PUBKEY
   7638D0442B90D010

Software