Arduino Wireless Door Bell Button

Building an Android phone connected Door Bell with Light Blue Bean’s iBeacon

The Light Blue Bean built by Punch Through Design is a versatile Arduino device with Bluetooth Low Energy (BLE) built in. The Bean’s default 3v battery could typically last a month when running a minimal sketch. A door bell button is possibly the simplest arduino device you could possibly build. A press of the button would notify an android device through BLE that someone is at the door. This post will provide an idea on how this could be built using minimal power (on the Bean) and minimal code.

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Let’s Encrypt with Exim and Dovecot

Following my post on setting up Let’s Encrypt with nginx, I experimented with installing the certificates from letsencrypt on my mail server. It was surprisingly straightforward. The key was that the verification of the domain, which requires port 80 or port 443 to be accessible on the host of the mail server. I run a secure mail server with Dovecot and Exim. Since on the server, nothing was hosted on port 80, I used the standalone plugin that runs a temporary standalone HTTP server for letsencrypt to access:

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HTTPS with Let’s Encrypt SSL and Nginx

A few days ago I enabled HTTPS and SSL/TLS on this blog. A big barrier to enabling SSL on your website is the cost of the SSL certificate and the maintenance overhead of having to constantly renew your certificate. You could already get free SSL certificates with StartSSL, but the process of obtaining the certificate is still a manual process. A few months ago Mozilla and a bunch of companies came together and created Letsencrypt, a service which issues free SSL certificates that are automatically generated with a command line tool. When set up correctly, it alleviates the need for manual intervention. As of the writing of this blog post, the service is still in beta and support for Nginx is minimal, but it’s not difficult to set up.

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How I fixed my random Visual Studio 2015 crash

For the past few days, my newly installed Visual Studio 2015 would randomly crash, naturally at the most inconvenient of times. In the 10 odd instances I could notice no discernable pattern to the crashes. It seems to happen randomly but consistently.

2015 comes with a new feedback feature in the form of smilies. You can send Microsoft a smile or a frown. I have been sending frowns every time the crash happened. Whoever opens and reads this frown would have seen my increasingly desperate messages.

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Dagger 2.0 Android migration tips

Dagger, a Java dependency injection framework, has just released version 2.0 and I thought I would try my hand at migrating my Android app, which is using 1.0, to the new version. It took me a few hours on an small-ish app with 3 activities, 6 fragments, 3 singleton services and 2 dagger modules (Application-level and activity-level). This was mostly because I used a fair bit of time banging my head against a brick war. To be fair, 90% of the conversion was smooth, but the 10% really had me lost. I will lay out some of the brick walls I ran into. The Dagger 2.0 website already have a migration guide which is good starting point. This blog post is meant to be a supplement to that.

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Docker on LXC – Use the LXC execution driver

Running docker inside LXC containers In my have proven to be no small task container, at least in my setup of a Gentoo host and Ubuntu LXC guest. One of the remaining issues is the cpuset.cpus error with Docker 1.4 and 1.5

 /sys/fs/cgroup/cpu/lxc/cpuset/cpuset.cpus: no such file or directory 

I have found a way to get around this issue.

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Bridging VirtualBox and LXC

I have a Linux box that runs both LXC and VirtualBox side by side. All the containers and VMs are set to bridge mode. Unfortunately for some reason, the VirtualBox VMs can’t talk to LXC containers. Pinging yields a response, but any TCP connection fails. Both LXC and VBox can talk to the host fine. This is how you can resolve the issue.

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Android Studio keeps deleting my project files (.iml) after a gradle sync

I had this annoying issue where Android Studio kept deleting my top-level project file (.iml) whenever I do a gradle sync. For months I had no idea why and Google search doesn’t seem to show this as a common issue. Finally today I got to the bottom of this.

The issue was the casing of the file names. For the project file, I had mixed capital and lowercase, whereas the project folder name was all lowercase. This inconsistency was due to a move of the project from a windows environment to a mac where I had a different folder name.

The fix for this issue was simple: Close the project in Android Studio and delete all the .iml files. Then use File > Import project and select the project folder and this will regenerate all the .iml files. The new .iml files should now match the case of the folder.

PouchDB for Firefox Addon SDK

I started investigating a database for my Chrome and Firefox addon yesterday and came across PouchDB. PouchDB is basically a NoSQL database for the browser. It is inspired by CouchDB and can even sync to it. PouchDB has excellent cross browser compatibility uses different backends (WebSQL, IndexedDB, LevelDB for Node.js) depending on browser or js runtime capabilities. This makes it an excellent option for cross platform web applications.

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