Getting Started with Embeded Elixir on Nerves

Screenshot of testing code

In his talk at CodeMash this year, Joel Byler mentioned a platform named Nerves which quickly and easily packages up Elixir projects for embeded applications. Joel said the platform boots in seconds, the framework takes care of all the low-level tasks, and the tooling handles all the work required to convert Elixir applications into embeddable firmware. It sounded too good to be true, so I had to try it out.

Getting up and running was actually super easy; I installed Nerves and built my first app in minutes. And, it did boot up incredibly fast, but that first app didn’t actually do anything. I needed to get my device connected to the wireless network so that I could start doing more interesting stuff, and that is when I ran into problems. I have a Raspberry Pi 2 which doesn’t have built-in WiFi, so I have a TP-Link TL-WN725N USB adapter. Unfortunately, Nerves Raspberry Pi 2 system only supports Ralink RT53xx (rt2800usb), RealTek RTL8712U (r8712u) and RealTek RTL 8192 (rtl8192cu) devices.

My first thought was, “I guess I will have to get the latest Raspberry Pi Zero to get this thing working.” Maybe I just wanted an excuse to buy a new little toy, but I’m supposed to have technical skills, so I shouldn’t buy my way out of this problem. Besides, I have used the TL-WN725N adapter in the past and I knew that there was a Linux driver for it. The question was, how do I get that driver installed in Nerves? Here is how I made it work.

Testing the Rails

A new year, a new programming language. I have recently started developing web applications using Ruby on Rails, rather than React+Redux on Flask+SQLAlchemy+Sqitch on Python. I’m enjoying the relative simplicity; it allows me to focus on creating complexity in other places, places where it will actually help me produce more features in less time. One area where I like to do more with less is in tests. No one likes to spend coding time writing tests, but it makes development easier and more productive in the long run, so it’s an absolute requirement.

One project I’m working on has an administrative area which is only accessible to privileged users. I needed to write test which ensure privileged users get access and everyone else does not. I could just fill in the default Rails generated tests for the authorized user, then copy and modify them for unauthorized users, but that becomes tedious if I want to check more than two roles.

Screenshot of testing code

Literally a Single Page App

Inspired by a few talks I saw at CodeMash, I wanted to perform some experiments with React. I just wanted to focus on the React code, not set up build pipelines, so I wanted a single page app which was literally a single page (except for the Javascript requirements, of course). Below is the template I used for my experiments. It is super simple, all it does is source react.development.js, react-dom.development.js, and babel-core from CDNs. I just wanted to document it so that I don’t have to look it up in the future. At the bottom of the page is a larger example which includes some actual React code.

  <script crossorigin
  <script crossorigin
  <script crossorigin
  <script type="text/babel">
    // React code goes here
  <div id="root"></div>

You would not want to use the in-browser babel script for production code.

Open Sourcing My iOS Apps


A few months ago I let my individual Apple Developer Program membership expire. I have been working on other projects and have not given enough attention to my iOS apps, and though they still worked, I had not updated them in a very long time. The apps were starting to look dated, and were certainly not taking advantage of the latest development frameworks. So, I decided to stop paying Apple for the privilege of keeping outdated free apps in their store.

Rather than just letting my apps disappear, I decided to open source the code so that other people might be able to use it. The apps are written in Objective-C and C, so that may limit interest in it. But, someone may be interested enough in the seam carving algorithms to deal with the archaic languages.

Trip Report: Minister Creek

Located in Pennsylvania’s Allegheny National Forest, Minister Creek is a great trail for introducing new people to backpacking. It is not terribly difficult and it is perfect for a single overnight stay. So, when Heather said that she would be willing to try backpacking with the boys, our new puppy, and me, I knew this would be the best place to go.


Rocky Mountain National Park
Rocky Mountain National Park

Ncurses based System Performance Monitor for Mac

nmond screenshot

Nmond is a Ncurses based system performance monitor for Darwin (Mac OS X terminal) written in pure C. It was “forked” from nmon. The original nmon gathered system statistics by looking at /proc, which is not available on Darwin, so system calls had to be implemented for all the statistics. The original program was monolithic and used global state a lot; it was modularized during the rewrite. It’s still a work in progress.

Simple Microprocessor Design

Simple-12 CPU This details the hardware design for a simple 12-bit microporcessor. I created it for an undergraduate class which I took a few years ago. It is not really usefull for anything besides learning how computer hardware works, but I still think that it is pretty cool. I found the documentation for it on my hard drive and remebered how proud I was to have actually completed it; I am a computer scientist, not a computer engineer. Simple logic gates are used as the basis for the creation of more complex digital electronic circuits; those circuits, including a control unit, are in turn connected via a datapath to form a completed processor. The processor datapath is designed to implement the Simple-12 instruction set.

Battleship AI Algorithm Using Dynamic Programming

(image via Wikimedia)

My boys and I enjoy playing a mobile version of the classic battleship game when we are waiting our turn at the barbershop. However, the artificial intelligence algorithm this specific game uses is so feeble that even my youngest son can consistently beat the computer player. So, I started thinking about improving the algorithm. I searched the web to see if there was already an established, dominant algorithm. Although I found several clever implementations, including one that used probabilities and another based upon a checkerboard pattern, I did not find one that I particularly enjoyed. After thinking about the problem further I came to the conclusion that this problem would be well suited for a dynamic programming algorithm.

From my perspective, the best approach to take when searching for the opponent’s ship is to target a square that is in the center of the longest line of unmarked squares. It would be even better to find a target which is at the intersection of two long lines of unchecked squares. To me, this is an effective divide and conquer approach similar in spirit to the concept of binary trees, the problem is finding an efficient algorithm. The problem seems to lend itself perfectly to the dynamic programming approach.

The Ballpoint Pen

Although their use is slowly fading due to society’s increased reliance upon computers, the ballpoint pen is still used on a daily basis by most people in the United States. What is now an inescapable piece of disposable technology began its life as nothing more than an expensive and seemingly short-lived fad. Popular media accounts from the mid-1940s track the ballpoint pen’s rapid initial increase in popularity followed by its similarly precipitous drop. After this initial popularity spike the media chronicled the ballpoint pen’s gradual rise from novelty to ubiquity.

On a trip to Argentina in the summer of 1945 a businessman from Chicago named Milton Reynolds discovered a fascinating pen that he was certain could be a commercial success in the United States. Reynolds brought some of the pens back to the United States with him, and within a few months they were being mass produced by his newly formed company.