Daniel Johnson's personal fragment of the web

Modular Conway’s Game of Life in Logisim

In CS 42 we are starting a unit on low-level computing. As a part of that, we are using a program called Logisim, a program that allows you to build virtual circuits. Of course, after experimenting with it, I had some ideas. So, without further ado, my modular Conway's Game of Life implementation in Logisim!

"Modular"? How so? Basically, I designed the circuit as a grid of cells. Each cell is a square subcircuit, and they connect to each other on the sides. There is also a clock signal that is propagated through the grid to synchronize the updates.


Shift Clock

I'm really happy with how this experiment turned out. It's a clock that spells out the time with squares, and then shifts those squares into their new positions whenever the time changes. It draws the time text into a hidden tiny canvas element at each minute, then uses getImageData to extract the individual pixels. Any pixel that has been drawn with an alpha > 0.5 is set as a destination for the next squares animation. The animations themselves are performed using d3.js.

The picture above is of the black-on-white version. There is also a grey-on-black version, if you prefer that color scheme.


Whiteboard Drawing Bot – Part 3: Editor

After completing the basic design and software for the whiteboard drawing bot, I decided to make an interactive simulator and shape editor to allow people to generate their own commands. I thought it would be cool to share it as well, in case other people wanted to play with the stroking/filling algorithms or use it to run their own drawing robots or do something else with it entirely.

For the simulator, I wrote a parser to parse the command sequence, and then animated it drawing the command out onto the screen. The parser is written with PEG.js, which I'll be discussing a bit later. The parameters for the generation and rendering are controlled using DAT.gui, and the drawing itself is done using two layered canvases: the bottom one to hold the actual drawing that persists from frame to frame, and the top one to render the arms, which are cleared and redrawn each frame. I separated them because I did not want to have to re-render the entire drawing each time the simulator drew anything new.


Whiteboard Drawing Bot – Part 2: Algorithms

In order to actually use my whiteboard drawing bot, I needed a way to generate the commands to be run by the Raspberry Pi. Essentially, this came down to figuring out how to translate a shape into a series of increases and decreases in the positions of the two stepper motors.

The mechanical design of the contraption can be abstracted as simply two lines: one bound to the origin point and one attached to the end of the first. The position of the pen is then the endpoint of the second arm:


The arms cannot move freely, however. The first arm can only be at discreet intervals, dividing the circle into the same number of steps as the stepper motor has. The second arm can actually only be in half that many positions: it has the same interval between steps, but can only sweep out half a circle. Furthermore, the second arm's angle is relative to the first's: if each step is 5 degrees and the first arm is on the third step, then the second arm's step zero follows the first arm's angle and continues at 15 degrees.


Whiteboard Drawing Bot – Part 1

For the last couple of weeks, I have been working on creating a "whiteboard drawing bot", a Raspberry-Pi-powered contraption that can draw shapes and text on a whiteboard. After four redesigns and about a thousand lines of code, I'm finally finished. Tada!

Anyways, now that I have finished building it, I am going to write a bit about how I did so in a few posts. For this first post, I'm going to be talking about the hardware behind the bot and a little bit of the software on the Raspberry Pi. Then, later, I'll talk about the custom software I wrote to translate shapes and lines into commands for the Pi.


Trying out Ableton Live

A few weeks ago, I downloaded a trial version of Ableton Live and fiddled around with it. I wrote two short songs, and I thought I may as well put them up here. So, without further ado, here are the two songs I have written:

Street Corners


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