AkaPi: A Nim repository from Dhertz

AkaPi is a 16x256 RGB LED display running of a Raspberry Pi 2 model B. Currently it scrolls multiple images created by different scripts querying web APIs.

Technical Detail

The display is actually made up of 8 Adafruit 16x32 LED Matrices daisy chained together, all running off two five-volt ten-amp power supplies (they can draw a lot when on bright white apparently, though I have not tested it).

It is made up of two distinct parts:

There is low level interface to output values to the displays via the Raspberry Pi's GPIO and the RPi-RGB-LED-Matrix library, with a custom drawing engine on top. If you are interested in how the displays work, I suggest starting here. This part reads in the simple images and manages the scrolling and updating the images in memory. It also updates the animations (see below) to the next frame.

Also, we have a daemon written in Nim to generate simple PPM images (basically a large matrix with rgb values for each pixel) with new data from different web apis on the Raspberry Pi.

Why insert immature fashionable language?

I chose to use nim because I wanted to use one of these fancy new compiled languages, but really like writing Python. Nim seemed to be the best way to satisfy both of these, as well as produce a (hopefully) faster binary than running multiple python scripts at once. Nim also is strongly typed, but has type inference, which is really cool. I really like the super powerful macro/templating that I can do, as I made a template to create threads that act on a document fetched from a URL repeatedly.

 template recurringJob(content, waitTime: int, url, actions: stmt) {.immediate.} =
   block:
     proc asyncJob():Future[void] {.async.} =
       while true:
         let content = try: getContent(url)
                       except: "Failed to retrieve URL:\n\t" & getCurrentExceptionMsg()
         try:
           actions
         except:
           echo("Failed to run actions:\n\t", getCurrentExceptionMsg())
 
         await sleepAsync(waitTime*1000)
 
     asyncJob()

Which would then be called like:

 recurringJob(document, 600, "http://example.com"):
   let json = parseJson document
   echo json["key"]

Nim also allows for me to really easily create a cross compilation toolchain for the Pi, so I can make compilation very quick for ARM compared to compiling natively.

Compiling the code

Nim

To compile the Nim, you need to have a secrets.nim in the same directory as main.nim. This is not included in the repo as these secrets should not be public.

Here is mine without the tokens:

const
  FORECAST_IO_KEY     = "xxxxxxxxxxxxxxxxxxxxx"
  MBTA_KEY            = "xxxxxxxxxxxxxxxxxxxxx"
  twitterAppPubTok    = "xxxxxxxxxxxxxxxxxxxxx"
  twitterAppPrivTok   = "xxxxxxxxxxxxxxxxxxxxx"
  twitterOAuthPubKey  = "xxxxxxxxxxxxxxxxxxxxx"
  twitterOAuthPrivKey = "xxxxxxxxxxxxxxxxxxxxx"

You will then need to download and install nim (the compiler) and nimble (the package manager) to get the required dependencies and install your platform's SDL1 developement package.

Finally, run nimble install to install the dependencies and nake x86-build to produce the binary.

C/C++

To compile the C++ you should just need to cd into the c_src directory and run make.

Current information displayed

The AkaPi Logo
Next Trains at Kendall T stop
Next EZRide buses from outside 8CC (afternoons only)
Current stock price and performance
Weather for the next few hours and when to leave for lunch/home based on chance of precipitation.
Purple dayz
Twitter replies to the @AkamaiPi account
Euro 2016 scores from yesterday's and today's live/FT matches

Animations

Animations are made up of multiple frames (ppm images) named 0.ppm, 1.ppm, etc stored in the animations/$ANIMATION_NAME directory. There can also be a file inside the directory named animate.conf that contains the number of milliseconds each frame should be shown for. The format of the file is

frame_pause $NUMBER_OF_MILLISECONDS

this should be the first line of the file as all other lines are discarded. If there is no animate.conf present or it cannot be parsed, a default of 100ms (10 frames per second) is used.

Example animation directories can be found here.

The animations loop and scroll across the display like the other images, but, unlike the static images, animations are not updated while the program is running.

Current Animations

Pac Man being chased by ghosts - source
Nyan Cat - source

Previous information displayed

District and Circle Line trains out of South Kensington station
Superbowl XLIX average point spread, as reported by ESPN
2015 Ashes Test Series scores (Cricket scores for England vs Australia)

Wishlist

Quote/Fact/Lie/Joke of the day
Add notifications to scroll down from the top
WebUI

To Do

C

Fix so it doesn't leak like a sieve
Find annoying crash
Fix cutting lines of the beginning of images
Removal of images from hash
Refactor animation code into functions
Alphabetise includes

Nim

Cache
- more - I already save the previous string, and we do not update the sign if they are the same
Make prettier (output and code)
Make weather more concise

Dhertz/AkaPi