Step 4: Software
Since I purchased an Arduino clone (mistake), it has a different USB chip – one which is not supported natively on Mac OS X El Capitan as of now. I, not knowing this, went through a great deal of trouble figuring how to upload the Blink sketch before figuring this out. Look at the bottom of your Arduino. Look up the model numbers of both big ICs. Find the one that looks like a USB chip and get the drivers. For me, it was the CH340G.
For more details and a Mac driver, see here. Just in case that link breaks, here’s a copy. (due to limitations in WordPress, I had to attach it as an annotation in a PDF. Make sure to open it with Adobe Reader).
UPDATE: THOSE DRIVERS CAUSE A KERNEL PANIC IN macOS Sierra! As strange as this may sound, I learned the hard way that it is true. Winchiphead created a signed driver that now works, but has not yet put it on their website. HUGE thanks to Björn Sengotta for providing the drivers. Download them here. If, for whatever reason, those files are unavailable, download this file and rename it to a zip.
NOTE: You should always be extremely cautious when installing any sort of file from the internet. You should be especially cautious if it is from a random blog, and the file is not even available on the official website. However, the driver is signed, as you can see:
Once the drivers are installed, your Arduino’s serial port should begin with /dev/tty.wchusbserial (ex. /dev/tty.wchusbserial1410), and should be available under “Port” in the Arduino software.
That’s all I have now. I’m still working on the sketch and the app.