#shrinkify

How to shrinkify an Arduino sketch onto an attiny13 chip

We needed a tree topper for the xmas tree, so I figured it was a good time to fire up the Makerbot and print one out. I found this star tree topper on Thingiverse that has space for an LED to be mounted inside: http://www.thingiverse.com/thing:14485. But why just mount a plain old boring LED when instead I could make the light fade in and out! I had an attiny13a AVR chip laying around, and I had read that it was possible to load a simple arduino sketch onto it. It sounded simple enough, but of course nothing ever is. Most of the instructions I found were for use with different chips, like the attiny45 or attiny85.

I mostly used these two sites to get the basics of how to "shrinkify" (load an arduino sketch onto an AVR chip). But there were a few major compatibility problems for the attiny13, and it took me quite a few hours of googling and testing to figure them out. (Disclaimer: I hate Google's privacy policies, so I actually run Google searches through startpage.com, which does not collect your IP or search history.) So here's the basic rundown of my steps to get everything to function with the attiny13a:

Download this package for attiny microcontroller support with the Arduino (per the instructions on the MIT site above)

Unzip it, open the boards.txt file, and add this text to the end of the boards.txt file (this will put the attiny13 as an option in your tools > board menu): attiny13.name=ATtiny13 (internal 9.6 MHz clock) attiny13.bootloader.low_fuses=0x7a attiny13.bootloader.high_fuses=0xff attiny13.upload.maximum_size=1024 attiny13.build.mcu=attiny13 attiny13.build.f_cpu=9600000L attiny13.build.core=arduino:arduino attiny13.build.variant=tiny8 (Note: If later on you find that your LED is blinking way faster or slower than you programmed it to do, you could adjust the number in the line "attiny13.build.f_cpu=9600000L", which controls the clock frequency.)

Add the entire /attiny directory to the /hardware directory in your Arduino directory (where all your sketches are stored). Directory structure  and naming matters, so make sure looks exactly like this: Arduino/hardware/attiny/ And inside the /attiny directory will be your boards.txt file and a /variants directory.

Go to your Applications directory, right click on Arduino.app, and choose "Show package contents". Navigate to hardware/arduino/cores/arduino/wiring.c. Find this text: #if defined(__AVR_ATtiny24__) || defined(__AVR_ATtiny44__) || defined(__AVR_ATtiny84__) and add a part for the attiny13, so it looks like this: #if defined(__AVR_ATtiny24__) || defined(__AVR_ATtiny44__) || defined(__AVR_ATtiny84__) || (__AVR_ATtiny13__) (source: http://tekstop.wordpress.com/2011/12/30/programming-attiny13-using-arduino-isp-and-all-the-hacking-involved/)

Plug your Arduino board into the computer, and start the Arduino software. Choose your board in the Arduino board menu (mine is an Uno).

Run file > examples > ArduinoISP

Close the Arduino app, and connect your attiny13 to your Arduino per the instructions at here and here.

Once that's done, start the Arduino app, and choose attiny13 in the Tools > Board menu. Run Tools > Burn Bootloader (it's okay if you get a couple of errors. It should have still worked.)

Open the blink sketch (File > Examples > Basics > Blink), and change the pin number to the one your LED is hooked up to.

Select Tools > Programmer > Arduino as ISP, and then upload the sketch to the chip by running File > Upload Using Programmer