Shepherding electrons

This is part 2 of my ATtiny Mario project - part one is here  -  a Mario-type game I made for the ATtiny85 AVR as a fun way of learning about the chip.  After writing the software, I decided I wanted a nice housing for the mass of wires on my breadboards and thought it would cool to put it into a NES-style controller, which is what this post will discuss.

ATtiny85 Mario Challenge! The ATtiny85 microcontroller is a capable but compact AVR.  However with only 8K of program memory, 512 bytes of EEPROM, 512 of SRAM and only 8 pins (3 of which are dedicated to the usual suspects of Vcc, GND and RESET), it best suited to performing tasks where memory demands are not large, and only a few pins are required for interfacing.  

LCD character displays are a pretty useful addition to a project for providing a simple test output.  However if we use them in 4-bit or 8-bit parallel-mode they can be pretty greedy on pins, not to mention the software overhead with custom libraries.  I've been programming Attiny85 chips recently, where pins are certainly very much at a premium.  I wanted to add an 4-line LCD character output to the project, and luckily there are version of LCD displays that use serial inputs (I2C/UART/SPI) to control the input, meaning that if we use UART we only have to use a single pin to control output - excellent!