CirlceBoy is a small circuit board that lets you replace the directional pad on a gameboy or other device with an analog joystick. CircleBoy was designed specifically to use the 3DS circle pad with a gameboy, but is adaptable to tons of use cases.
A gallery of my installation of the board can be found here.
You can select between 4 different modes for the stick. Modes are selected by shorting out the dpad contacts in the appropriate direction when you turn the system on. The configuration is stored in the EEPROM of the chip, so you only have to set it once.
| Direction | Deadzone | Segments |
|---|---|---|
| Up (default) | Small | Balanced |
| Down | Large | Balanced |
| Left | Small | 3/4 Straight, 1/4 Diagonals |
| Right | Large | 3/4 Straight, 1/4 Diagonals |
Since this project uses the reset line on the ATtiny85, once you've written the firmware and enabled the NO_GOING_BACK_NOW macro, you'll need to disable the reset on the chip. I did this on my Mac with
/Applications/Arduino.app/Contents/Java/hardware/tools/avr/bin/avrdude -C/Applications/Arduino.app/Contents/Java/hardware/tools/avr/etc/avrdude.conf -v -v -v -v -pattiny85 -carduino -P/dev/cu.usbmodem143301 -b19200 -Uhfuse:w:0x5f:m
The important part of that is setting the hfuse to 0x5f.