I'm not exactly sure where the idea for this Halloween costume came from, it really emerged from my workbench when a bunch of parts each of which i had some code for, were in sight all at once.
Half a dozen table-top drinks vendings machines were being discarded at work (in accordance with the WEEE requirements of course), each of which had a parallel GLCD screen in. A Pacific Display Devices 12864-12 STN GLCD with T-6963C controller.
I managed to get one of these GLCD going on an Arduino Uno using the u8glib (https://github.com/olikraus/u8glib/). Sadly these particular LCD screens required a negative 9-12V bias for contrast. I needed a project to use these for, and beyond messing about with some graphical stuff, and showing the temperature reading from an LM35, I didn't really do much.
At some point we dabbled with a balancing robot, an IMU with PID. The motors lacked encoders, and we were relying on the closed loop control being good enough. It got my interest in quadrature decoding which I hadn't touched in a decade. That skewed somewhat from motors onto rotary switches as an input mechanism for UI control. I still intend to make a USB HID device with these to replace my broken Griffin Powermate (http://www.griffintechnology.com/products/powermate/)
I purchased a few Rotary Encoders from sparkfun (https://www.sparkfun.com/products/10982/) and got down to work. Used some example code for an Arduino Uno, which functioned satisfactorily, but having an entire Uno for this job seemed over the top. The search was on for a solution in the form of an 8pin MCU. The ATTiny25/45/85 seemed like a winner. I found TQED on GitHub (https://github.com/renbotics/TQED) which did the job nicely, I forked it to add functionality (https://github.com/DougBarry/TQED). As these rotary encoders are RGB, I may get round to using an ATTiny44 (more pins) or similar to drive the RGB LED one day.
Some time ago I purchased a pulse sensor from Cool Components (https://www.coolcomponents.co.uk/pulse-sensor.html) to play about with. It sat idle in my random bits pile for some time.
When you put all these bits together, the obvious outcome is a wearable heart rate monitor with bonus video games, right?