Previously I mentioned that I’m interested in photocell sensors and repetitive motion, since they are very simple and intuitive. However there are also limitations: Photocell sensor is a type of analog output that only sends one dimensional data output. Comparing to a motion sensor that provides you three dimensional data output (x, y, z), what you get from a photocell sensor is really a stream of number within a defined range. There are also limitations from repetitive motions as human input: if there is no specific purpose associates to it, the motion itself can be meaningless. Such issue was clearly shown in my previous blog that even there is a intuitive connection of the graphic shape changing with the motion.

Originally I spent quite amount of time seeking for a connection between repetitive motions and fractal geometry. However even we build up an interaction that we can grow fractal with certain repeating motion, it is still a bit… dry. A major issue for me is the vague relationship between human input and graphic output. Fractal as a type of geometry formation, is so rigid for interaction that it is not clear to me: what exactly are we interacting in this case? I believe a key problem here is a lack of meaningful connection between human motion input and digital output.

When there is no meaning for a motion, we assign motions with some power of control or communication. When there is only one parameter, we can introduce randomness and simple game theory into our game design that such single parameter playing a role as a balancing point. So I pivoted my thoughts and started to think: what kind of interaction can we create with limited input and how it can be natural, intuitive, and interesting? To create an interaction with a single variable, I need to design a gaming system to make our motion input with some kind of control effect, and the control, has to be linked to a goal so the whole interaction will has a purpose and motivation.

Therefore I designed a following gaming mechanism: The goal is to catch the most flying balls with a circle during a limited time, by calibrating the size of the circle and the balls. In each iteration there will be a ball starts flying from a random position at the bottom of the screen, and it shifts position when flying up to the top. The circle, also appears in a different position each time, and the user has to move their hand to change the size of the circle to catch the ball each time. If the centroid of the ball is *(x,y)* and center of circle is (*x1, y1)*, we catch the ball when:

*(x1-x)^2 +(y1-y)^2 < (radius of circle)^2,*

then we append one point to our score.

The control system is that we adjust the photocell analog read to calibrate the size of circle and size of flying balls. If the serial output as *m*, the radius of circle as *R* and radius of ball as *r, then we develop such relationship:*

*R is a function of m, while r is a reversed weighted function of m.*

However there is a ‘cost’ of enlarging circle, that the flying ball will shrink smaller when you have a larger circle. In this way, I used one single serial input to create a conflict (or balance if you prefer) between probability of circle to catch the ball versus probability of the ball avoid to be caught. So here is a question for you: what would be a optimized parameter for you to use, so that the circle is big enough while the balls are not too small at the same time?