At Rest	Circuit Board and Sensors	In Motion [MOV, 0:30]
Robotic Finger Awareness, Action, and Interaction; Two Weeks; Spring 2004 I built a motorized finger designed for expressive motion, controlled using a light sensor and a touch sensor.

Problem
Build something that incorporates a motor and which responds to sensor input.

Approach
As a musician, I'm interested in products that have appropriate and expressive mappings between input (hitting, blowing, plucking) and output (insert favorite noise here). I began thinking about the kinds of motor-driven motion resulting from inputs. Cranes, diggers, lifters, robotic arms, and the like create mechanical motion driven by physical input in the form of levers and buttons. Could a set of inputs for these devices feel as expressive as a musical instrument? Would the resulting motion seem more expressive?

I began by intending to build a robotic arm, but decided instead on a finger. When we consider human motion, we can be expressive with our arms, but we actually are most often expressive with our hands and fingers. Pointing, scratching, tapping, curling – all are highly communicative actions. The smaller relative size of a finger also gives a sense of intimacy that an arm lacks, increasing the likelihood of it seeming expressive.

Solution
I built the finger using sections of oak dowels connected by springs, which acted as joints. Two strings threaded through opposing sets of hooks along the length of the dowels, each attaching to a servo motor located in the housing behind the finger.

A BASIC Stamp microcontroller connects the motors to two sensors. A photoresistor controls the motor pulling the upper string, which controls the finger's up-down movement. A force-sensing resistor maps to the bottom string, which curls the finger.

I considered using the same type of sensor for both controls, but after some experimentation chose the photo and force-sensing combination instead. The photoresistor detects light levels – in this case, a hand obstructing the ambient light – while the force sensing resistor is pushed, or better yet, picked up and squeezed like a coin. This pairing of no-touch and high-touch sensors creates a more expressive means of controlling the finger; despite the different mappings, they are easy to use together.