Capacitive Moments Sensing
The Radio Drum is a capacitive moments sensor. Capacitive moments
sensing determines the position of an object moving in a contained three-dimensional
space above a surface. The Radio Drum uses the "Backgammon" form of
capacitive sensing (Fig 2) to interpret the gestures of a performer.
The first moments and zero moments of are measured with a linear current
division sensing method. The sensor plane is divided into sets of wedge
shaped resistive sheets. The position of a current injected into the
resistive sheets of the Backgammon pattern is determined by the currents
that flow to equal potential corners through a chain of discreet resistors
of equal value. Operational amplifiers are placed at the four corners
of the sheet to define the terminal potentials and change alternating
current signals to voltage signals referenced to ground. The four corners
are driven and each corner acts as an antenna or receiver.