Page  224 ï~~A Touch Sensitive Dance Floor/MIDI Controller Russell Pinkston Jim Kerkhoff Mark McQuilken The University of Texas at Austin 512-471-0865/music@uts.cc.utexas.edu ABSTRACT: A prototype MIDI Dance Floor has been developed which can transmit precise position, velocity and pressure information in the form of standard MIDI messages. It consists of a large number of Force Sensing Resistors (FSRs) attached to four 4' x 16' plastic sheets, covered with thin polyethylene foam, designed to be placed beneath a standard Marley floor. The FSRs are typically arranged in such a way as to form a 16' square grid with 64 force-sensitive zones, each of which is assigned a separate MIDI Note and Continous Controller number by a 64-channel Voltage/MIDI Interface. Introduction In recent years, numerous systems have been devised for the purpose of capturing the movements of dancers and converting them into signals which can be used to control various aspects of a musical/theatrical performance. The technological means which have been utilized are many and varied, ranging in complexity from simple on/off triggers placed on the floor, to highly sophisticated systems incorporating ultrasound, radio, and real-time visual analysis. All of these systems, however, tend to reflect one or the other of two fundamentally different approaches: One approach involves what may be referred to as "passive control." It is based on the ideal that dancers should be completely free to move normally, that it is the responsibility of the system to detect their movements accurately and respond to them in an appropriate manner. Dancers using such a system would not necessarily have to be conscious of how their gestures were being used for control. Consequently, there should be no artificial restrictions on the creativity of either the choreographer or the performers. The other approach involves "active control," and it requires that the dancers be very aware of the specific effects of their movements. The ideal here is that a system should provide dancers with very precise control, allowing them to play music and/or produce sounds directly through highly specific, conscious actions. Once the dancers have learned to manipulate such a system effectively, they should be able to "play it" like a musical instrument, with much greater sensitivity and expressiveness than they could with a passive system. There are technical and aesthetic pros and cons to each approach, which are beyond the scope of this paper. The MIDI Dance Floor The MIDI Dance Floor is an experimental prototype for a system capable of being used for both active control and passive sensing, which would not require the dancers to wear or carry any special materials, and which would not be prohibitively expensive to produce. It utilizes Force Sensing Resistors (FSRs) from Interlink Corporation, which are made of a thin, flexible, and relatively strong material and are manufactured in a variety of shapes and sizes. The FSRs are very sensitive and produce a useful range of resistance which varies in inverse proportion to the amount of force applied to them. We employed a total of 128 24" FSRs, affixed to four 16' x 4' strips of heavy duty plastic sheeting, 32 per strip. 16 pairs of FSRs, wired in parallel, were attached to the plastic with contact cement and laid out as shown below. This arrangement was adopted to cover the maximum area and in order to place the solder tabs at the center of each section for protection. Wiring pairs of FSRs in parallel effectivly created-16 4-foot long FSRs, which halved the number of A/D channels required by the interface and still provided a reasonably dense number of sensors per square foot. The FSRs were then covered with a thin layer of polyethlyene 224 I C M C PROCEED I N G S 1995

Page  225 ï~~foam, both to protect them from direct impact and to help spread the force horizontally. The sections were intended to be arranged side by side, forming a 16 foot square dance area, and placed beneath a standard Marley-type dance floor, which can then be marked with glow tape to show the location of the sensors. A 64-channel Voltage/MIDI interface box was designed and built by Mark McQuilken, using a Motorola MC68HC11 microprocessor. The interface supplies each FSR with a small voltage, which varies whenever the resistance does. The 'HC11's control program tracks the signals and produces both a Continous Controller message and a Note-On/Note-off pair for each FSR. Note On/Off messages are generated whenever the voltage passes a predetermined threshold. Higher level processing of the MIDI messages is performed on a Macintosh computer using control programs written in MAX. IC MC PROCEEDINGS 1995 225 225