The proximity antennas sense the physical presence of one’s body and convert the ‘closeness’ of the person to each antenna into voltages that can be used to control synthesizers, computers, lights and even robotics. The design is based on ideas gleaned from Robert Moog, MIT, the Moskow State University and many other sources, then honed by my experience.
The two antenna sensing units each have a vertical 4.5 foot long copper pipe attached to a resonator that is enclosed in a shielded box. That box sits upon a marble base plate that has a conductive film applied underneath. This plate radiates a high frequency sine wave signal from a master oscillator that is picked up by the copper antenna.
The antennas work on the principle of using body capacitance, as small as femtofarads, to change the frequency of a resonator built into the base of each antenna. As one approaches the antenna, the body capacitance effect increases as the distance decreases and so the frequency of the resonator falls. As the frequency of the antenna resonator gets closer to that of the sine wave radiator, the resonator produces more output voltage. This voltage is conditioned by outboard circuitry to produce a common analog control voltage, from zero to five volts. Thus, the closer one gets to the antenna, the more control voltage it produces.
The control voltages from each antenna are continuously monitored by an Arduino Uno to produce a gate or trigger votage for each antenna. Variable controls are provided so that the gate can be made to turn on when the person is at a certain fixed distance from each antenna. So if the distance threshold is set to be 2 feet, then anytime a person’s hand is within 2 feet of the antenna the gate or trigger will be active. This gate voltage was used for triggering synthesizers in our initial performances, but it can also trigger a sound file to be played, ring a bell or start a fountain.
It is important to note that the antennas are not Theremins. They are just general-purpose controllers that convert distance into control voltages. Their application is limited only by the imagination of the user.