The squirrel fans used to levitate the ping pong balls inside each tube were rated at 12V; therefore, the 3.3V output of the A3BU was not enough to drive the fans. Examination of Figure 4 (see Schematics section) reveals that we used a transistor and a 12V DC power supply to amplify the driving voltage of the fans. Each fan motor was connected in parallel with a capacitor and a protective diode. The 12V DC power was connected in series with each motor, capacitor, diode set, making the motor fans in parallel with each other so that each draws an equal 12V as needed. The input to each transistor was preceded by a 220Ω resistor in series with the transistor. The signal of the transistor was connected to ground of the motor, capacitor, diode set to control how often the 12V DC was to be pulsed across the motor. Consequently, the use of an npn transistor allowed us to scale our pulse width modulation signal from the A3BU (0-3.3V) to a 0-12V signal that drives the fans.
The goal of our project was to create a visual representation of the input frequencies collected by a microphone. To do this we had to receive an analog signal from a microphone, and use this signal to drive the speeds of three different fans. After receiving the signal from the microphone, we ran the raw electrical signal through a fourier transform in order to distinguish the various frequencies within the signal. Once we had the multiple frequencies that made up our signal we divided these frequencies into 3 separate bins: low, medium, and high. We used the average of these bins in order to determine the speed at which the fan should run. If the average of the frequencies contained in the low bin increases, then the speed at which fan 1 is rotating will also increase. Fan 2 which corresponds to the medium range frequencies, and fan 3 which corresponds to the high range of frequencies, both operate in a similar manner. Our goal was achieved as we were able to get the fans to fluctuate in speed based on the various frequencies collected.