Project
| # | Title | Team Members | TA | Documents | Sponsor |
|---|---|---|---|---|---|
| 34 | LabEscape Ultrasonic Directional Speaker |
Arthur Zaro Piotr Nowobilski Sam Royer |
Mingrui Liu | design_document1.pdf other1.pdf proposal1.pdf |
LabEscape Escape Room |
| # LabEscape Ultrasonic Directional Speaker Team Members: - Piotr Nowobilski (piotrn2) - Sam Royer (sroyer2) - Arthur Zaro (azaro3) # Problem Working with Professor Kwiat for the LabEscape escape room, we want to make an audio-based clue using ultrasonic waves to hide a narrow beam of audio that can only be heard at the intersection of two ultrasonic waves. We need to create the ultrasonic transducer array to emit the ultrasonic waves as well as the drivers to feed into the transducer and produce the necessary waves. # Solution We will make 2 separate subcircuit drivers to drive the ultrasonic waves. One will be a standard 40kHz wave as a reference wave, and the other will be a carrier wave using Amplitude Modulation at 40kHz to encode an audible audio signal at 40kHz. The intensity of the 40kHz wave will delinearize the air the sound is in, allowing the air to demodulate the carrier wave with the reference 40kHz wave, causing the initial audio to be heard only at the intersection of the 2 waves. For the transducer we will simply wire many individual ultrasonic transducers in parallel with one array being connected to a 40kHz sine wave, and the other connected to the 40kHz carrier wave. # Solution Components ## Digital-to-analog Converter We need to store an audio clip digitally to have the same clue play over and over throughout the escape room experience so that the clue may be discovered upon the intersection of the “audio spotlights”. To convert this digitally stored signal to a usable signal in the speakers, we need to convert the digital signal to an analog signal. The ideal resolution would be 16 bits for high quality audio as we want to minimize the distortion caused by conversion. This will be done through a DAC IC. It seems like a serial load DAC might be best as they have internal 16 bit shift registers, and if I sample my audio at 22050Hz, I can have good resolution if I load at 22050 * 16 Hz, and then move to output the signal. Components: DAC8811 - 16 bit serial Digital to Analog converter. Audacity audio software to record and encode 16 bit audio ## Modulating subcircuit We need to convert the new analog signal into a 40kHz signal using Amplitude Modulation so that the carrier wave and reference wave are at the same base frequency, and upon their crossing with enough power, the signal will demodulate in the air. We are thinking about implementing this using a digital potentiometer(s) using one of the many standard amplitude modulation circuit designs one can find online, and tuning it very specifically with those digital potentiometers based on tolerances of the resistors and capacitors used in this circuit. Components: Digital Potentiometer - MCP4141. ## Signal Amplifier Circuit After we modulate the signal, as well as for the standard 40kHz wave, we need to amplify the signal so that the signal is large enough to be powerful enough to delinearize the air for the audio signal to be demodulated at the cross section of the audio beams. Components: LM3886 (high power audio amplifier, only issue is it doesn’t have as much gain as possible at higher frequencies (40kHz), so we may decide to swap this out). ## Filtering Subcircuit A filter subcircuit may be necessary in order to reduce the noise before amplification. Given that most speaking frequencies are below 6kHz at an absolute high end and below 80Hz at an absolute low, this will likely be a band-pass filter to cut out the absolute highs and lows from harmonics and miscellaneous noise from conversion. Initially we will just try a simple first order low pass filter and high pass filter in series, which would only require a capacitor and a potentiometer to tune it. If that doesn’t do enough attenuation, I’ve found some online examples of higher order filters that will give us higher attenuation and would require a few additional resistors, capacitors, and an op amp. Components: Digital Potentiometer MCP4141 for tuning filtering circuit. Capacitors for filtering circuit. Resistor for filtering circuit. Op Amp (tbd if needed). ## Transducer Array To actually emit the ultrasonic waves, we will need an ultrasonic speaker array to emit both the reference and carrier waves. To do this we will buy several small individual ultrasonic speakers and attach them in parallel to have them all simultaneously emit the desired frequency. Components: 25+ small ultrasonic transducers (Can buy in bulk) ## Additional Component(s) Stepper motor and motor drivers for panning the speaker to align. Flashlight mounted to transducer array to make it clear the alignment of each speaker # Criterion for Success - Audio and pressure from ultrasonic waves is very narrow and intersection between the two ultrasonic “spotlights” requires precision. This beam should be consistent with the attached flashlights. - Audio is only heard at the intersection of the two waves and not too loud or too quiet. - Audio is of clear enough quality that a clue can easily be presented through the transducers. - Transducers and drivers are capable of being run for a long period of time while players try to uncover the clue associated with it. |
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