Sound Source Location Stand Group 72: Hiroshi Fujii Chase Zhou Bill Wang TA: Katherine O’Kane

Problem 2 Skyping multiple people can be limiting Who is speaking? Who is off of the screen? Show face to everybody

3 Condenser microphones Servo Motors Micro- controller &PCB &Power circuit Provide a way to move the cell phone camera towards sound of interest Completely automated – no hands needed Ipad or IPhone

4 ADC Arduino Raspberry Pi Servo Motor Digital Signal SPI PWM ~5 V ~20mV X 4 Adaptor Current Sensor 12V 5V 9V 120V 5V <4 V Signal Power PCB Module Motor Module Microcontroller Module 5V

Hardware Overview – Current Sensor Unit LT1494 -Current Sensor -0-12V rails -1MΩ Input resistance 5 Ethernet Adapter Schematic Ideal Frequency response

12V 300mA 3.3Vs

Hardware Overview – Audio Sensor Unit LM741 -Operational Amplifier -80mW power consumption -2MΩ Input resistance -High input offset voltage (Typ 1mV, max 5mV) 7 Ethernet Adapter Schematic Ideal Frequency response

Hardware Overview – Audio Sensor Unit 8 MCP Khz Sampling Rate -5V Reference voltage -Max 8 ch input -10 bit precision -SPI communication

Hardware Overview – Audio Sensor Unit 9 54C6 Audio Microphone -46 ± 2.0 sensitivity at 1K Hz (~20mV at 1m distance)

Final PCB Schematic 10

PCB Board Layout 11

Microphone Sensor Unit: First PCB Problems 12 DC blocking Capacitor Lack of DC blocking capacitor Amplified dc component Caused severe clipping Add DC Capacitor

Microphone Sensor Unit: Second PCB Problems 13 “Discharging” Behavior Display of discharging behavior when connected to ADC Induced by Negative amplitude “Perfect Square Wave” problem Long wire to microphone acted like antenna Mixed noise larger than the audio signal Clipping from the Op Amps 27 KHz Not the same for both 3V Bias Changing the capacitance

Testing and Verification: Filtering Audio Signal 14 Results 1.79 KHz 3.77 KHz Attenuated over 2KHz Better response to signal frequency between Hz Slight phase delay due to the phase response of filter Potential for error because unequal phase response between two PCB’s

Testing and Verification: Amplifier Circuit 15 Yellow- Unamplified Signal Green- Amplified Signal

Data Collection: Overview PCB Amplifies and filters microphone signal Sends to ADC Arduino Collects samples from the ADC Stores results in a buffer Sends to Raspberry Pi through USB Raspberry Pi Signals the Arduino when ready for new data 16

Data Collection: Design Choices Raspberry Pi ~ 4 kHz sampling rate SPI clock stops working at around 2MHz OS timing issues Arduino Can sample fast enough Memory limitations 17 SPI Clock

Data Collection: Results 18 ADC Samples from Both Microphones

Data Processing: Overview Cross Correlation Perform convolution of two signals Represents lag of signals Motor Control PWM signal determines angle Two possible implementations Feedback based control Angle-based calculations 19

Cross Correlation 20

Angle Calculation 21 Far Field Assumption Accuracy: 5 Degrees Mic Distance: 50 cm Sampling rate Necessary: 12 KHz

Software Flowchart 22

Microcontroller Schematic 23

Successful Verifications Amplify & filter audio signal Sample PCB output with ADC with 22KHz (>12KHz) Store samples with Arduino All Modules are powered Motors can accurately move Cross-Correlation algorithm Unsuccessful Verifications Conclusion Cross-Correlation with real signal Two different distortion from microphones

Conclusion: Improvements Eliminate Phase distortion Find values of capacitance that works for both boards Add filter with opposite phase response Party room problem “Hi stand” – classify audio signals Stricter thresholding – limited signal frequencies Figure out resemblance to speech vs noise 25