Wireless Motion Capture Mid-Year Design Review Seth Berkowitz Dean Howarth Eric Marklein Ashesh Rastogi Advisor: Professor Daniel Schaubert

Project Overview Optical motion capture confines to small area Self referencing system gives user freedom of motion Find distances and calculate 2D position Base Units Remote Unit

MDR Specifications “Wireless Ruler” – 1 dimensional static distance measurement Transmit wave between remote and base units (breadboarded) Digital acquisition of raw data SRAM storage of raw data Offline algorithm for distance calculation

PDR Flashback Phase based distance measurement Two frequency transmission from base Up-convert at remote unit Retransmit to base Ultrasound vs. RF

Microcontroller Phase Comparator Temperature Sensor Clock MUX Memory Free Space Address Data R/W Trigger Phase Diff Transmit Transducer Receive Transducer Amplifier Zero-Crossing Detector BPF System Block Diagram Computer Interface

Analog Zero Crossing Comparator To Phase Comparator BPF BW = 377kHz Transmit transducer Clock MUX Receive transducer Non- Inverting Amplifier Free Space Schmitt Trigger Buffer

Received Signal

-Transducers 14 cm apart -3V square pulse wave

Phase Comparator

f transmit f receive D CLK RESET Q D CLK RESET Q f transmit f receive Ф Ф

Tx and RX Tx and Φ

Pulse Width Counter ∆Ф∆Ф Trigger (from microcontroller) CLK (8 MHz) CLK Gate 8 bit counter Microcontroller

Phase Acquisition Distance Computation And Temperature Error Correction A / D Temperature Sensor Read / Write Memory Address Distance Analog Voltage Phase Trigger Pulse SRAM 8 k word x 8 bit Volatile Memory Digitized Voltage PIC16F877 Microcontroller Memory Routine Wait Over Timer A/D Acquisition Time Over Start Microcontroller Clock MUX 2

Microcontroller’s Task Change clock frequency Waits for transducer to settle (30 ms) Sends Trigger pulse to phase comparator Acquires 8-bit phase shifts (  1 and  2 )

Microcontroller’s Task (cont.) Digitizes analog voltage from Temperature Sensor (10 bit A/D) Sends 8-bit phase and Read/Write control signals to external memory

Test Setup

Calculated Vs Actual Distance μ error = 0 σ = 3.4 mm

Calculated Vs Actual Distance μ error = 0 σ error = 3.4 mm

Sources of Error Phase difference jitter  Oscillator drift  Zero-crossing Multipath Effects Component phase shifts Humidity Temperature

Temperature Offset

Current Budget Transmit/Receive: $6.95 Phase Comparator: $2.81 Microcontroller: $5.11 Memory: $3.94 Temperature Sensor: $3.15 Additional Components: $1.35 Budget so far: $23.31

MDR Specifications - Recap “Wireless Ruler” – 1 dimensional static distance measurement Transmit wave between remote and base units (breadboarded) Digital acquisition of raw data SRAM storage of raw data Offline algorithm for distance calculation

CDR Goals Distance calculation on microcontroller Computer link with USB Simultaneous frequency transmission 1-D motion capture (30s) 2-D position and motion Display motion on animation software