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Wireless Motion CaptureMid-Year Design Review
Seth BerkowitzDean HowarthEric MarkleinAshesh RastogiAdvisor: 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
8
8
13Free Space
Address
Data
R/W
TriggerPhase Diff
Transmit Transducer
Receive Transducer
Amplifier
Zero-Crossing Detector
BPF
System Block Diagram
Computer Interface
AnalogZero Crossing Comparator
To Phase Comparator
BPF
BW = 377kHz
Transmit transducer
Clock MUX
Receive transducer
Non-Inverting Amplifier
Free Space
Schmitt Trigger Buffer
Recieved Signal Amplitude vs. Transmitted Frequency
0
0.02
0.04
0.06
0.08
0.1
0.12
38.5 39 39.5 40 40.5 41 41.5
Frequency (kHz)
Am
plit
ud
e (
V)
-Transducers 14 cm apart
-3V square pulse wave
Pulse Width Counter∆Ф
Trigger (from microcontroller)
CLK (8 MHz)
CLK Gate
8 bit counter Microcontroller
Phase Acquisition
Distance Computation
And
Temperature Error Correction
A / D8
8
8
8
2
13
10
Temperature Sensor
Read / Write
Memory Address
Distance
Distance
Analog Voltage
Phase
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
TC 10 TC 10
Sources of Error
Phase difference jitterOscillator driftZero-crossing
Multipath Effects Component phase shifts Humidity Temperature
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