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

Received Signal

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

Phase Comparator

f

cd

c

fdd

dtπfdAtx

dtπfdAtx

2

211

2

22

2cos)(

22

2cos)(

21

222

22

111

11

Phase Comparatorftransmit

freceive

D

CLK

RESET

Q

D

CLK

RESET

Q

ftransmit

freceive

Ф

Ф

Tx and RX Tx and Φ

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

Test Setup

Calculated Vs Actual Distance

μerror = 0

σ = 3.4 mm

Calculated Vs Actual Distance

μerror = 0

σerror = 3.4 mm

Sources of Error

Phase difference jitterOscillator driftZero-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