DESIGN and DEVELOPMENT of WIRELESS BABY MONITORS Eric
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DESIGN AND DEVELOPMENT OF WIRELESS BABY MONITORS By Eric Yi-Kuo Jen B.A.Sc., Simon Fraser University, 2002 A PROJECT SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ENGINEERING in the School of Engineering Science © Eric Yi-Kuo Jen, 2008 SIMON FRASER UNIVERSITY SUMMER 2008 All rights reserved. This work may not be reproduced in whole or in part, by photocopy or other means, without the permission of the author. SIMON FRASER UNIVERSITY LIBRARY Declaration of Partial Copyright Licence The author, whose copyright is declared on the title page of this work, has granted to Simon Fraser University the right to lend this thesis, project or extended essay to users of the Simon Fraser University Library, and to make partial or single copies only for such users or in response to a request from the library of any other university, or other educational institution, on its own behalf or for one of its users. The author has further granted permission to Simon Fraser University to keep or make a digital copy for use in its circulating collection (currently available to the public at the "Institutional Repository" link of the SFU Library website <www.lib.sfu.ca> at: <http://ir.lib.sfu.ca/handle/1892/112>) and, without changing the content, to translate the thesis/project or extended essays, if technically possible, to any medium or format for the purpose of preservation of the digital work. The author has further agreed that permission for multiple copying of this work for scholarly purposes may be granted by either the author or the Dean of Graduate Studies. It is understood that copying or publication of this work for financial gain shall not be allowed without the author's written permission. Permission for public performance, or limited permission for private scholarly use, of any multimedia materials forming part of this work, may have been granted by the author. This information may be found on the separately catalogued multimedia material and in the signed Partial Copyright Licence. While licensing SFU to permit the above uses, the author retains copyright in the thesis, project or extended essays, including the right to change the work for subsequent purposes, including editing and publishing the work in whole or in part, and licensing other parties, as the author may desire. The original Partial Copyright Licence attesting to these terms, and signed by this author, may be found in the original bound copy of this work, retained in the Simon Fraser University Archive. Simon Fraser University Library Burnaby, BC, Canada Revised: Fall 2007 ABSTRACT The Philips DAP SCD510, SCD520, SCD530, and SCD540 1.8GHz/1.9GHz DECT Digital Wireless Baby Monitors are part of the next generation digital baby monitor products that emphasize on small form factor, innovative feature set, and cost effective bill of materials. New product features include wideband audio, ambient relative humidity measurement, and carbon monoxide detection. The objectives of this project are to design and develop these four baby monitor products and begin mass production for the 1st model within the ten-month time frame. The scope of this project includes baseband hardware design, battery charging algorithm design, and carbon monoxide detection algorithm design. This project report presents the baseband hardware design and implementation, outlines battery charging considerations, describes the battery charging algorithm implementation, examines carbon monoxide detection requirements, and presents the carbon monoxide detection implementation in detail. iii ACKNOWLEDGEMENTS I would like to thank my academic supervisor, Dr. Ash Parameswaran, for his guidance throughout the course of this project. I would also like to thank my technical supervisors, Mr. Eric Ho and Mr. James Tung, for their guidance in the product development and their day-to-day opinions and feedback regarding my work. Their expert opinion and advice was very much appreciated. Moreover, I would like to express my appreciation to all members of the engineering and product development teams at Ascalade Technologies Inc. for their contribution and support during the course of product design and development. Last, and certainly not least, I would like to thank Ascalade Technologies Inc. for the support and founding of this M.Eng project. iv TABLE OF CONTENTS APPROVAL 11 ABSTRACT III ACKNOWLEDGEMENTS IV TABLE OF CONTENTS V LIST OF FIGURES VIII LIST OF TABLES X LIST OF ABBREVIATIONS AND ACRONYMS Xl 1 INTRODUCTION 1 1.1 COMPANY OVERViEW 1 1.2 PROJECT BACKGROUND 2 1.3 PROJECT SCOPE 3 2 DECT WIRELESS BABY MONITOR SYSTEM OVERViEW 5 2.1 PRODUCT FEATURES AND MODEL DESiGNATION 6 2.2 INDUSTRIAL DESIGN 7 2.3 DECTTECHNOLOGY 8 3 BASEBAND HARDWARE DESIGN 11 3.1 BASEBAND HARDWARE DESIGN OF THE BABY UNIT 11 3.1.1 System Controller ASIC 12 3.1.2 Power Management Block 13 3.1.2.1 Adaptor Detection and Adaptor/Battery Switch 16 3.1.2.2 Battery Charging Control Circuit.. 16 3.1.2.3 3.3V Low Drop Out Regulator Circuit 17 3.1.2.4 System Voltage Supplies 18 3.1.3 Audio Processing Block 19 3.1.3.1 Microphone Audio Input.. 21 3.1.3.2 Speaker Audio Output 22 3.1.4 Digital Interface and Control Block 24 3.1.4.1 Crystal Oscillator Circuit and EEPROM 24 v 3.1.4.2 LEDs and LED Driver Circuits 24 3.1.4.3 Keypad Input 25 3.1.4.4 LCD and LCD Driver Circuit 26 3.1.4.5 ATE Debug & Programming Interface 27 3.1.5 Sensor Processing Block 27 3.1.5.1 Temperature Sensing Hardware Implementation 27 3.1.5.2 Relative Humidity Sensing Hardware Implementation 30 3.1.5.3 Carbon Monoxide Sensing Hardware Implementation 31 3.1.6 Radio Block 36 3.2 BASEBAND HARDWARE DESIGN OF THE PARENT UNIT 39 3.2.1 System Controller ASIC 39 3.2.2 Charging Cradle Block 40 3.2.2.1 Charging Indication LED Circuit 41 3.2.2.2 Short Circuit Protection 41 3.2.3 Power Management Block 42 3.2.3.1 Cradle Detection Circuit. 44 3.2.3.2 Li-Ion Battery Charging Circuit 44 3.2.3.3 Battery Current Sense Circuit.. 45 3.2.3.4 System Voltage Supplies 46 3.2.4 Audio Processing Block 47 3.2.5 Digital Interface and Control Block 47 3.2.5.1 Vibration Motor Circuit 48 3.2.5.2 LEDs and LED Driver Circuits 49 3.2.5.3 Keypad Input 50 3.2.6 Radio Block 51 3.3 PHYSICAL IMPLEMENTATION CONSiDERATIONS 51 3.3.1 Integration of RF Circuitry with Baseband Main PCB 53 3.3.2 Utilization of Single 4-Layer Printed Circuit Board 54 3.3.3 Size Reduction of Electrical Components 55 4 BABY UNIT BATTERY CHARGING ALGORITHM 56 4.1 ALGORITHM LIMITATIONS 56 4.2 ALGORITHM DESIGN CONCEPTS 57 4.3 BATTERY TERMINAL VOLTAGE SAMPLING 58 4.4 BATTERY PRESENCE DETECTION 59 vi 4.5 BATTERY CAPACITY COUNTER 60 4.5.1 Initial Battery Capacity Counter Estimation 60 4.5.2 Battery Capacity Counter Update 63 4.6 BATTERY CHARGING CONTROL 64 4.7 AUTOMATIC SYSTEM POWER OFF UNDER Low BATTERy 67 5 CARBON MONOXIDE DETECTION ALGORITHM 68 5.1 CO DETECTION REQUiREMENTS 69 5.2 CO CONCENTRATION MEASUREMENT CALCULATION 69 5.3 CO CONCENTRATION MEASUREMENT CALIBRATION 70 5.3.1 CO Sensor Variation and Resistor Tolerance 71 5.3.2 Amplifier's Non-ideal Characteristics 72 5.3.3 ADC Quantization Error 73 5.3.4 Temperature Dependency 74 5.3.5 Humidity Dependency 75 5.4 CO ALARM CONTROL ALGORITHM 76 6 CONCLUSION 81 7 REFERENCES 83 vii LIST OF FIGURES Figure 1: System Level Block Diagram of DECT Wireless Baby Monitor 5 Figure 2(a): Industrial Design Rendering for SCD510 7 Figure 2(b): Industrial Design Rendering for SCD520 7 Figure 2(c): Industrial Design Rendering for SCD530 8 Figure 2(d): Industrial Design Rendering for SCD540 8 Figure 3: Baby Unit High Level Block Diagram 11 Figure 4: Baby Unit Power Management Schematic Drawing 14 Figure 5: Baby Unit Power Management Scheme 15 Figure 6: Baby Unit Audio Processing Schematic Drawing 20 Figure 7: Baby Unit System Controller Audio CODEC Architecture 22 Figure 8: Baby Unit KBS Switch Matrix 26 Figure 9: Baby Unit Temperature Sensing Circuit. 28 Figure 10: Thermistor Response vs. Ambient Temperature 30 Figure 11: CO Sensor Construction and Reaction Process 32 Figure 12: Baby Unit CO Sensing Circuit 35 Figure 13: Baby Unit Radio Hardware 37 Figure 14: Parent Unit High Level Block Diagram 39 Figure 15: Parent Unit Charging Cradle Schematic 40 Figure 16: Parent Unit Power Management Schematic Drawing 42 Figure 17: Parent Unit Power Management Scheme 43 Figure 18: Parent Unit Vibration Motor Driver Circuit.. 48 viii Figure 19: Parent Unit KBS Switch Matrix 50 Figure 20: Printed Circuit Board Assembly (PCBA) Dimensional Comparison 52 Figure 21: Printed Circuit Board Layout Implementation Comparison 54 Figure 22: Battery Voltage - Battery Capacity Counter Mapping 62 Figure 23: Battery Charging Control Flow Chart 65 Figure 24: CO Detection Implementation Block Diagram 68 Figure 25: Sensor Sensitivity Compensation for Temperature Dependency 75 Figure 26: Calculated CO Alarm Threshold (13) 78 ix LIST OF TABLES Table 1: Main Features of Philips DAP SCD51 0-540 Models 6 Table 2: Parent Unit Dimensional Comparison Between 2007 and 2008 Models51 Table 3: Battery Voltage - Battery Capacity Counter Mapping 62 Table 4: Average Current Charged/Consumed In Different System States 63 Table 5: CO Alarm Conditions Outlined in EN50291 69 Table 6: CO Alarm Conditions Derived from EN50291 76 Table 7: CO Alarm Conditions In Terms OfAccumulative CO Concentration 77 Table 8: Piecewise Linear CO Alarm Threshold (13) 78 x LIST OF ABBREVIATIONS AND ACRONYMS AC Alternating Current ACS Adjustable Current Source ADC Analog to Digital Converter ADPCM Adaptive Differential Pulse Code Modulation ATE Automated Testing