Ece 477 design review team 3 spring 2010
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ECE 477 Design Review Team 3 – Spring 2010. Sean Ma. Jacob Champion. Kelli Hacker. George Hadley. Outline. Project overview Project-specific success criteria Block diagram Component selection rationale Packaging design Schematic and theory of operation PCB layout

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ECE 477 Design Review Team 3 – Spring 2010

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Ece 477 design review team 3 spring 2010

ECE 477 Design ReviewTeam 3 – Spring 2010

Sean Ma

Jacob Champion

Kelli Hacker

George Hadley


Outline

Outline

  • Project overview

  • Project-specific success criteria

  • Block diagram

  • Component selection rationale

  • Packaging design

  • Schematic and theory of operation

  • PCB layout

  • Software design/development status

  • Project completion timeline

  • Questions / discussion


Project overview

Project Overview

  • Arm-wearable device for snowsports enthusiasts

  • Provides real-time information: current downhill velocity, temperature, altitude, and airtime - via headphone audio

  • “Emergency mode" uses GPS to navigate the user back to a programmable safe location

  • Li-polymer battery is monitored and recharged in-circuit

  • Target battery life of ten hours

  • Operational in subfreezing temperatures


Project specific success criteria

Project-Specific Success Criteria

  • An ability to communicate sensor data via audio to the user

  • An ability to recharge and monitor an on-board battery

  • An ability to determine current location via GPS

  • An ability to direct the user to a "safe" waypoint

  • An ability to save acquired data to persistent storage


Block diagram

Block Diagram


Component selection rationale

Component Selection Rationale

  • Major components to be selected:

    • Audio Interface

    • Accelerometer

    • Microcontroller

    • GPS Module

    • Altimeter

    • Character LCD


Component selection rationale1

Component Selection Rationale

Audio Interface: VLSI VS-1011e

  • Streaming WAV and MP3 decoder

  • 50 mA active / 30 mA inactive

  • SPI interface (512-byte packets)

  • Headphone driver

Accelerometer: Analog ADXL345

  • 40 uA active draw

  • SPI interface

  • +/-16g maximum

  • Free-fall and motion interrupt support

  • Breakout board available


Component selection rationale2

Component Selection Rationale

Microcontroller: Microchip PIC24FJ256

  • Flexible clock and low power draw

  • Floating-point library support

  • Very few external peripherals needed

  • Large amount of on-chip Flash and remappable pins for flexibility

GPS Module: Polstar PMB-648

  • Excellent fix times

  • Low power consumption and configurable update rates

  • Two-wire TTL serial communication

  • Team members have previous experience


Component selection rationale3

Component Selection Rationale

Altimeter: VTI SCP1000-D01

  • Incredibly low power draw (25 uA at 3.3V)

  • Up to 9 cm resolution in ideal conditions

  • Onboard thermometer saves circuit space

  • Breakout board available

  • SPI interface operation

Character LCD: Newhaven NHD-C0216CiZ

  • Small, light chip-on-glass solution

  • 16 x 2 characters

  • Operates on 3.3V

  • Bright backlight takes only 20 mA


Packaging design

Packaging Design

  • Device needs to be wearable

    • Lightweight

    • Small

  • Device intended to be worn for outdoor sports

    • Durable

  • Package Choice: OKW Ergo-Case

    • Fits above criteria

    • Ergonomic

    • Designed to be worn on the forearm

    • Free Samples

    • Multiple Sizes

    • Armband included


Packaging design1

Packaging Design

LCD

Pushbuttons

DC Power In

Headphone Jack


Ece 477 design review team 3 spring 2010

Schematic/Theory of Operation: Power


Ece 477 design review team 3 spring 2010

Schematic/Theory of Operation: Power

  • 3.3V power rail provided by LTC3440 buck/boost converter

  • On/off slider switch disconnects regulator from circuit

  • Analog comparator prevents battery undervoltage conditions, shutting down regulator at LiPo's minimum 2.75V


Ece 477 design review team 3 spring 2010

Schematic/Theory of Operation: Battery

  • Battery is charged by a 5V wall wart connected to an MCP73811T charge controller

  • 0.1Ω sense resistor provides voltage for LTC4150 fuel gauge

  • Battery voltage connected to uC's ADC for absolute measurement


Schematic theory of operation audio

Schematic/Theory of Operation: Audio

  • VS1011E

  • Decodes MP3 files and drives an audio jack

  • Manufacturer recommended circuit

  • “Native Mode” – recommended for new projects and easier to implement

  • Internal oscillator

  • Separate digital and analog grounds

  • +3.3 V tied to analog and digital VDD

Audio Circuit


Ece 477 design review team 3 spring 2010

Schematic/Theory of Operation: Audio

  • ESD protection at audio jack

  • SPI connection to PIC24

    • SCI for control

    • SDI to receive data

  • xDCS chip select for SDI pulled up – use xCS for both SCI and SDI

  • xReset and DREQ also connected to PIC24

Audio Circuit


Schematic theory of operation accelerometer

Schematic/Theory of Operation:Accelerometer

  • Analog Devices ADXL345 Accelerometer device

  • Utilizes SPI interface (shared with Altimeter module)

  • Useful features: freefall detection, interrupt detection, 13-bit resolution, ±16g range

  • Acceleration data provided used to determine velocity


Schematic theory of operation altimeter

Schematic/Theory of Operation:Altimeter

  • VTI Technologies SCP1000 altimeter device

  • Utilizes SPI interface (shared with Accelerometer module)

  • Useful features: resolution, 18cm accuracy, integrated thermometer

  • Derivative of altimeter data provides Z velocity measurement (used for slope detection, velocity calculations)


Schematic theory of operation gps module

Schematic/Theory of Operation:GPS Module

  • Polstar PMB-648 GPS module

  • Utilizes 2-wire TTL Serial Communication (9600 baud)

  • Useful features: track up to 20 satellites, enhanced performance in canyon/foliage environments

  • Provides XYZ position information as well as time, velocity information used in slope calculations


Schematic theory of operation microcontroller

Schematic/Theory of Operation:Microcontroller

  • PIC24FJ256GA106 microcontroller

  • Central control for Gauntlet device


Schematic theory of operation microcontroller1

Schematic/Theory of Operation:Microcontroller

  • Performs position/velocity/acceleration/time formatting and calculations

  • Displays results to user interface

  • Monitors power supply to check for low-battery conditions

  • External 8 MHz oscillator crystal will be used for increased UART accuracy w/ GPS


Schematic theory of operation microcontroller2

Schematic/Theory of Operation:Microcontroller

Microcontroller Interfaces:

  • UART: 2-wire TTL 9600 baud serial to GPS

  • I2C: 400kHz interface to LCD display

  • GPIO:

    • Battery Monitor

    • Battery Charger

    • Pushbuttons/User Interface

  • SPI (x3):

    • 500kHz for shared accelerometer/altimeter interface

    • 3Mhz interface to MP3 Decoder Chip

    • 4MHz interface to SD Card (subject to change)


Schematic theory of operation storage

Schematic/Theory of Operation: Storage

Will be using a microSD card for memory

Cheap, readily available, persistent memory for prototyping

Can interface with other devices

Smaller than normal SD card, so conserves space

Will use PIC library for FAT32 File I/O system

Connect to microcontroller via SPI bus

No need for pull-ups, according to several sources


Schematic theory of operation user interface

Schematic/Theory of Operation: User Interface

  • User Input:

    • Pushbuttons (Use Generic I/O)

    • Menu System

  • Audio:

    • The VS1101E MP3 Decoder has built-in audio driver

    • Communicates with microcontroller using SPI

  • LCD:

    • Character LCD

    • Communicates via I2C


Ece 477 design review team 3 spring 2010

PCB Layout


Ece 477 design review team 3 spring 2010

PCB Layout: Power

  • Buck-boost circuit layout is crucial to proper performance

  • Inductor traces must be wide to support high current

  • Must be isolated from other digital circuitry


Ece 477 design review team 3 spring 2010

PCB Layout: Battery

  • PCB must act as heatsink for linear charge regulator

  • Sense resistor should be as close to fuel gauge as possible

  • Power traces should be kept wide and short for minimal losses


Pcb layout audio

PCB Layout: Audio

  • Analog and digital ground need to be tied close to VS1011E

  • Decoupling capacitors placed as near as possible

  • Header connection for SPI and microcontroller signals

  • Audio jack must be on right edge of PCB for user access


Pcb layout sensors

PCB Layout: Sensors

  • Accelerometer must be by mounting point to avoid circuit resonance

  • Breakout boards for accelerometer and altimeter placed on edge of circuit to conserve space

  • Accelerometer and altimeter placed close to one another – share an SPI bus

  • Header for ribbon cable to GPS

  • Header for access to SPI bus and chip selects


Pcb layout microcontroller

PCB Layout: Microcontroller

  • 64-pin QFP package

  • Contains 3 digital power/ground pairs, 1 analog power/ground pair, Vddcore and Vddcap pins

  • Require .01µF decoupling capacitors (locate near microcontroller)

  • Requires 8MHz external crystal (locate near MCU)


Software design development status

Software Design/Development Status

  • Components verified for correct functionality

  • Primarily timer-based – allows for low power consumption

  • At set intervals:

    • Poll accelerometer for jump data

    • Poll GPS and altimeter for velocity and position

    • Poll altimeter for temperature

    • Poll battery for absolute voltage

    • Poll pushbuttons for user input

  • Act on readings by

    • Calculating downhill velocity

    • Notifying user via audio (user-set intervals)

    • Saving GPS/altitude waypoints as needed

    • Activating modes of operation based on user input


Project completion timeline

Project Completion Timeline


Questions

Questions?


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