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ECE477 Design Review

Team 4 - Fall 2015

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Outline

  • Project overview
  • Project-specific success criteria
  • Block Diagram
  • Component selection rationale
  • Electrical Schematics
  • PCB Layout
  • Packaging design
  • Software design
  • Prototyping progress
  • Project completion timeline
  • Questions / discussion

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Project Overview

  • A wearable technology that can access notifications and displays time and remaining battery whenever user requests
  • Has a reasonable battery life
  • Connects to host device via Bluetooth® technology
  • Utilizes user gestures as inputs to control device

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Project-Specific Success Criteria

  1. Ability to display information, such as phone notifications, weather, and time, on a display and and interact with it
  2. Ability to receive and display notifications from a cell phone via Bluetooth
  3. Ability to recharge an integrated battery
  4. Ability to detect and interact with user through hand gestures (Infrared and accelerometer based)
  5. Ability to customize display to fit a user's personal style

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Block Diagram

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Component Selection:

Microcontroller

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STM32 L1

STM23 L4

STM32 F4

Max Clock speed

32 MHz

80 MHz

168 MHz

Run mode current draw

214 uA/MHz

100 uA/MHz

554 uA/MHz

Standby current draw

0.9 uA

0.42 uA

3.3 uA

Real Time Clock

Yes

Yes

Yes

USART

3

6

4

SPI

2

3

3

I2C

2

3

3

  • STM32L476
  • Familiar
  • Supported by open source tools
  • Popular
  • Best current draw per Mhz

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Component Selection:

Inertial Measurement Unit (IMU)

  • Bosch BNO055 IMU
    • Built in sensor fusion
    • knows exactly where it is in 3D space
    • Runs off 3.3V
  • Shared I2C
  • Other IMUs are more expensive
  • Harder to work with
  • Not as fully featured

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Component Selection:

Bluetooth

  • Prepackaged nRF51822
    • RF is tricky
  • Adafruit Firmware
    • Better than stock
  • Runs off 3.3V
  • Dedicated SPI
  • Could have used a standalone nRF51822 IC and completed the design around that
    • High chance to screw something up

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Component Selection:

Screen

  • UG-2828GDEDF11 OLED screen
  • Integrated SSD1351 display driver
  • Requires between 12V and 18V
  • Dedicated SPI
  • Runs off 13V and 3.3V
  • E-INK
    • Low power draw
    • No color
  • LCD
    • Color
    • High power draw
  • OLED
    • Color
    • Lower power draw (compared to LCD)

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Component Selection:

Gesture Sensor

  • APDS-9960 Gesture Sensor
  • Only sensor of its kind we could find (IR based)
  • Very small
  • Shared I2C
  • Runs off 3.3V

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Component Selection:

Battery Circuitry

  • USB Input
  • MCP73831
    • Battery Charger
  • MAX17948
    • Battery Monitor
    • Reports charge status of battery over I2C
  • 400 mAh Li-ion battery

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Component Selection:

Power Regulation

  • AP2112K-3.3
    • 3.3V LDO
  • FAN5331SX
    • 13V Boost regulator
  • 100 mA current draw, worst case
  • Estimated 4 hour run time, worst case

Part

Current draw in mA

Microcontroller

30 mA

IMU

12 mA

OLED Display

40 mA

Gesture Sensor

0.25 mA

Bluetooth

17 mA

Total

99.25 mA

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Electrical Schematic: Microcontroller

STM32L476

  • Screen - SPI
  • IMU - I2C
  • Gesture Sensor - I2C
  • Bluetooth - SPI
  • Battery Status - I2C
  • Buttons - GPIO

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Electrical Schematic: Microcontroller

  • 8 Mhz Oscillator
  • 32.768 Khz Oscillator
  • USB for charging and uploading code
  • SWD header for programming

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Electrical Schematic: IMU

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Electrical Schematic: Bluetooth

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Electrical Schematic: Screen

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Electrical Schematic: Gesture Sensor

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Electrical Schematic: Power

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Electrical Schematic: Miscellaneous

  • Buttons and pull up resistors
  • Pull up resistors for I2C communications
  • Status LEDs
  • Test Points

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PCB Layout

  • 1.45” x 1.6”
  • Everything on 2 layers

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PCB Layout continued

Top Layer Bottom Layer (Mirrored view)

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Packaging Design

Rendering image with light grey satin finish plastic in SolidWorks 2015

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Packaging Design - Top View

Buttons

Micro USB (Type-B)

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Packaging Design - Watch Strap

  • Designed to fit a standard 22mm NATO watch strap

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Software Design

Initialization

(Power on)

Standby

Clock/Screen Update

(0.5 second interrupt)

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Battery Refresh

Pushbutton | Gesture

Interrupt

Bluetooth Interrupt

State checking

Get Notification

Update Screen buffer

Select

Scroll through options

center button

top/bottom buttons and gesture input

Update settings screen buffer

Low Power Mode

Accelerometer Check

on activity

on low usage

To be started

Currently in Progress

Core Functionality Finished

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Software Design - Current State

  • Displaying time on the OLED screen
    • 0.5 second interrupt is active
  • Graphics library is implemented to draw shapes, bitmap files, and text
  • IMU communication is working
    • Calibration is being worked on
  • Bluetooth module and Gesture sensor have been started
  • Low power states are ready to be implemented

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Software Design - Future

Next steps are to:

  • Create additional pages
  • Receive notification texts from bluetooth module
  • Display notifications on screen
  • Use IMU data to switch back and forth between normal and low power modes
  • Check for push button interrupts
  • Make use of new battery management module to get time remaining and/or percentages
  • Interface with the gesture detection module

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Prototyping Progress

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Project Completion Timeline

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Questions?