ece 477 design review team 4 fall 2012
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ECE 477 Design Review Team 4  Fall 2012

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ECE 477 Design Review Team 4  Fall 2012. Paste a photo of team members here, annotated with names of team members . Project Overview. Automated Coffee Roaster Popcorn popper Includes heating elements and fan Automatic roasting added User interface Optically tracks bean color

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ece 477 design review team 4 fall 2012

ECE 477 Design Review Team 4  Fall 2012

Paste a photo of team members here, annotated with names of team members.

project overview
Project Overview
  • Automated Coffee Roaster
    • Popcorn popper
      • Includes heating elements and fan
    • Automatic roasting added
      • User interface
      • Optically tracks bean color
      • Monitors heat with IR Thermometer
      • Listens for relevant cracks with microphone
project specific success criteria
Project-Specific Success Criteria
  • An ability to achieve different levels of roasting based on user input
  • An ability to detect the temperature of the beans
  • An ability to monitor the color of the beans
  • An ability to interact with the user through a GUI
  • An ability to shut off the device if unusual conditions (high temperatures, unusual color, abnormally long time) are detected
block diagram

Heat Coils

Power Supply


Relay 1

Relay 2

7805 Voltage Rectifier




ATmega 168



Rotary Encoder





PC0 / PC1




I2C Bus

Hacrocam Board

Infrared Thermometer

LCD Display

Block Diagram
component selection rationale
Component Selection Rationale
  • ATmega 168
    • Atmel recommended for home appliances
    • 16KB self-programming flash program memory
    • 512-byte EEPROM
    • Compatible with Arduino software stack
  • Hacrocam
    • Open source
    • Mounted microcontroller that is also compatible with Arduino software stack
component selection rationale1
Component Selection Rationale
  • IR Thermometer (MLX90614KSF-ACF)
    • -70°C – 380°C detection range
    • 10 degree field of view, trig verified
    • Compensated temperature gradient
  • LCD Display (NHD-C220BiZ)
    • Simple communication method
    • Transflective
    • Resists wide temperature range
component selection rationale2
Component Selection Rationale
  • Microphone
    • Highly directional
    • Very cheap
  • LED
    • White light to not bias color
    • Lid will be covered with high-heat spray and aluminum to isolate light
component selection rationale3
Component Selection Rationale
  • AC Relays (Heating Coils)
    • 240 V @ 12 A (only need 10A)
    • Fast switching (40 ms transition)
    • Activation voltage of minimum 4V
    • Solid State
  • DC Relay (Fan)
    • 30 V @ 2A
    • Solid State
packaging design
Packaging Design
  • As simple as possible, but homely
  • External build quality of the Nesco product
  • Operational similarity, simplicity, and homely of Engadget product
  • More functionality than both, better component placement
  • Minimal exterior components
theory of operation heat dissipation
Theory of Operation (Heat Dissipation)
  • All components are high heat rated
  • Camera will be behind acrylic heat shield
  • Microphone will have metal mesh windscreen
  • All electronics besides sensors will be below heating chamber
  • Fans and ventilation ducts will further cool all electronics
theory of operation power
Theory of Operation (Power)
  • Wall voltage will run the heating coils directly
  • Wall voltage will be transformed to 25.2 VAC and then rectified to run the fan.
  • Also transformed to 12.6 VAC, rectified, and sent through a 7805 voltage regulator to power the microcontroller at 5V
theory of operation i 2 c
Theory of Operation (I2C)
  • Two microcontrollers
  • The Hacrocam, IR Thermometer, and LCD screen will be accessed via I2C bus.
  • Hacrocam will use self-mounted micro to average picture color before sending data.
  • Base microcontroller will track and average the last 2-3 IR temperature readings.
  • LCD screen will be used to communicate with the user.
theory of operation user interaction
Theory of Operation (User Interaction)
  • Rotary encoder will allow the user to scroll through and select roasting options
  • Reset will allow the user to cancel the roasting at any time
  • Microphone will establish a “noise floor” to monitor base number of peaks in the area
    • Will listen to number of peaks for every other half second to determine if the beans are cracking





uC and

Digital IO

general consideration
General Consideration
  • Acid Traps, no acute angles
  • Signal Bounce, no right angles
  • Signals in different layers should pass perpendicularly if possible
  • Analog and Digital need separate grounds (star routing)
  • Ground Fill in real PCB
pcb layout solid state relays
PCB Layout: Solid State Relays
  • Control signals need minimal amounts of current: ~30mA. Standard 10mil trace will suffice
  • SSR1: Mounted on the PCB, will have to pass 1.7A of 20VDC for the fan. This will need to have >50mil traces and molex connectors, plus etxra space between traces
  • SSR2: Mounted separately from PCB
pcb layout i2c
PCB Layout: I2C
  • 100KHz operation; noise, impedance, and signal length possible concerns (rated to ~1m)
  • Rule of thumb: <1/10 of wavelength, transmission line effects not a concern
  • I2C fall time is about 100ns = 5MHz
  • [email protected] = ~100meters
  • We\'re well under 10 meters, not concerned
pcb layout power supply
PCB Layout: Power Supply
  • Conversion: 12.6VAC -> ~12VDC -> 5VDC
  • As with SSR, needs to be relatively isolated
  • 7805 will need heatsink, so some keepout area will be needed

Header pins are rated at 1A each, should be sufficient for power supply

pcb layout microcontroller
PCB Layout: Microcontroller
  • All voltage pairs have decoupling caps, need to be placed nearby
  • Want to attempt to keep uC and headers away from switching noise of amplifier and transistors
  • Crystal and associated caps are slammed up against the microcontroller
    • Arduino software stack
      • Open-source, higher level Processing language
      • Included libraries for I2C
  • Hacrocam
    • Interfaces with Arduino Software
    • Programmable through serial interface
    • Extra SRAM for additional processing routines
      • Color averaging done on-chip