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

Schematic theory of operation oscillator circuit
Schematic/Theory of Operation: Oscillator Circuit

Ece 477 design review team 4 fall 2012

Power Capacitors




uC and

Digital IO

General consideration
General Consideration Capacitors

  • 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 Capacitors

  • 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 Capacitors

  • 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

  • Wavelength@5MHz = ~100meters

  • We're well under 10 meters, not concerned

Pcb layout power supply
PCB Layout: CapacitorsPower 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: CapacitorsMicrocontroller

  • 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

Software Capacitors


    • 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