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• Monitors heat with IR Thermometer• Listens for relevant cracks with microphone

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 DiagramHeat Coils

Relay 1

Relay 2

Power Supply

Fan

7805 Voltage Rectifier

Rotary EncoderLED

I 2C Bus

Hacrocam Board

Infrared Thermometer

LCD Display

MicrophoneLM386

Pre-Amp

Reset

ATmega 168

Reset PA0 PD5

PD0 PD4PD1-3

PC0 / PC1Vcc

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 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 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 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• 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)

• 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)

• 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 (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)

• 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

Schematic/Theory of Operation: Power Circuit

Schematic/Theory of Operation: Relay Circuits

Schematic/Theory of Operation: LED Circuit

Schematic/Theory of Operation: I2C Circuit

Schematic/Theory of Operation: Microphone/Amplifier Circuit

Schematic/Theory of Operation: Reset Circuit

Schematic/Theory of Operation: Oscillator Circuit

Schematic/Theory of Operation: Microcontroller Decoupling Capacitors

Mic

Power

uC andDigital IO

Analog IO

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

• 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

• 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

• Conversion: 12.6VAC -> ~12VDC -> 5VDC• As with SSR, needs to be relatively isolated• 7805 will need heatsink, so some keepout

area will be neededHeader pins are rated at 1A each, should be

sufficient for power supply

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

Software

• ATMEGA – 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

Basic Software Execution

Project Completion Timeline

Week from now Action Item(s)

1 Proof of Parts/PCB [PCB is done]

2 Software Design Narrative

3 Main microcontroller software

4 Hacrocam controller software

5 Finalize packaging, complete device assembly

6 Thanksgiving

7 Final testing and quality assurance

8 Product presentation and submission

Questions / Discussion