1. Design Constraint TCSP
Team 4
Ethan Price

2. Computation Requirements
Device needs to:
Monitor Microphone PtP
read IR thermometer, >= 2Hz
process camera input (offloaded)
read processed color value
update display
read RPG input
control fan and heater coil
track roasting status, estimate completion time

3. Interface Requirements
Camera, IR thermometer, and display all interfaced through I²C

4. Display Only need to display short phrases, slow refresh acceptable
Software support is preferable
Has to tolerate evelated temperatures, the higher the better
Minimal requirements, cost biggest concern

5. Display Options NHD-C220BiZ by Newhaven Display
2x20 Characters, I2C Interface, 3.3Vdd FSTN (+), WHITE LED backlight 3V, Tranflective, 6:00, Wide Temp, With mounting holes, RoHS
Hitachi HD44780 w/ I2C controller
2x20 Characters, LED backlight
Appears to be a very common display, plenty of sources
"Knock-off" displays incredibly cheap ($2 vs. $10+)

6. Microcontroller
We want to use the Arduino software stack, which uses a Wiring language deriviative targeting Atmel uC's, primarily the ATMEGA series

7. Microcontroller Needs
Minimal processing power
3 analog inputs
I2C
2 PWM
Heat-tolerance
No need for low power versions, heater will use orders of magnitude more power

8. Microcontroller Options
ATmega8A
8KB self-programming flash program memory, 1024-byte SRAM, 512-byte EEPROM, TWI, 6 channel 10-bit A/D converter and JTAG interface for on- chip-debug
One of the smallest ATmega's Atmel recommends for home appliance use
ATtiny2313
2KB ISP flash memory, 128B ISP EEPROM, 128B internal SRAM, universal serial interface (USI), full duplex UART, and debugWIRE for on-chip debugging
Much smaller, it would be tough to work with the SRAM constraint

9. Camera We need a way to monitor the average color of the beans
What we really want is a long range color sensor, giving us the average RGB over a field
Low-resolution camera is an acceptable substitue
Images will need to be captured and processed, requiring a microcontroller with plenty of SRAM
Cameras on uC's are hard.

10. Camera Options HacroCam Make our own "HacroCam"
PCB with VGA camera (640x480), 4Mbit SRAM framebuffer, and controller (AVR XMEGA) chip already mounted, I2C interface
Allows us to offload all of the image processing from our main microcontroller, where the HacroCam creates an average color value over the field and returns a value instead of image data
Make our own "HacroCam"
Still investigating, a few serial-enabled low-res cameras are available, could be combined with another microcontroller and SRAM to make a functional equivalent. Importing this processing into our main uC would be difficult, considering total processing time would be in the .5-2second range.

12. IR Thermometer Needs: good accuracy wide temperature range
narrow field of view
resistant as possible to high heat

13. IR Thermometer Options
MLX90614KSF-ACF
"-70 to 380°C for object temperature
Better than 0.5°C accuracy in the range 0-50°C
0.02°C readout resolution possible"
K - larger temp range
SF - package
B - 5V
C - Temp gradient compensated
F - 10 degree FOV

14. IR Thermometer Options
MLX90616ESF-HCA
Measurement range -70°C to 1030°C
Measurement resolution of 0.02°C
Built in thermal gradient compensation sensor
for fast, stable readings
SMBus compatible digital interface