Team 4: Shicheng Guo, Kyle Haver, Ethan Price, Wesley Tso

  Device that automatically roasts coffee beans based on a roast level selected by user via GUI.  Device uses base popcorn popper, as well as a variety of sensors, to achieve automation.  Safety is a major concern due to high power usage and heat generated by device being the main possible causes of critical failures. Overview

  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 via GUI  An ability to shut off the device if unusual conditions (dangerously high temperatures, unusual color in roasting area, or timeout) are detected. PSSCs

  Components listed in order of “closeness” to power and heat of device.  AC Relay (ST24D12): controls heating coil.  DC Relay (LCA717S): controls cooling fans and rotates beans.  Microprocessor (ATMEGA8A-AU): controls overall operation, including the relays and safety checks.  Voltage Regulator (LM7805CT): regulates power to microprocessor, therefore indirectly affecting relays.  Transformer ( ): supplies power to microprocessor circuit, including voltage regulator, relays, voltage regulator, and microprocessor. Components Chosen

  λ p = λ b * π Q * π E Failures/10^6 hours.  λ p = 1.6 Failures/10^6 hours. AC Relay Parameter nameDescription ValueComments λbλb Base Failure Rate0.40Solid state without time relay πQπQ Quality Factor4.0Commercial spec. πEπE Environment Factor1.0For use in homes, which are not mobile have temperatures are within human tolerances.

  λ p = λ b * π Q * π E Failures/10^6 hours.  λ p = 1.6 Failures/10^6 hours. DC Relay Parameter nameDescription ValueComments λbλb Base Failure Rate0.40Solid state without time relay πQπQ Quality Factor4.0Commercial spec. πEπE Environment Factor1.0For use in homes, which are not mobile have temperatures are within human tolerances.

  λ p = (C1 * π T + C2 * π E) * xQ * xL Failures/10^6 hours.  λ p = Failures/10^6 hours. Microprocessor Parameter nameDescription ValueComments C1Die Complexity Failure Rate0.148 bit Microprocessor. πTπT Temperature Factor 0.96No mention of junction temperature in datasheet; used 85C maximum temperature for overall device. C2Package Failure Rate.013DIP with under 36 pins, soldered. πEπEEnvironmental Factor 0.5For use in homes, which are not mobile have temperatures are within human tolerances. xQQuality Factor2.0Basic quality compliance. xLLearning Factor1.0Has been in production for > 2 years.

  λ p = λ b * π T * π S * π C * π Q * π E Failures/10^6 hours.  λ p = Failures/10^6 hours. Voltage Regulator Parameter nameDescription ValueComments λbλb Base Failure Rate0.0020Default value for all voltage regulators. πTπT Temperature Factor5.1 Max junction temperature of 125C. πS πS Electrical Stress Factor1.0Default value for all voltage regulators. πCπC Contact Construction Factor1.0Metallurgically Bonded contacts πQπQ Quality Factor2.4Lowest quality factor for discrete semiconductors. πE πE Environment Factor1.0For use in homes, which are not mobile have temperatures are within human tolerances.

  λ p = λ b * π Q * π E Failures/10^6 hours.  λ p = Failures/10^6 hours. Transformer Parameter nameDescription ValueComments λbλb Base Failure Rate0.019No operating temperature found, as this is a generic transformer from Radio Shack with no data sheet. Used conservatice 100C max rating with second weakest insulation class. πQπQ Quality Factor30Is a power transformer, commercial spec. πEπE Environment Factor1.0For use in homes, which are not mobile have temperatures are within human tolerances.

  Sensors (Microphone, Camera, Thermometer)  Rotary Encoder  LED  Display Other Components

  Most prone to critical failures are the relays.  Possible design alternatives:  Have two relays ORed together for each current relay. For AC Relay, OR for off functionality. For DC relay, OR for on functionality.  Spend way more money on higher grade relays.  Neither are very appealing. Summary

  AC Relay Data Sheet:  DC Relay Data Sheet: df/$file/LCA717.pdf df/$file/LCA717.pdf  Microprocessor Web Link:  Voltage Regulator Data Sheet:  Transformer Web Link: Id= Id= Links