Reliability and Safety Analysis

Abstract Design and build a compact robot to traverse a maze Use the robot to generate an ASCII representation of the entire maze Mark light locations on map as they are discovered Revisit lights intelligently throughout the maze in a user-defined order

Reliability Analysis PIC18F4550 Microcontroller Model Equation: λP= (C1πT+C2πE)πQπL Parameter nameDescription ValueComments C1Die complexity failure rate.14Based on the MIL-Hdbk-217f [1] for 8 bit microcontrollers πTπT Temperature factor.98Assuming a worst case junction temperature of 85C based on worst operating temp of microcontroller C2Package failure rate Based on equation from MIL-Hnbk-217f page 5-14 [1] for SMT with 44 pins πEπE Environment factor4Handbooks value for mobile devices πQπQ Quality factor10Assumed from the notes that this is the value to use, most likely the value is too large πLπL Learning factor1Number used for devices older than 2 years in production λPλP Failure rate per 10^6 hours MTTFMean Time To Failure Approximately 55 years to a failure for one device

Reliability Analysis Parameter nameDescription ValueComments C1Die complexity failure rate.01Based on the MIL-Hdbk-217f [1] for devices with 100 or less bipolar transistors πTπT Temperature factor58Assuming a worst case junction temperature of 125C based on worst junction temp of the regulator C2Package failure rate.00092Based on equation from MIL-Hnbk-217f page 5-14 [1] for SMT with 3 pins πEπE Environment factor4Handbooks value for mobile devices πQπQ Quality factor10Assumed from the notes that this is the value to use, most likely the value is too large πLπL Learning factor1Number used for devices older than 2 years in production λPλP Failure rate per 10^6 hours MTTFMean Time To Failure Approximately 19.5 years to a failure for one device MIC29150 Low Dropout Regulator Model Equation: λP= (C1πT+C2πE)πQπL

Reliability Analysis Parameter nameDescription ValueComments C1Die complexity failure rate.01Based on the MIL-Hdbk-217f [1] for devices with 100 or less bipolar transistors πTπT Temperature factor58Assuming a worst case junction temperature of 125C based on worst estimated junction temp of the H-bridge C2Package failure rate.0056Based on equation from MIL-Hnbk-217f page 5-14 [1] for SMT with 16 pins πEπE Environment factor4Handbooks value for mobile devices πQπQ Quality factor10Assumed from the notes that this is the value to use, most likely the value is too large πLπL Learning factor1Number used for devices older than 2 years in production λPλP Failure rate per 10^6 hours MTTFMean Time To Failure Approximately 19 years to a failure for one device TI L293 Quadruple Half-H Driver Model Equation: λP= (C1πT+C2πE)πQπL

Reliability Analysis Parameter nameDescription ValueComments λbλb Base failure rate.027Based on the MIL-Hdbk-217f [1] for devices with 20 MHz frequency πQπQ Quality factor2.1Based on devices with a non MIL- SPEC πEπE Environment factor10Handbooks value for mobile devices λPλP Failure rate per 10^6 hours.567 Based on a quartz oscillator calculation MTTFMean Time To Failure Approximately 201 years to a failure for one device CTS CB3 HCMOS/TTL Clock Oscillator Model Equation: λP= λb*πQ*πE

Criticality Analysis 5 Subsection Microcontroller Fuel Gauge User I/O Power Motor contoller

Criticality Levels High Criticality Over discharge of the battery Over heating of components Over charge of battery Erratic movement of robot Low Criticality No power No input/output Does not run

Criticality Analysis – Micro Controller Failure Mode: Output stuck at 1 Possible causes: Overvoltage to the micro Effects: LEDs always off, H-bridge shorted Detection: Observation – Overheated H- Bridge, no LEDs Criticality: High

Criticality Analysis – Fuel Gauge Failure Mode: Reading battery discharging too quickly Possible causes: Rsense shorted, Cf shorted Effects: Misinformation to user about battery state Detection: Observation – Battery indicator drops quickly Criticality - Low

Criticality Analysis – Fuel Gauge

Criticality Analysis – User I/O Failure Mode: User input fails Possible causes: R13/14/15 open Effects: User buttons are floating Detection: Observation – Erratic button presses Criticality - Low

Criticality Analysis – User I/O

Criticality Analysis – Power Failure Mode: 5 V rail > 5V Possible causes: Linear regulator failed Effects: Damage to 5V components Detection: Observation – Regulator too hot, smoke Criticality - High

Criticality Analysis – Motor Control Failure Mode: No output to motors Possible causes: Digital isolators failed, H-bridge failed Effects: Motors will not run Detection: Observation – robot does not move Criticality - Low