Homework 11: Reliability and Safety Analysis Team Code Name



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Figure A.3.1: Microcontroller Board Power Supply Circuitry
Figure A.3.2: EOG Board Power Supply Circuitry
Appendix B: FEMCA Worksheet


Failure No.

Failure Mode

Possible Causes

Failure Effects

Method of Detection

Criticality

Remarks

E1

EOG Signal Saturation

R29,R30,C5,C43, All Op-Amp Decoupling Capacitor Short Circuit and Open Circuit

Loss of some EOG commands

Single Eye Gesture No Longer Recognized by the System

Low

This is considered a low level of criticality because it does not completely eliminate EOG functionality




E2

ADS1210 SPI Failure

C42 and C41 Short Circuit; OSC1 Failure

Loss of EOG functionality

Microcontroller Watchdog; Observation

Medium




E3

Unusual Noise Level

Disconnected Analog Ground Electrode; Motion of Signal Electrodes

Inaccurate Analog EOG Signal

Inaccurate EOG Commands

Low





Table B.1: EOG System FMECA Worksheet


Failure No.

Failure Mode

Possible Causes

Failure Effects

Method of Detection

Criticality

Remarks

M1

Failure to Reset

Reset Pushbutton Failure; Switch Debounce IC Failure

Loss of ability to reset microcontroller without resetting the entire system;

Observation

Low

It is assumed that the correct microcontroller program was preinstalled and the reset pushbutton was functional at the time of programming the circuit.



M2

Microcontroller Unresponsive

C2, C3, C4, C5 Short Circuit; C7, C9, C10 short or open circuit; External Oscillator Failure

All subsystems are no longer able to communicate with each other

Single board computer watchdog

Medium




M3

Microcontroller SPI failure

Logic Level Translator Failure; Logic Level Translator Resistors and Capacitors short circuit or open circuit

Loss of communication between EOG and Single Board Computer and microcontroller

Single Board Computer Watchdog; Microcontroller Watchdog

Medium





Table B.2: Microcontroller System FMECA Worksheet


Failure No.

Failure Mode

Possible Causes

Failure Effects

Method of Detection

Criticality

Remarks

P1

Loss of Single Board Computer Power

U25 Input Capacitor Short; U25 Output Capacitor Short; D2 Short; U25 Output Inductor Open Circuit

Loss of Single Board Computer Functionality

Microcontroller Watchdog

High

This is a high level of failure due to the fact that if the single board computer is no longer operational, the user’s sight is blocked.

P2

Loss of Microcontroller Power

SMPS2 Inductor Open Circuit; C30 Open Circuit; R20; C31 Short Circuit; C29 Short Circuit;

Loss of Microcontroller Functionality

Single Board Computer Watchdog

Medium




P3

Loss Of FPGA Power

SMPS1 Inductor Open Circuit; C36 Open Circuit; R22 Open Circuit; C37 Short Circuit; B340 Short

Loss of EOG Signal Analysis

Microcontroller Watchdog

Medium




P4

Loss of +5 EOG Power

C100 Short; C200 Short

Loss of Analog EOG signal

Microcontroller Watchdog; LED1 Indicator

Medium




P5

Loss of -5V EOG Power

C500, polarized input capacitor, output inductor, output polarized capacitor D1 Short Circuit; output inductor, output polarized capacitor D1 Open Circuit;

Complete loss of EOG signal in one direction

User Observation

Low




Table B.3: Power Supply System FMECA Worksheet
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