Homework 10

12 Pages·2005·2.06 MB·English

by  Akhil Dharwadkar

ECE 477 Digital Systems Senior Design Project Fall 2005
Homework 10: Reliability and Safety Analysis
Due: Thursday, November 3, at Classtime

Team Code Name: Group 4 VAVA Group No. 4

Team Member Completing This Homework: Akhil Dharwadkar

NOTE: This is the third in a series of four “professional component” homework assignments,

each of which is to be completed by one team member. The completed homework will count

for 10% of the team member’s individual grade. It should be a minimum of five printed pages.

Report Outline:
 Introduction (brief description of design project, with a focus on safety and reliability issues)
 Reliability analysis
o Choose 3-5 components in your design that you believe are most likely to fail (voltage regulators,
power MOSFETs, etc. – basically anything operating above room temperature).
o Perform calculations to determine the number of failures per 106 hours and mean time to failure
(MTTF) for each component, making any reasonable assumptions where necessary.
o Summarize conclusions about the reliability of these components and/or the circuit in general.
 FMECA (failure mode, effects, and criticality analysis) worksheet for entire schematic
o Failure Modes: Divide your schematic into functional blocks (e.g. power circuits, sensor blocks,
microcontroller block). Determine all possible failure conditions of each functional block.
Indicate the components that could possibly be responsible for such a failure (e.g., a shorted
bypass capacitor might cause a voltage drop, but can not cause a voltage increase).
o Effects: For each failure mode above, determine the possible effects, if any, on any major
components in other parts of the design (e.g., damage the microcontroller or fry a resistor) as well
as effects on the overall operation of the project (e.g, audio volume increases to maximum). Do
not waste too much time on this! For some failure modes, it is acceptable to declare the effects
unpredictable. “Method of detection” of a particular failure mode should be observed from the
operation of the device, unless there is particular circuitry intended to detect such a failure.
o Criticality: Begin by defining at least two criticality levels for types of failures in the output of
your design. Define an acceptable failure rate λ for each level of failure. These are up to you and
somewhat arbitrary, but keep in mind λ < 10-9 is standard for any failure that could potentially
injure the user.
 List of references (including MIL-HDBK-217F)

Evaluation:
Component/Criterion Score Multiplier Points
Introduction 0 1 2 3 4 5 6 7 8 9 10 X 1
Reliability Analysis 0 1 2 3 4 5 6 7 8 9 10 X 3
FMECA Worksheet 0 1 2 3 4 5 6 7 8 9 10 X 4
List of References 0 1 2 3 4 5 6 7 8 9 10 X 1
Technical Writing Style 0 1 2 3 4 5 6 7 8 9 10 X 1
TOTAL
Include this sheet as a cover page for your report
ECE 477 Digital Systems Senior Design Project Group 4 VAVA
1.0 Introduction
The “VAVA GPS Data Logger” is a data logging system that logs the latitudinal
and longitudinal co-ordinates of a vehicle’s whereabouts in a timely fashion. There are
two main components – the GPS unit (installed in the back) and the LCD unit (installed
on the dashboard) – that together will also allow the user to see where the car is headed.
The GPS module receives information, which is then processed within the Rabbit
microcontroller. The Rabbit stores one copy of the information in the Atmel Flash
memory, and sends another copy through RF transceivers to the LCD unit, where the
requested information is displayed on a 16x2 LCD module.
The critical reliability and safety issues arise when dealing primarily with
electronics. Since the GPS module is neatly stowed away in the trunk of the car, and the
LCD module is fitted into the dashboard, either module can minimally, if ever, affect the
user physically. The reliability of the data can certainly be questioned due to the choice of
our GPS module. Electronic failures could result in incorrect data logging or could
disrupt the functionality all together.
ECE 477 Digital Systems Senior Design Project Group 4 VAVA
2.0 Reliability Analysis
All electronic components are capable of failure, especially when they function at
above room temperature. However, only a few of the more critical components
will be discussed in the remainder of this report. First, the two microcontrollers –
Rabbit and PIC – will be discussed. Then, the GPS module will be discussed,
followed by the battery charging unit and the step-down converting unit.
The calculation of MTTF will require several assumptions. First, it is
assumed that environmental temperatures would range from 25°C to 40°C.
Secondly, the extreme conditions for particular modules will be used primarily to
get the worst-case analysis. The following constants will be computed over the
rest of this report:
" Part failure rate " Resistance factor
P R
" Application factor " Voltage stress factor
A S
" Base failure rate " Temperature coefficient
! B ! T
" Environmental constant C Die complexity
! E ! 1
" Learning factor C A constant based on the
! L ! 2
" Quality factor number of pins
! Q !

" Power rating factor
! r !

!

!
ECE 477 Digital Systems Senior Design Project Group 4 VAVA
2.1 Rabbit Microcontroller
The Rabbit RCM3300UM Microcontroller is the most important
component in this design. It is responsible for most, if not all, the brainwork in
this system. It is also responsible for running a web server. A failure in the
functionality of the Rabbit could result in the breakdown of the entire design,
as all of the most important data management is carried out in here. The mean
time to failure (MTTF) can be calculated by first determining the probability
of failure in 106 hours of operation. The following equation can be used:
" =(C #$ +C #$ )#$ #$ Failures/106 hours …[EQ-1]
P 1 T 2 E Q L
Table 1: Rabbit Microcontroller MTTF Analysis
Parameter Value Explanation
! The Rabbit 3300 is a 16 bit microprocessor
C 0.28
1
(MIL-HDBK-217F, Section 5.1)
Digital CMOS Device (must not exceed 100°C)
" 1.50
T
(MIL-HDBK-217F, Section 5.8)
! C 0.048 68-pin through-pin device
2
(MIL-HDBK-217F, Section 5.9)
! " 2.00 Assumed Ground Fixed
E (MIL-HDBK-217F, Section 5.10)
! " 10.0 Commercial
Q
(MIL-HDBK-217F, Section 5.10)
! " 1.50 Years in production ~ 1Yr.
L (MIL-HDBK-217F, Section 5.10)
! " 7.7400 Failures per 106 hours
P
!
MTTF ~147 Years

!
2.2 PIC Microcontroller
The PIC Microcontroller is the most important component in the LCD
unit. It receives input from the RF receiver and prints most of the requested
information on the LCD Display. A failure in the PIC Microcontroller could
ECE 477 Digital Systems Senior Design Project Group 4 VAVA
result in the failure of the LCD unit entirely. Although this will not stop the
design from accomplishing its main purpose – data logging – it will however
cutout the user interaction to the LCD unit. The MTTF can be calculated by
first determining the probability of failure, which can be computed using
equation EQ-1.
Table 2: PIC Microcontroller MTTF Analysis
Parameter Value Explanation
The PIC is a 8 bit microprocessor
C 0.14
1 (MIL-HDBK-217F, Section 5.1)
Digital CMOS Device (must not exceed 100°C)
" 1.50
T
(MIL-HDBK-217F, Section 5.8)
! C 0.071 20-pin through-pin device
2 (MIL-HDBK-217F, Section 5.9)
! " 2.00 Assumed Ground Fixed
E (MIL-HDBK-217F, Section 5.10)
! " 10.0 Commercial
Q
(MIL-HDBK-217F, Section 5.10)
! " 1.00 Years in production > 1.5Yr.
L (MIL-HDBK-217F, Section 5.10)
! " 3.5200 Failures per 106 hours
P
!
MTTF ~324 Hours

!
2.3 GPS
The GPS module is responsible for receiving header information and
providing it to the Rabbit Microcontroller. A failure in the GPS module could
also essential shut down all functionality of this design. The GPS unit
provides the sole information that the design runs on. Its MTTF can be
calculated using EQ-1 as well.
Table 3: GPS MTTF Analysis
Parameter Value Explanation
GPS unit has between 101 and 1000 gates
C 0.02
1 (MIL-HDBK-217F, Section 5.1)
1.50 Digital CMOS Device (must not exceed 100°C)
!
ECE 477 Digital Systems Senior Design Project Group 4 VAVA
" 1.50 Digital CMOS Device (must not exceed 100°C)
T
" (8M-pILin- HthDrBoKu-g2h1-7pFin, dSeevcitcioen 5.8)
CT 0.003
2 (MIL-HDBK-217F, Section 5.9)
Assumed Ground Fixed
" 2.00
! E (MIL-HDBK-217F, Section 5.10)
!
! " 10.00 Commercial
Q
(MIL-HDBK-217F, Section 5.10)
! " 1.50 Years in production ~ 1Yr.
L (MIL-HDBK-217F, Section 5.10)
! " 0.5340 Failures per 106 hours
P
! MTTF ~2138 Years

!
2.4 Battery Charger
The Battery Charger is responsible for recharging the battery pack. The
battery pack is to be used when the vehicle is not in use. A failure in the
battery charger could essentially rule out the possibility of running either of
the two units when the vehicle is not in use. This isn’t a major issue, since
logging the data at the last instance the vehicle was used and then logging the
next set of data when the vehicle is used again could easily solve this problem.
The MTTF for the battery charger can be calculated using EQ-1 as well.
Table 4: Battery Charger MTTF Analysis
Parameter Value Explanation
Battery Charging unit has < 100 gates
C 0.01
1 (MIL-HDBK-217F, Section 5.1)
Digital CMOS Device (must not exceed 100C)
" 1.50
T (MIL-HDBK-217F, Section 5.8)
! C 0.0056 16-pin SMT device
2 (MIL-HDBK-217F, Section 5.9)
! " 2.00 Assumed Ground Fixed
E (MIL-HDBK-217F, Section 5.10)
! " 10.00 Commercial
Q
(MIL-HDBK-217F, Section 5.10)
! " 1.50 Years in production ~ 1Yr.
L (MIL-HDBK-217F, Section 5.10)
! " 0.3930 Failures per 106 hours
P
!
!
ECE 477 Digital Systems Senior Design Project Group 4 VAVA
MTTF 2905 Hours

2.5 Step-down Converter
The Step-down Converter is responsible for reducing the input voltage of
7.2V and 5V in the LCD unit and GPS unit respectively to 5V and 3.3V
respectively. A failure in this component could possibly terminate the
functionality of the entire design. The microcontrollers and most of the
circuitry on either of the boards were designed to work on a certain amount of
power. Increasing the amount of power to pins on a microcontroller, for
example, could render the pins useless for further use. The MTTF for this
module can be calculated using EQ-1.
Table 5: Step Down Converter MTTF Analysis
Parameter Value Explanation
Bead Type
" 0.40
B (MIL-HDBK-217F, Section 9.8)
Assume Ground Fixed
" 1.00
E (MIL-HDBK-217F, Section 9.8)
! " 2.00 MIL-SPEC
Q
(MIL-HDBK-217F, Section 9.8)
! " 0.80 Failures per 106 hours
P
! MTTF ~1427 Years

!
3.0 Conclusions
Of all the components, it seems that the Rabbit Controller is most prone to failure:
in about 147 years considering the most strenuous and harshest of conditions. The next
most failure-prone component is the PIC controller, which will fail in about 324 years.
Essentially, these components are very sturdy, and will not fail very soon.
ECE 477 Digital Systems Senior Design Project Group 4 VAVA
4.0 FMECA
4.1 Functional Blocks
The project design is split up into four distinct functional blocks as shown
in figure 1 and figure 2. The labeling of the blocks is as such:
Table 6: Function Block Titling
Letter Functional Block
A Power management
B Controllers/Processing
C Headers/Communication
D Power Supply

Figure 1: GPS Board - Functional Blocks
ECE 477 Digital Systems Senior Design Project Group 4 VAVA

Figure 2: LCD Board - Functional Blocks

4.2 FMECA Worksheet
The criticality in the following table, table 7, is benchmarked on the
following definitions:
1. High : ">10!9
2. Low: 10!9 >">10!12
ECE 477 Digital Systems Senior Design Project Group 4 VAVA

FMECA Worksheet – Group 4

Failure Failure Mode Possible Causes Failure Effects Method of Criticality Remarks
No. Detection
A-1 Output = 0V -Any of the -Data is not Observation Low
components in A logged
could have failed -LCD will not
-improper voltage work
supply
-circuit shorted
A-2 Output > 7.2V -Failure in - Damage to Observation High
(LCD) MAX713A following
Output > 5V modules
(GPS) (MAX1684 and
MAX1831)
A-3 Output > 5V -Failure in MAX1684 Damage to LCD, Observation High
(LCD) PIC, RF Receiver,
RS233 Translator
A-4 Output > 3.3V -Failure in Max1831 Damage to GPS, Observation High
(GPS) RF Transmitter,
Flash Memory
A-5 Battery in not - Bad connection Will not charge Observation/ Low
charging battery testing with
DVM