Senior Design ii

canolaokahumpkaElectronics - Devices

Nov 2, 2013 (3 years and 5 months ago)

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Senior Design ii

Breathalyzer Interlock system

By: Xi Guo | Ashish Thomas | Brandon Gilzean | Clinton Thomas

Project Description


A system to designed to deter individuals from operating a
motor vehicle while under the influence of alcohol.


Highly accurate and portable alcohol sensing unit allows the
operator to monitor their level of intoxication while away from
the motor vehicle


Integrated automobile control unit prevents the vehicle from
operating without a successful initial reading, then conducts
rolling retests to verify driver sobriety during vehicle operation


Logs of activity maintained by automobile unit for retrieval
during calibration by law enforcement.

Motivation and Goals


Original concept was personal alcohol measurement device
powered by a smartphone (iPhone, Android, etc.)


Platform and Business considerations lead to the determination
to make a standalone device


Evaluation of work quantity lead to the marriage of alcohol
detection device with automobile interlock unit


Goal is to develop a system that can meet National Highway
Safety and Transportation Agency certification for alcohol
detection interlock devices.

Trade Study


Breathalyzers


Personal breathalyzers utilize silicon
dioxide based ethanol sensors,
reducing both cost and accuracy


Unique air channel design that folds
into the case enclosure. This will be
modeled or acquired for Voog


Simple means of communication
using speaker and 2
-
Digit 7
-
Segment
display


Small and lightweight, powered by
non
-
rechargeable AA alkaline
batteries

Trade Study


Ignition Interlock


Smart Start Model 20
-
20
evaluated as the most effective
and complete solution currently
available


Typical Interlocks utilize a “zero
-
tolerance” policy, meaning
interlock engages between 0.02
-
0.04% BAC


No available model in the market
can completely prevent
spoofing, only deter and catch
for later retrieval

Project Overview


Hand
-
Held Unit


Handles user interaction
and processes sensory data


Powered by onboard Li
-
ion
battery


Wireless Communication
with automobile control unit


Control Box


Requests validation from
handheld unit


Establishes vehicle state,
logs input data

System Logic & Displays


Introduction to System Logic


FPGA vs. Microcontroller


Microcontroller


PIC18F, Texas Instrument MSP430



Display


Seven
-
Segment Display, Dot
-
Matrix Display,
Liquid Crystal Display

Introduction System Logic


The system level design for both the handheld
breathalyzer unit, as well as the automobile control unit,
calls for the use of programmable logic.



This is necessary for the successful interpretation of output
signals from the sensors, translating user input into device
functionality, displaying information related to the current
state of the device, as well as communication with other
devices in the system.


Field
-
Programmable Gate Array


Integrated
-
circuit designed to be programmed
after it has been manufactured


Advantages


Using languages such as VHDL and Verilog
you can create complex logic structures.


FPGA is extremely flexible (implement
processors, multipliers, network protocols)


Disadvantages


More complex to program than
microcontroller


Power Consumption






Microcontroller


Small computer on a singleintegrated
circuit

consisting internally of a relatively simple
CPU,

clock,

timers, I/O ports, and memory.


Advantages


Using languages such as C/C++ Assembly


Low cost


Disadvantages


Have to design a microcontroller into a circuit
and build it


Paying for functionality that is not being used





Microcontroller


Memory


Data storage, Computation…etc


Communication


RS232, USB…etc


Wireless Capabilities


Ability to transmit and receive data

Microcontroller (PIC18F)


PIC18F


10
-
bit Analog
-
to
-
Digital Converter


Two Capture/Compare/PWM (CCP) modules.


3
-
wire SPI™ (supports all 4 SPI modes)


I2C Master and Slave mode


Low power


USB V2.0 Compliant


Memory 32 Kbytes

Microcontroller (MSP430)


Texas Instrument MSP430F2274


Low voltage power supply
requirements (1.8 VDC


3.6 VDC)


Universal Serial Interface,
configurable as either I2C, SPI, or
UART for RS232 serial
communications


Available Analog
-
to
-
Digital
converters with 10/12/16 bits of
resolution


Assembly or C/C++


Memory 32Kbytes Flash, 1Kbytes
RAM




Microcontroller (MSP430)

Display


Human Interface


Seven
-
Segment Display


Arabic numerals 0 to 9


General use


Dot
-
Matrix Display


Simple display limited resolution


Liquid Crystal Display


Great for character resolution


Refresh Rate

LCD Display
-

LCD0821


RS
-
232/TTL and I2C
protocols


Communication speeds,
up to 57.6 kbps for RS
-
232
and 400 kbps for I2C


extreme environments of
-
20C to 70C

Sensors


Alcohol Gas Sensor


Semi
-
Conductor (MQ
-
3) vs.
Fuel Cell (002
-
MS3)


Differential Pressure Sensor


Silicon Microstructures (SM
-
5852)

MQ
-
3

MS3

Alcohol Sensor

Operating Condition
and Requirements


Maximum Operating
Temperature: 90C


Recommend Operation
Temperature: <70C


Shunt Resistor value: 220
-
300ohm

Alcohol Sensor Output

0
100
200
300
400
500
600
700
800
900
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
0.11
0.12
0.13
0.14
0.15
0.16
Test 1
Test 2
Test 3
Testing Condition


Room Temperature


0.5ml gas sample


0.160 BAC

Region of Interest

<0.04 BAC (User will not
be able to start the
vehicle)

Alcohol Sensor Calibration


Sensor Output will be calibrated
against known values using Lifeloc
Dry Gas Calibration Kit


Typically, dry gas alcohol calibration
requires a 5
-
6% compensation value
to approximate breath alcohol


Values will be measured using a
laboratory
-
formulated alcohol
standard of particular
concentration, representing BAC
values of 0.02 to 0.10

Differential Pressure Sensor


Object: To detect sufficient breath sample has
been provided.


Option A: Tungsten Hot wire Anemometer


Electrical Resistance varies with the change in
temperature due to breath sample


Cons: Can’t detect the quantity of breath sample
obtained. Expensive. Not available as discrete
solution


Option B: SI
-
Micro Pressure Sensor


Pressure detection range: 0.15
-
3 Psi (Human breath
sample (1.5 to 2.5 Psi)


Cons: Difficult to obtain from chosen manufacturer,

difficult to mount.

Differential Pressure Sensor

Power Supply


How to power


Ability to hardwire into vehicle’s electrical system (in
-
car unit)


Recharge on
-
board battery with same circuit board
(portable unit)


Utilize external “wall wart” to recharge battery, or cigarette
lighter connection (portable unit). So 12V primary input.


Various power needs of components in both units will require
a power supply with multiple capabilities


Power Requirements

Component

Max Current Draw
(mA)

Recommended Voltage (V
DC
)

Display

105

5

Microcontroller
(wireless on)

95

3.3

Sensor

650

5

Charging IC

600

9

Speaker

60

5

LEDs, etc

100

9

Total

1610

--

Power Requirements (contd)


While maximum draw possible is ~1.6A, it is at various
voltages and not all will be drawing at the same time for
a significant period of time


Multiple voltages are needed for multiple components.
Therefore, will utilize voltage regulation to generate
multiple output voltages from singular +12V
DC

input

Power Distribution Scheme

+12V I n

+9V Out

Charging
Circuit

Battery
(+7.4V)

+5V Out

Display

Sensor

Speaker

LEDs

+3.3V
Out

Microcontroller
&Wireless Radio

Portable Unit

Control Unit

Implementing Power Scheme


For our application, voltage dividers do not offer voltage
stabilization, and are fairly inefficient. They also lack any sort
of basic power protection (short circuit, overcurrent,
overvoltage, thermal overload, etc.).


Zener diodes allow a stable output voltage; but again, lack
more robust power event protection.


Use LDO voltage regulator ICs. Switching regulators were
considered, but due to their buggy reputations, were not
used. They also take up slightly more space on the PCB land
configuration due to a need for a larger (compared to LDO)
supporting circuit. Heatsinking will be used as needed.
+9V
DC
, +5V
DC
, and +3.3V
DC

are needed.

Battery


Portable unit needed to be portable,
but also not impractical to use by
having to replace disposable
batteries. Since highest regulator to
be served by battery is 5V, a 7.4V
battery should suffice.


Load and current draw expectations
made conventional alkalines
impractical.


Due to size, energy density, as well as
flexibility in recharging, lithium ion
rechargeable batteries were chosen.

7.4V 850
mAh

Li
-
Ion Battery
with Integral Protection PCB.
>1C safe discharge rate.

= 31.875 minutes

Expected Battery Runtime?

Charging the Battery


However, a charging
circuit is now required.
Lithium ion batteries
require more care in
charging, as improper
charging can result in
a fire or explosion


not desirable for any
user, especially an
inebriated user


Circuit to right. Will be
a two cell battery
(3.7V*2 = 7.4V)

Reprinted with Permission of shdesigns.org

Charging the Battery (contd)


However, the area required

on the PCB for this configuration

is too great; it also is not intelligent.

It cannot automatically detect a

severely discharged or overcharged

battery and cannot switch

charging modes to compensate.


Use Texas Instruments BQ24005. A complete, integrated
charging IC for use with two cell LiIon and LiPoly
batteries


Heat issues are addressed by soldering a thermal pad
on the bottom of IC to a copper pad in the PCB


the
PCB becomes a heatsink.

Jumper

Portable Unit Config

Base Unit Config

J1

Closed

Open

J2

Open

Closed

J3

Closed

Open


To allow usage of same
board for both fixed and
portable power application,
a set of three jumpers can
be adjusted to allow for
either configuration.

Physical Implementation


Since small size, reliability, and quality are all primary
concerns of our overall project, we decided to use a
PCB.


PCB Requirements:


Compact: 2 in. x 3 in. (6 in.
2

total area). This is slightly smaller
than an average credit card.


Must accommodate microcontroller board within PCB area


Design so a single board can be used for both portable and
base/control units


Design for optimal power flow, and minimize capacitive,
inductive, and other crosstalk effects from traces, especially
between analog and digital I/O lines.

Physical Implementation (contd)


Design considerations:


32 mil for width of power traces


15 mil for width of signal traces


25 mil minimum for signal trace spacing


Mostly dedicated ground plane for robust ground


Two layer to save on cost.


All outputs should have standard 0.1 in. spacing (2.54 mm) to
accommodate standard pin headers. This will mostly avoid
the need to solder components directly to the board, easing
debugging and future changes.


Wide traces to small pads on the charging IC should be
necked near pad interface


PCB Manufacturer Choice


Used PCB123.com (Sunstone
Circuits)


Used PCB123 PCB layout and
schematic editor software


With silkscreen on top only, 1 oz
copper thickness, soldermask, and
our 6 sq. in., the per board price is
$32.48 for 8 boards. ($32.48 * 8 =
$259.80)


Lead time of three business days
when order is submitted before 12
PM PST

Enclosure:
Hand
-
held & Control box

Requirements (Hand
-
held unit)


Dimensions: 4.5x2.5x1.5in


Physically Appealing


Resources, Materials and Skill sets


Photoshop Software


SolidWorks and/or AutoCAD Software


Industrial Engineering Rapid
Prototyping lab


Fabrication material

Enclosure:
Contingency Plan

Pactec Enclosures

PPT 3468



Signal Acquisition


Alcohol Concentration will be determined using a “Peak
Measurement” method


Output measured over small load resistor (220


390 ohms)


Voltage is converted into discrete 10
-
bit integer representation
by ADC with internal 1.5V reference


Output represents the maximum alcohol concentration
detected by the sensor in micrograms.


Airflow pressure will be queried from the differential sensor
utilizing I2C, returned from the sensor’s onboard DSP.

BAC Measurement


Micrograms of alcohol is converted to BAC using the Blood/Breath
Partition Ratio, 2300:1 US, 2100:1 UK


Assumption is made that test is
post
-
absorbitive
, meaning the alcohol is
fully absorbed and in bodily equilibrium


Approximate values are as follows

1.0% BAC = 1cg ETOH/mL blood = 9.43 mg ETOH/g blood

1ppm = 1 ug ETOH/g blood = 1.06 ug ETOH/mL blood

1.06g blood ~ 1mL blood

188.6 ug/mL


377.2 ug/mL is blood concentration for 0.02
-
0.04%

82 ng/mL


164 ng/mL will be range of BrAC


Assumptions of flow rate will be evaluated during assembly and
calibration to determine breath sample quantity



Software Development


Software will be written using
IAR Embedded Workbench


Kickstart version for MSP430
provided by TI limits program
size to 4K. Full version does
not have this limit, but costs
lots of $$$


Software will be written in C,
with inline assembly for
MSP430 where needed

Software > Hardware… always


What happens when you find out after purchasing your
hardware that it cannot achieve all the functionality you
believed it could?


MSP430F2274 provides a universal serial UART for I2C, SPI, RS232,
etc., which just so happens to be used by the CC2500
transceiver


Communications with peripheral devices and sensors will be
accomplished through an I2C serial bus


Luckily for us, the right combination of configurable GPIO pins
and software can save our project, utilizing a technique called
“Bit
-
Banging”

What is Bit
-
Banging?


A technique used for serial communications utilizing software
instead of dedicated hardware


Software sets and samples the state of pins on the
microcontroller, responsible for timing, signal levels,
synchronization, etc.


Can reduce costs in a design by implementing features that
are not designed directly into the hardware (or make up for a
lack of foresight)



Considered a hack, takes more CPU time and resource, signal
is usually much uglier than dedicated hardware would
provide

Inter
-
Integrated Circuit (I2C)


Daisy
-
chained serial peripheral bus designed for simple slave
-
to
-
master device communications


Only requires two lines, SCL (clock) and SDA (data)


Each device is given an address on the bus, configured by
software


Communications initiated with START and STOP messages


First byte is the address of the device the master will
communicate with, then the desired direction of
communication (write/read), followed by an ACK from the slave
device

Inter
-
Integrated Circuit (I2C)


Each byte is followed by a
START message until
desired end of
transmission, which is
indicated with a STOP
message

System Diagram

Software


State Transition


Hand Held Unit (Passive Device)


Wait State


Processing input from user


Processing State


Receiving and processing sensor data



Display State/Transfer


Display to LCD,


Control Box Unit (Active Device)


Wait State


Receive wireless transmission


Functional States


Enable, disable, and alert state.



Idle State


Counting down to the rolling retest.

Transition State Diagram

Hand Held Unit Control Box Unit

Block Diagrams

Control Box Unit Hand Held Unit

Interlock and Demo Setup


The interlock will prevent the vehicle from starting if the
user’s BAC is deemed to be too high.


Will do this by routing the fuel pump’s power through a
relay; this will prevent starting whether the starter or
clutch (bump start) is used to start the car


Signal from microcontroller will control the relay, which
will switch the higher amperage fuel pump power.
Protection diode will be used across relay.


For our demonstration, will use an RC car, as no actual
vehicle is available for demo purposes

Interlock and Demo Setup
(contd)

Work Distribution

X. Guo

A.
Thomas

B.

Gilzean

C. Thomas

Case Enclosure

Power Delivery

Control

Software

Utiliity

Software

Sensor
Selection

Charging
Circuit

Communicatio
ns (wireless)

Communicatio
ns (peripheral)

Layout and
Design

PCB Layout
and Design

Regression
Testing

PCB Layout
and Design

Project Status

Project to date

JANUARY

FEBRUARY

MARCH

APRIL

MAY

April 28
th
, 2010

Final Presentation

Hardware Design

Part Acquisition

Received Funding

CEI

Testing and
Calibration

Assembly

Software Design

PCB Design

Hardware

Interface

Final Documentation

Project Budget: $1000

Item

Cost

Spent

PCB

$32.48 (8)

$260

Differential Pressure Sensor

$0.00

RC Car

$40

$40

Battery & Charger

$45

$45

Enclosures

$15

$15

12V Relay

$3 (2)

$6

Alcohol Sensor

$24.15(2)

$25

Voltage Regulator

$
1.50 (10)

$15

Speakers and Buzzers

$10 (2)

$20

Dry Alcohol Standard Test

$325

$0.00

Total

$750.84

$425.84