Senior Design iiBreathalyzer 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 RequirementsMaximum Operating Temperature: 90CRecommend Operation Temperature: <70CShunt Resistor value: 220-300ohm

Alcohol Sensor Output

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 RequirementsComponent

Max Current Draw (mA)

Recommended Voltage (VDC)

Power Consumption (W)

Display 105 5 0.525

Microcontroller (wireless on)

95 3.3 0.3135

Sensor 650 5 3.25

Charging IC 600 9 5.4

Speaker 60 5 0.3

LEDs, etc 100 9 0.9

Total 1610 -- 10.69

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 +12VDC input

Power Distribution Scheme

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. +9VDC, +5VDC, and +3.3VDC 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.

6.160*850.0

)(60*)(

ADrawAhacityBatteryCap

= 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 overchargedbattery 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: 4.5x2.5x1.5inPhysically Appealing

Resources, Materials and Skill setsPhotoshop SoftwareSolidWorks and/or AutoCAD SoftwareIndustrial Engineering Rapid Prototyping labFabrication material

Enclosure: Contingency Plan

Pactec EnclosuresPPT 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 follows1.0% BAC = 1cg ETOH/mL blood = 9.43 mg ETOH/g blood1ppm = 1 ug ETOH/g blood = 1.06 ug ETOH/mL blood1.06g blood ~ 1mL blood188.6 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

Project Status

Project to date

JANUARY FEBRUARY MARCH APRIL MAY

April 28th, 2010Final Presentation

Hardware Design

Part Acquisition

Received FundingCEI

Testing and Calibration

Assembly

Software Design

PCB Design

HardwareInterface

Final Documentation

Project Budget: $1000