Alcohol Gas Detector

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i



Alcohol Gas
Detector


Breathalyzer




Prepared for Electronics Engineering Technology Staff











By Sean Enright

May 26, 2011

ii



Alcohol Detector

Project





Produced for:

Steve Adamson

NBCC Saint John Instructor



Submitted by:

Sean Enright

Electronics Engineering Student

506
-
650
-
3611











iii



Table of Contents

Table of Figures

................................
................................
................................
................................
.
iv

Summary

................................
................................
................................
................................
...........
v

1.0 Introduction
................................
................................
................................
................................
..
1

1.1 Overvi
ew

................................
................................
................................
................................
..
1

1.2 Basic Design and Operation
................................
................................
................................
........
1

2.0 Main Components
................................
................................
................................
.........................
2

2.1 MQ
-
3 A
lcohol Sensor

................................
................................
................................
.................
2

2.1.1 MQ
-
3 Operation
................................
................................
................................
..................
3

2.2 MQ Carrier Board

................................
................................
................................
......................
4

2.3 Parallax SumoBot Circuit Board

................................
................................
................................
..
5

3.0 Design and Construction
................................
................................
................................
................
6

3.1 Sensor Circuitry

................................
................................
................................
.........................
6

3.1.1 Voltage Divider

................................
................................
................................
...................
7

3.2 Display Circuitry

................................
................................
................................
........................
8

4.0 Gas Analyzer Operation

................................
................................
................................
.................
9

4.1 Explanation

................................
................................
................................
...............................
9

4.2 Calibration

................................
................................
................................
..............................

10

4.2.1 Test Data

................................
................................
................................
..........................

11

5.0 Information

................................
................................
................................
................................

12

5.1 Time Frame
................................
................................
................................
.............................

12

5.2 Budget and

Part List

................................
................................
................................
................

12

6.0 Conclusion and Recommendations
................................
................................
...............................

13

References Cited

................................
................................
................................
..............................

14

APPENDEX
................................
................................
................................
................................
........

15

Basic Stamp Code Flowchart

................................
................................
................................
..........

16

Ba
sic Stamp Source Code

................................
................................
................................
..............

17

MQ
-
3 Sensor Data Sheet

................................
................................
................................
...............

19



iv



Table
of

Figures


Figure 1 MQ
-
3
Sensor

................................
................................
................................
.........................
2

Figure 2 MQ
-
3 Contacts

................................
................................
................................
......................
3

Figure 3 Heating Tube

................................
................................
................................
.........................
4

Figure 4

MQ Sensor Board
................................
................................
................................
...................
4

Figure 5 SumoBot
Board

................................
................................
................................
.....................
5

Figure 6 Se
nsor Circuitry

................................
................................
................................
.....................
6

Figure
7 Volt Divider

................................
................................
................................
...........................
7

Figure 8 Di
splay Circuitry
................................
................................
................................
.....................
8

Fi
gure 9 Beer Test 1

................................
................................
................................
..........................

11

Figure 10 Whiskey Test 1
................................
................................
................................
...................

11

Figure 11 Beer Test 2

................................
................................
................................
........................

11

Figure 12 Whiskey Test 2
................................
................................
................................
...................

11

Figu
re 13 Time Line
................................
................................
................................
...........................

12

Figure 14 Budget and Part List

................................
................................
................................
...........

12











v



Summary


The purpose of this project is to demonstrate the k
nowledge acquired while completing

the
Electronics Engineering program. The project will cover all aspects including, programming
knowledge, know
ledge of the operation of micro
controllers/processors,
as well as
electronic
circuit knowledg
e, design and assembly. The demonstration of

other important

skills such as
troubleshooting
, technical knowledge and report writing

is also required
.

The Alcohol

Detector
is a device that senses a change in the
alcoholic gas content of

the
surrounding

air.

The sensor will then anal
yze the amount of alcoholic vapors

and offer the user
some indication of the amount of alcohol present.
Th
is device is more commonly
referred to a
s
a breathalyzer; as it analyzes

the alcohol content on a person’s
breath
.
The device is mostly
used by law enforcement to determine whether an individual has been driving under the
influence of alcohol. Police breathalyzers measures the Blood

Alcohol Content, or BAC, of an
individual.
The unit designed for this project is a simpler
version of the breathalyzer used

by
police. I
t

will not

accurately

determine the BAC level of a person; however it will provide a
guide as to whether or not you sho
uld operate a motor vehicle after drinking alcohol.

This project is an attempt to build a useable Alcohol Detector with the
PIC16F
57

microcontroller

with
out utilizing an analog to digital converter
. The microcontroller is
interfaced with a MQ
-
3 alcohol gas sensor, which serves as the
analog
input signal

to the
controller
. There are

a string of six

LEDs
attached to six

output pins that
will function

as a
display.

Depending on the amount of alcohol p
resent, the MQ
-
3 sensor will analyze its con
tents
and consequently the

sensor

outp
ut voltage will increase. If output voltage increases enough,
input pins on the microcontroller will change from active low

state

to active high

state
.
Depending on which inp
uts go high, corresponding LEDs will illuminate to allow user to see
their personal alcohol content.

Main issues that occurred with
the construction an alcohol gas tester include
impl
ementing the
PIC16F57

microcontroller board into the design,
the programming of the microcontroller, the
locating and
availability of an acceptable alcohol sensor,
and
devising acceptable means of
testing.

Each issue

was confronted
throughout
the designing, construction process.


1



1.0
Introduction

1.1
Overview


A
n Alcohol Gas Detector or “Breathalyzer,” is a device used to determine the Blood Alcohol
Content, or BAC, of an individual

(“Blood Alcohol Levels”)
. A person’s BAC must
be
below a
certain level in order to operate a motor vehicle legally. When a user exhales into a
breathalyzer, an alcoholic sensor detects the ethanol vapors present. Through a chemical
reaction, the ethanol is oxidized into an
acetic
acid

(“Oxidation/Reducti
on Reactions”)
.

The
overall reaction will produce an electrical current which can be measured by a microprocessor,
and the information converted into an approximation of a person’s BAC. For the purposes of
this project,
the alcohol detector constructed

wil
l not accurately measure a users BAC, but will
follow its principal theories, and offer more of a guide line.


1.2
Basic Design and Operation


The
Alcohol Detector

will analyze alcohol

content in the air and then send an analog signal to
the micro proces
sor for analysis
. The Alcohol Detector

will
consist of three main areas
:



The alcohol detector

sensor

circuitry



The PIC16F57

microcontroller



LED display circuitry

The alcohol detector circuitry consists of the MQ
-
3 alcohol sensor,
one 10k ohm potentiometer,

one 10k load resistor,

two

100
0

ohm resistors

a 3300 ohm resister

and a 100 ohm
. The circuitry
is powered by its own 6 volt battery pack. The output of the MQ
-
3 alcohol sensor is regulated
by the 10k potentiometer. The output of the MQ
-
3 sensor is connect
ed to
a voltage
divider
(Floyd)
, two

100
0

ohm

and a 3300 ohms resister in series
;

e
ach
section of the divider

is
connected to one of three inputs on the microcontroller.

The microcontroller
is the PIC16F57
. It is a 16 pin I/O microprocessor

that uses Basi
c Stamp 2
programming language
. The program compiled for this project uses P0
-
P5 as outputs, and P9,
P11 and P13 as inputs. If the output from the MQ
-
3 sensor allow
s for one or more input pins

to
go from active
low (
0
-
1.1V)

to active
high (
1.3
-
5V)

(Kleitz)
, corresponding outputs will turn on
LEDs.

2



The display circuitry is made of six LEDs. Each LED is connected to an output pin on the
micr
ocontroller through 270

ohm resistors. Depending on the input

voltage, the
microcontroller

issue
s

commands to light corresponding LEDs.




2.0
Main
Components


2.1
MQ
-
3 Alcohol Sensor



Figure
1

MQ
-
3 Sensor

Source: www.pololu.com



The MQ
-
3 alcohol sensor
, (
F
igure 1
)
, is the sensor used for this project. It detects
the
concentration of alcohol
gas

in the surrounding air
. It then
outputs its reading as an analog
voltage
. The Sensor

has a
sensing range of 0.05

mg/L to 10

mg/L
. The
legal BAC in Canada is
0.08

gra
ms per 2
10

litres, or 0.38

mg/L

(“Blood Alcohol Levels”)
.
The sensor is
very sensitive to
alcoholic content present
and has an appropriate range of detection.
The response time for
measuri
ng

in alcohol content is quick and i
t can
operate at temperatures from
-
10
to 50°C.

The
MQ
-
3 s
enor meets the criteria required

to allow it to serve as the

sensor for this project.


3



When a

use
r exhales into the
alcohol sensor, any ethanol present in their breath is oxidized to
acetic acid
, an organic acid
.

The resulting chemical

reaction will produce an electrical current.

The difference of potential

produced by this reaction is measured, processed, and displayed as
an approximation o
f overall blood alcohol content.


2.1.1
MQ
-
3
Operation


The MQ
-
3 has six contacts as shown in Fig
ure 2. There is no polarization on the sensor so either
contacts A or B could be used interchangeably as Vcc and Ground. The contacts labeled as H are
the contacts for the internal heating system.

The internal heating system is a small tube made of aluminu
m oxide and tin dioxide
.
Inside this
tube, there are heating coils

which produce the heat
. These coils can draw up to 150mA of
current.
The alumina tube is covered with the tin dioxide, SnO
2
, embedded between the SnO
2

and the alumina tube is an Aurum electrode,
(
see Figure 3
)
. When heated, the SnO
2
become a
semiconductor and produces movable electrons. These movable electrons allow for the follow
of more current. When alcohol
molecules

contact the
electrode
, the alcoho
l
chemically

changes
into

acetic acid

and produces a flow of current within the tube.

The more alcohol present the
more current is produced.



Figure
2

MQ
-
3 Contacts

Source: www.sensorworkshop.com


4










Figure
3

Heating Tube
Source: www.sensorworkshop.com




The current however is not what is
measured

when
measuring

the output
,

w
hat is measured is
the voltage between the
output

of the sensor and the load resistor
.
Also inside the sensor there
is a variabl
e resistor across contact
s

A and B. The resistance between the contact
s

A and B will
vary depending on the amount of alcohol present. As the amount of alcohol increase, the
internal resistance will decrease and thus the voltage at the ou
tput will increase.

This
voltage

is

the analog signal transmitted to the microcontroller.

2.2 MQ Carrier Board

The MQ carrier board
,
(
Figure 4
)
,
is a printed circuit board or PCB.
This PCB
is compatible with
all MQ gas Sensor models and
reduces the six contacts

to an easier to manage
layout of
three
pin
s
.
The three pins are Vcc, Ground and Output. Depending on your choice of positioning of
the MQ sensor on the PCB, it will connect both A contacts to the Output pin and A side H
contact to Ground, and both B conta
cts and B side H contact to Vcc.



Figure
4

MQ Sensor Board

Source: www.pololu.com


5




2.3 Parallax SumoBot Circuit Board


The microcontroller used to analyze the input data is the
PIC16F57
. The IC is mounted on

the
Parallax SumoBot board which

is used with the Sumo Robotics kit. Some of the features this
board includes are a regulated 5v power supply

(Vdd)
, an unregulated 6v power
supply

(Vin)

and 16
Input/output
, I/O pins. The board itself is powered by a 6v ba
ttery pack. The
microcontroller

uses Basic Stamp 2
programming

language. This microcontroller was
chosen

for
the

memory space available, the amount of I/O pins available.



Figure
5

SumoBot Board

Source: www.parallax.com







6



3.0 Design and Construction


3.1 Sensor Circuitry


The design of the Gas Analyzer
required

its own localized circuit
, (see Figure6)
.

The MQ
-
3
sensor Vcc requires 5v Ac or Dc. The internal heater tube requires up to 150mA of current. The
Vdd 5v power output on the Sumoboard can only produce up

to

20mA of current. This resulted
in a separate 6v battery pack to power the MQ
-
3 sensor.

A 1
0k ohm
potentiometer

is used to
calibrate the sensor as well as
regulate the output
v
oltage
.
Although the data sheet for the MQ
-
3 sensor recommends 200k as a load resister, to offer
higher output voltages from the sensor a 10k ohm resister was used. The po
tentiometer set at
880ohms, and the 10k load resister form a voltage divider to allow a at rest output volta
ge for
the sensor to be at 1.0v
.

The output of the sensor is connected to
a voltage divider consisting of a
1k ohm
, 1k ohm, 3.3k
ohm
and a 100
resistor
.
After each phase of the divider,
there
is

a connection

to three inputs of
the microcontroller. As the alcohol content increases around the sensor, the output voltage will
increase from
1.0v
.


Figure
6

Sensor
Circuitry

Source: Original

7





3.1.1 Voltage Divider



Figure
7

Volt Divider

Source: Original


The voltage divider divides the MQ
-
3 sensor output voltage into three
separate

voltages. After
e
ach section of the divider, an
input of the mic
rocontroller will check to see

if the voltage i
s
enough to change to

active high. In order to go from a low to a high state

(Kleitz)
, the voltage at
the input must be over 1.3v.

Example: The presents of alcohol causes the MQ
-
3 output voltage increases to
2.5v, the voltage
at P9 will be [
(R4+R5+R6)/(R3+R4+R5+R6)] * 2.5 = 2.04v. 2.04v will make P9 change from low to
high. The voltage at P11 will be [(R5+R6)/(R3+R4+R5+R6)] * 2.5 = 1.57v, P11 will also change
from low to high.





(Floyd)



8





3.2 Display Circuitry


The display circuitry consists of six LEDs connected to output pins P0 through P5. The LEDs are
each protected by 270 ohm resisters. Depending on the input signal into the microcontroller,
different output pin
s

will activ
ate.
See Figure 6 for schematic.





Figure
8

Display Circuitry
Source: Original








9




4.0

Gas Analyzer
Operation


4.1
Explanation


T
esting of the alcohol content begins by powering the microcontroller and the MQ
-
3 sensor.
With
the sensor powered, approximately ten second is required to allow for the internal heater
coil to heat the tin dioxide, SnO
2

coating. Ten seconds is an appropriate time frame for the tin
dioxide to become a semiconductor. After the ten seconds, the analyze
r is ready
to begin
testing to alcohol.

When the ethanol
molecules

make contact with the Aurum electrode,
oxygen is added to the
ethanol and it begins to oxidize.

The ethanol is chemically changed, and the result is Acetic acid
and a bit of water.
The
oxidation of the ethanol produces an electrical current that will move
through the tin dioxide coating SnO
2
.

Conversion Process

CH
3
CH
2
OH
(ethanol)

+ O
2(oxygen)

=>=>=>
(oxidation)
=>=>=>

CH
3
COOH
(Acetic Acid
)

+ H
2
O
(water
)

(“Oxidation/Reduction Reactions”)


As the alcohol content in the air rises, the resistance between contact A and B will decrease
allowing more voltage at the output. The output of the sensor
is connected to
a voltage divider,
after each phase of the divider

there is connection made to

inpu
ts P9, P11, and P13 of the
micro controller respectfully. Each of these inputs are preset by the Basic Stamp program code
to an active low state
, 0
-
1.1v (Kleitz)
.
T
he output voltage from the sensor
needs
to
increase
from its rest
state of 1.0v

to a voltage

level
of
over 1.3v
,a logic level high (Kleitz),

at each divider
section.

If one or more pin is activated, the Basic Stamp Program will turn on the LED
lighting
sequence for that pin.





10




4.2 Calibration


MQ
-
3 Sensor Output
(V)

Input P9 Logic Level

Input

P11 Logic Level

Input P13 Logic Level

1.0v

(rest)

Low

Low

Low

1.
1
v


1.5v

Low

Low

Low

1.6v


2.1v

High

Low

Low

2.2v


3.5v

High

High

Low

3.6v + (saturation)

------

------

------


As shown in the above chart, using the voltage divider method,

there is a requirement of an
increase of approximately 600m volts at the sensor output to register a response on the
display.
For input P9 to go high, the sensor output must exceed 1.6v. Input P11
requires

at least
a sensor output of 2.2v

to change to hig
h
.
Input P13 cannot change from low to high before the
MQ
-
3 sensor goes into saturation. Withou
t

an analog to digital converter, this
is
the limitation
of the microcontroller.

Utilizing an analog to digital converter would provide more accurate
results.


The alcoholic agent
s

used for testing t
he calibration were Alpine Lager beer produced by

Moosehead

Breweries, and Crown Royal produced by the
Diageo

group
.
The

charts

below

show
the
tests preformed over a period of four days. The time laps column indicate
the amount of
time that has past, consumed column the amount of alcohol consumed during that
period

of
time
, and

sensor
output
is the voltage recorded. The
four

tests are shown

below

two
beers
,

two
whiskeys
.

The test data show some interesting results.
The sensor output data throughout the time laps
and different types of alcohol consumed, increase roughly the same amount.

The highest
voltage level recorded was 2.8volts, it occurred with both the in a whiskey and a beer test. After
the first time frame,
for beer and whiskey tests, the output was high enough to set Input11 high
and light the yellow LED segment of the display.
Due to the effect the alcohol
consumption
had

on the tester, this segment is

used to tell the user that they should not operate a

ve
hicle.

Also
as stated in the calibration table, the max output voltage recorded
,
2.8volts
,

is not e
nough to
trigger input13

high.



11




4.2.1 Test Data


Time laps (min)

Beer Consumed (bottle)

Sensor Output (V)

30min

2.0

1.8
v

60min

4.0

2.
5
v

90min

5.0

2.
7
v

120min

6.0

2.
6
v

Figure
9

Beer Test 1


Time laps (min)

Whiskey Consumed (
2oz shot
)

Sensor Output (V)

30min

2.0

1.9
v

60min

3.0

2.
3
v

90min

4.0

2.
5
v

120min

5.0

2.
6
v

Figure
10

Whiskey Test 1


Time laps
(min)

Beer Consumed (bottle)

Sensor Output (V)

30min

2.0

2.0
v

60min

4.0

2.4
v

90min

5.0

2.
6
v

120min

6.0

2.
8
v

Figure
11

Beer Test 2


Time laps (min)

Beer Consumed (bottle)

Sensor Output (V)

30min

2.0

1.
9
v

60min

3.0

2.4
v

90min

4
.0

2.
8
v

120min

5
.0

2.
7
v

Figure
12

Whiskey Test 2




12



5.0 Information


5.1 Time Frame



Figure
13

Time Line


5.2 Budget

and Part List


Part Name

Quantity

Total Price ($)


MQ
-
3 Sensor

1

4.95

MQ Sensor PCB

1

0.95

10k ohm
Potentiometer


1


1.95

10k Resistor

1

0.20

3300 ohm Resistor

1

0.20

1000 ohm Resistor

2

0.50

270 ohm Resistor

6

1.50

100 ohm Resistor

1

0.10

Green LED

3

0.70

Yellow LED

2

0.40

Red LED

1

0.20

SumoBot Board (PIC)

1

139.00

Man Hours

75

8500.00



Total = 8650
.65

Figure
14

Budget and Part List









13





6.0 Conclusion and Recommendations


The Gas Analyzer

in the end was able to detect the change in the output voltage, analyze and
then dis
play

an estimate

of the alcohol content of a person’s breath.

The tests indicated that
consuming for drinks of alcohol with a one hour time frame was enough to increase the sensor
output voltage above 2.2 volts, which was decided to be the threshold of being o
ver the legal
limit of alcohol in the blood stream.


The limitations of using a voltage divider to issue input signals to the
microcontroller

became
apparent when it was discovered that
the MQ
-
3 sensor could not produce a high enough
output voltage

to
divide down to at least
1.3

volts at the third division on the voltage divider.
After dividing the voltage twice there was simply not enough make Input13 change to active
high.
After an output voltage of approximately 3.5 volts, the sensor would become sat
urated
and require a longer than normal cool down time. The MQ
-
3 sensor itself an excellent piece of
equipment, its capabilities, used with an analog
digital converter could

give a
very accurate
account of a person blood alcohol level
.

One
recommendation

for

any improvement one might employ on this project is to use a analog
to digital converter. The converter will be able to take the output voltage signal directly from
the sensor and convert into a digital signal. Depending of the strength signal, a micro
controller

could accurately assess and distribute the output signals.











14



References Cited


Floyd, Thomas L..
Principles of Electric Circuits: Conventional Current Version (8
th

Edition) (Floyd
Principles of Electric Circuits Series).
Alexandria,

VA: Prentice Hall, 2006.


Kleitz, William.
Digital Electronics: A Practical Approach (8
th

Edition).
Alexandria, VA: Prentice
Hall, 2007.


Wicks, Kurt.

Oxidation/Reduction Reactions.

01

May

2011
http://www.chemistrylecturenotes.com/html/oxidation___reduction_reaction.html


“Blood Alcohol Levels.”
Blood Alcohol Levels
.
05

May 2011
http://www.upei.ca/~stuserv/alcohol/bac1.htm


“Sensor Workshop.”
Sensor Report


MQ
-
3 Gas Sensor
.
21 April 2011
http://sensorwork
shop.blogspot.com/2008/04/sensor
-
report
-
mq3
-
gas
-
sensor.html



















15




APPENDEX


















16



Basic Stamp Code

Flowchart




17



Basic Stamp Source Code


' {$STAMP BS2}

' {$PBASIC 2.5}

'

'
=========================================================================



'
-----
[ Program Description ]
---------------------------------------------

' Breathalyzer Program v4.0

' By Sean Enright

' Program will read oupt from MQ
-
3 senor. If senor output
triggers active high

' on either input IN9, IN11, or IN13, corresponding LEDs will activate



'
-----
[ I/O Definitions ]
-------------------------------------------------


LEDs VAR OUTL ' LEDs on P0
-

P5

LEDsDirs

VAR DIRL ' DIRS control for LEDs



'
-----
[ Constants ]
-------------------------------------------------------


Delay CON 10000 ' Allow Sensor to Heat

Delay2 CON 15000
' Delay time for LEDs



'
-----
[ Initialization ]
--------------------------------------------------


Reset:

OUT9 = 0 ' Set IN9 active low

OUT11 = 0 ' Set IN11 active low

OUT13 = 0

' Set IN13 active low


LEDS = %000001 ' start with P0 LED on


LEDsDirs = %111111 ' make LEDs outputs




'
-----
[ Program Code ]
----------------------------------------
------------


Konaha: ' Start

PAUSE Delay ' Wait 10 seconds

LEDS = %000000 ' LEDs off


Zabatsu: ' Scenario 1

IF IN11 = 1 THEN Kazeshini ' INPUT Goes High go to Sub

GOTO Zengetsu ' Jump to Next Scenario

18



Zengetsu: ' Scenario 2

IF IN9 = 1 THEN Kakashi ' INPUT

Goes High go to Sub

GOTO Zabuza ' Jump to Next Scenario


Zabuza: ' Scenario 3

IF IN13 = 1 THEN Kenpachi ' INPUT Goes High, go to Sub

GOTO Konaha

' Return to Start


END ' End Of Program


'
-------
[ Subroutines ]
---------------------------------------------------------

Kenpachi: ' Scenario 1

LEDs = %000111

' LEDs P0
-
P3 light

PAUSE Delay2 ' Stay Lit 15 sec

Leds = %000001 ' P0 stay Lit

RETURN


Kazeshini: ' Scenario 2

LEDs = %011111

' LEDs P0
-
P4 light

PAUSE Delay2 ' Stay Lit 15 sec

Leds = %000001 ' P0 stay Lit

RETURN


Kakashi: ' Scenario 3

LEDs = %111111

' LEDs P0
-
P5 light

PAUSE Delay2 ' Stay Lit 15 sec

Leds = %000001 ' P0 stay Lit

RETURN




19





MQ
-
3 Sensor Data
Sheet

20




21




22



Sean Enright

19 Donaldson St

Saint John, NB


May 27, 2011


Steve Adamson

Instructor

New Brunswick Community College

950 Grandview Avenue

Saint John, NB



Subject:
Senior Technical Project


Dear Mr. Adamson


This is a letter of transmittal for my Senior Technical Project. The project is to desig
n and

construct an alcoholic gas

detector.



The alcohol gas
detector

will consist of a microcontroller being implemented within a circuit.
The data will be gathered by an alcohol sensor and will be distributed to the microcontroller for
analysis. The microcont
roller will then indicate on a LED string display the amount of alcohol
present.

The primary designer, programmer, tester and constructor will be Sean Enright using the
acquired knowledge, resources, materials, skill sets learned through personal research,

information provided by instructors and academic knowledge acquired through Electronics
Engineering Technology Program at NBCC Saint John.

After reviewing the proposal, if you have any questions or comments, please reach me via email
at
enrighse@saintjohn.nbcc.nb.ca
, or phone at 506
-
650
-
3611. I look forward to hearing back
from you on this matter.


Sincerely,


Sean Enright