Alarm Consolidation for the Deaf

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Alarm Consolidation for the Deaf

• Group 17
• Mukta Vaidya Timothy O'Brien
• ECE 445
• Nov. 28, 2007

2
Introduction

• No comprehensive system satisfies the needs of
  those who are deaf or hard of hearing
• Nationwide Safety Mandates
• USFA Survey

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Objectives

• Comprehensive hazard warning system tailored for
  the deaf and hard of hearing community
• Alerts individuals to the presence of smoke and
  carbon monoxide
• Also warns users upon the triggering of other
  generic smoke/CO alarms

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Product Features

• Highly accurate CO smoke sensor units
• Microphone and filter compatible with existing
  audible alarms
• Easy installation and portability

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Product Features

• Strobe light to warn deaf hard of hearing users
  of a triggered alarm
• Portable vibration unit to alert users when asleep

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Current Market Products

• Great Britain
• Smoke Alarm System (Sarabec EI 175)
• Contains both strobe and vibration unit
• Only accounts for smoke no Carbon Monoxide
• Retails for 181 USD
• United States
• ProductsForTheDeaf.com
• Supply smoke and carbon monoxide units separately
• Only smoke contains vibration unit
• Retails together for 490.90 USD

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Design Overview
CO Detector w/ MOS Sensor
Smoke Detector w/ Optical Sensor
Alarm Detector w/ Microphone

• Detection circuits
• Sensors
• Microphone Filter
• Amplifier Circuits
• Gain Circuits to 9VDC
• Outputs
• LED's
• Strobe
• Vibration Unit

Alarm LED's
Smoke LED's
CO LED's
Alarm Gain Circuit
CO Gain Circuit
Smoke Gain Circuit
RMS to DC Converter
Output Trigger Relay
Strobe
Vibration Unit
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Smoke Detector

• Optical Smoke Sensor
• Fairchild QEC121 Infrared LED
• Fairchild L14C1 Phototransistor
• Developed cover to protect detector from ambient
  light, dust, etc.

Collector
Scattered Light Hits Base
Smoke Particles
Base
Emission from LED
Emitter
Anode
Cathode
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Smoke Detector

• Impedance matched to output 3.5VDC when
  triggered
• Tested using 2 second constant stream of test
  smoke
• Received an average voltage change of .616VDC
  when tested over ten trials

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Carbon Monoxide Detector

• Electrochemical sensor capable of generating
  minute current for CO density in air
• Sensor response listed at 1.2-2.4nA/ppm of CO in
  air
• 30ppm is deemed hazardous
• Impedance matched the circuit loads to give a
  significant change in output voltage when
  triggered

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Carbon Monoxide Detector

• Figaro TGS 5042 Electrochemical sensor
• tiny chemical battery with two electrodes
• External short circuit drives current

CO Gas
Working Electrode
External Short
Alkaline Electrolyte
I
OH-, HCO3-, CO3-
Counter Electrode
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Carbon Monoxide Detector

• Testing Method
• Placed CO current source circuit behind exhaust
  of motor vehicle
• only means of testing without a controlled
  environment
• Results
• Average change of 15.2mV in the given trials

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Microphone Filter

• Microphone picks up other household alarms
• Butterworth bandpass filter used to isolate and
  trigger alarms around 3.5kHz
• Allows for compatibility with previously
  installed home safety systems

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Filter Block Diagram
Fourth Order Butterworth Low Pass Filter
Fourth Order Butterworth High Pass Filter
Fourth Order Butterworth High Pass Filter
3
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Filter Design

• Put in arbitrary m, Q, and R values to determine
  the capacitor ratio (n) and capacitor values (C,
  nC)
• Matched cut-off frequencies for high and
  low-pass components to peak around the 3.5kHz
  center frequency of the filter

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Frequency Response
3.5kHz range
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Filter Data and Requirements

• Determined 3dB Bandwidth to be 13.2 kHz
• Peak output voltage of 459mV at 3.5kHz for a
  2Vp-p sine wave
• Signal-to-noise Ratio of 53dB (ref 1mV)

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Filter Data and Requirements

• Microphone peak output of 100mV resulted in
  negligible output from filter
• Was not able to linearly amplify signal between
  microphone and filter
• Solution highlighted in Challenges

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Voltage Gain Circuits

• Each output from the respective alarm modules was
  passed through a corresponding non-inverting
  amplifier
• Used 9VDC as the voltage that would be sent to
  the relay switch to turn on the strobe light and
  vibration motor

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Relay Switch

• 12VDC 3 Amp Relays
• Single Pole Double Throw switches
• Inputs taken from all three modules
• Outputs 15VDC to both the strobe and vibration
  motor

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Strobe

• Strobe light to warn deaf and hard of hearing
  users of triggered alarm
• Strobe Federal Signal (175,000 Candle Power)
• Required Voltage 12V
• Current Drawn .530 A
• Power Consumption 6.36 W

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Vibration Unit

• Portable Vibration Unit to alert users when
  visual perception is not an option
• Motor
• Required Voltage 12V
• Current Drawn .450 A
• Power Consumption 5.4 W
• Motor Mounted and Attached to Weight

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Power Consumption

• Relay Signal Power
• 495mW when on
• Relay Load (strobe motor)
• 13.64W when on
• Filter, Amplifier, Microphone, Smoke Detector
  Circuits Combined
• 1.845W
• Total Power Consumption
• 16.475W when alarm is triggered
• 1.845W when in reading/standby mode

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Challenges

• Smoke photoelectric assembly reacted to changing
  levels in ambient light
• Output voltage increased an average of 30mV when
  ambient light was readily present
• Solution
• Built housing for smoke detector to reduce change
• Added potentiometer for our application to adjust
  sensor output to the amount of ambient light
  present

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Challenges

• Challenge Carbon monoxide sensor didn't give us
  its specified linear output.

• Solution
• Monitored behavior of sensor as current source
  in contrary to the active current to voltage
  conversion circuit suggested in the datasheet
• Build setup that provided stable step function
• Amplified step to produce desired output voltage
  for relay

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Challenges

• Could not get filter to output DC relative to
  frequency components
• Attempts to rectify and decouple the filter were
  unsuccessful
• Solution
• National Semiconductor LH0091 RMS to DC voltage
  converter could be added

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Challenges

• Voltage Follower Current Amplifier
• High current op-amp rated for only 310mA at 12VDC
• Destroyed several chips with current overload
• Solution
• 12VDC 4PDT 3 Amp relay switches provided enough
  power to run the strobe and vibration unit

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Challenges

• Battery Backup
• Could not invert negative supply voltage to
  compare with battery supply
• Inverting op amp requires constant supply of
  negative 15VDC

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Recommendations

• Test Sensors in Controlled Environment
• Use higher sensitivity microphone
• Attempt to fabricate negative supply voltage
  battery backup

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Cost Analysis

• Total Cost of Producing One Unit 115.42
• Most Expensive Component Strobe Light (77)?
• Estimated Cost of Mass Producing 1000 Units
  80,800

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Ethical Considerations

• By their very nature, household safety systems
  must be extremely reliable.
• Reliability stems from
• - Highly Accurate Sensing Units
• - Quick response
• - Battery Backup
• - Error alarm to detect when sensors are broken
• - Minimize false alarms

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In Summary...
We believe our consolidated safety system will
provide

• Heightened level of safety for deaf hard of
  hearing users
• Compliance with state and federal mandates
• Affordability (Cost Analysis)?
• Ease of use due to small scale of all-in-one
  apparatus and compatibility with other household
  safety systems

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We'd like to thank...
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Acknowledgements

• 1
• United States Fire Administration
• Fire Risks for the Deaf or Hard of Hearing
• http//www.usfa.dhs.gov/downloads/pdf/publications
  /hearing.pdf
• 2
• National Fire Protection Agency
• NFPA-72 National Fire Alarm Code
• 3
• Texas Instruments
• Analysis of the Sallen Key Architecture
• http//focus.ti.com/lit/an/sloa024b/sloa024b.pdf
• 4
• Image courtesy of answers.com