Alarm Consolidation for the Deaf

1. Group 17 Mukta Vaidya & Timothy O'Brien ECE 445 Nov. 28, 2007 Alarm Consolidation for the Deaf

2. Introduction • No comprehensive system satisfies the needs of those who are deaf or hard of hearing • Nationwide Safety Mandates • USFA Survey *1

3. 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

4. Highly accurate CO & smoke sensor units • Microphone and filter compatible with existing audible alarms • Easy installation and portability Product Features

5. Strobe light to warn deaf & hard of hearing users of a triggered alarm • Portable vibration unit to alert users when asleep Product Features

6. 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 Current Market Products

7. 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 Smoke Gain Circuit CO Gain Circuit RMS to DC Converter Output Trigger Relay Strobe Vibration Unit

8. Optical Smoke Sensor • Fairchild QEC121 Infrared LED • Fairchild L14C1 Phototransistor • Developed cover to protect detector from ambient light, dust, etc. Smoke Detector Collector Scattered Light “Hits” Base Smoke Particles Base Emission from LED Emitter Anode Cathode

9. 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 Smoke Detector

10. 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

11. 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

12. 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

13. 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 *2

14. Filter Block Diagram Fourth Order Butterworth Low Pass Filter Fourth Order Butterworth High Pass Filter Fourth Order Butterworth High Pass Filter *3

15. 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 Filter Design *4

16. Frequency Response 3.5kHz range

17. 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)

18. 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

19. 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

20. 12VDC 3 Amp Relays • Single Pole Double Throw switches • Inputs taken from all three modules • Outputs 15VDC to both the strobe and vibration motor Relay Switch

21. 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

22. 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

23. 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

24. 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 Challenges

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

26. 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 Challenges

27. 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 Challenges

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

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

30. 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

31. 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 Ethical Considerations

32. 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

33. We'd like to thank...

34. 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