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Wireless Smoke Detector System

Wireless Smoke Detector System. ECE 445. Andrew Chiu Chi-Ming Wang. Introduction. 400,000 residential fires each year in the US 50% of these occur in homes sans smoke detectors Currently, small market of wireless smoke detectors

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Wireless Smoke Detector System

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  1. Wireless Smoke Detector System ECE 445 Andrew Chiu Chi-Ming Wang

  2. Introduction • 400,000 residential fires each year in the US • 50% of these occur in homes sans smoke detectors • Currently, small market of wireless smoke detectors • Motivation to bolster home safety; enhancing smoke detectors accomplishes this

  3. Objective • Wireless network of smoke detectors • Benefits & Features • Increased safety • Wireless communication • Wide range of coverage • All detectors in the network are sounded if one detector is set off • Determine location of originating smoke or fire • Multiple alerts • Low battery warning

  4. System Overview • Hardware • Transmitter (RMX-900-HP3) • Receiver (TMX-900-HP3) • Tone Generator (LM555CM) • Smoke Sensor (276-142, 279-143) • Temperature Sensor (LM235AH) • Low Battery Sensor • Software • PIC Microcontroller (C Language)

  5. Design Overview Transmitter Receiver Tone Generator PIC Microcontroller Smoke Sensor Temperature Sensor Low Battery Sensor

  6. Smoke Detector

  7. Temperature Sensor • LM235AH • Temperature threshold of 125°F • 10mV / Kelvin [K] • 125°F = 324.67 K • 324.67 K * 10mV/K = 3.2467 V • Distinct alarm • 4 kHz (lower resistance than smoke sensor for higher volume) • Testing

  8. Temperature Sensor (cont.) • Schematic

  9. Smoke Sensor • 276-142, 279-143 • Detects smoke to serve as an early fire warning • T-Shaped chamber (no smoke present) LED phototransistor

  10. Smoke Sensor (cont.) • T-Shaped chamber (smoke present) LED phototransistor • Distinct alarm • 4 kHz (higher resistance than temperature sensor for lower volume)

  11. Smoke Sensor (cont.) • Mechanical Drawing / Schematic • Testing • R1 determines the sensitivity

  12. Smoke Sensor (cont.)

  13. Smoke Sensor (cont.)

  14. Tone Generator • LM555 Timer • Produces four distinct sounds • Low battery alarm => 500 Hz • Smoke alarm => 4 kHz • Temperature alarm => 4 kHz (Higher volume) • Receiving Alarm => 2 kHz

  15. Tone Generator (cont.) • Frequency=1/(t1+t2) • t1=0.693 * Ra * C • t2=[Ra*Rb/(Ra+Rb)] * ln[(Rb-2Ra)/(2Rb-Ra)] From LM555 Datasheet

  16. Tone Generator (cont.) • Schematic

  17. Transmitter/Receiver • LINX RXM-900-HP3 • LINX TXM-900-HP3 • Frequency = 919.87 MHz • Two signals • Off signal = digital High (about 5 Volts) • On signal = digital Low (about 0 Volts) • Distinct alarm • 2 kHz • Testing

  18. Transmitter/Receiver (cont.) • Schematic

  19. Transmitter/Receiver (cont.)

  20. Transmitter/Receiver (cont.)

  21. Low Battery Sensor • 3.5V threshold • Distinct alarm • 500 Hz • Testing • Entire system draws ~ 0.15 A • Power consumption ~ 0.8 W • Typical battery rating of 600 mA-hours

  22. Low Battery Sensor (cont.) • Battery life = (600 mA-hours / 150 mA) = 4 hours

  23. Low Battery Sensor (cont.) • Schematic

  24. PIC Microcontroller • Heart of the system • Processes signals from modules • Receives inputs from receiver, temperature sensor, smoke sensor, and low battery sensor • Outputs signals to tone generator and transmitter

  25. PIC Microcontroller (cont.) • Prioritizes alarms based on safety level • Testing • Flow Diagram (next slide)

  26. Temperature Sensor Temperature threshold of 125°F reached? Tone Generator Yes No Smoke Sensor Smoke detected? No PIC Microcontroller Temperature sensor, receiver, smoke sensor, or low battery sensor has been set off? Yes Yes No Receiver RF signal received from another detector’s transmitter? Yes No Always Low Battery Sensor Battery measured below 3.5V? Transmitter

  27. PIC Microcontroller (cont.) • Schematic

  28. Unit Cost

  29. Complications & Recommended Solutions • Dysfunctional parts • Transmitter / Receiver noise • Noise sources, wires, loop antennas • Solution: encoding signals, capacitors to filter noise from power supply, reduce board noise • Battery voltage fluctuation • Solution: secure battery holder/adapter, reduce wire length, do not daisy chain power wires

  30. Complications & Recommended Solutions • Implement on PCB • Cleaner signal between components • Less noise • More stable power • More compact • Use less expensive receiver and transmitter to decrease unit cost

  31. Complications & Recommended Solutions • Increase battery life • Decrease the amount of powering up and powering down of the transmitter and receiver • Cycle LED

  32. Thank You

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