Wireless Smoke Detector System

1
Wireless Smoke Detector System
ECE 445

• Andrew Chiu
• Chi-Ming Wang

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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

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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)

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Design Overview
Transmitter
Tone Generator
Receiver
PIC Microcontroller
Smoke Sensor
Temperature Sensor
Low Battery Sensor
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Smoke Detector
7
Temperature Sensor

• LM235AH
• Temperature threshold of 125F
• 10mV / Kelvin K
• 125F 324.67 K
• 324.67 K 10mV/K 3.2467 V
• Distinct alarm
• 4 kHz (lower resistance than smoke sensor for
  higher volume)
• Testing

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Temperature Sensor (cont.)

• Schematic

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Smoke Sensor

• 276-142, 279-143
• Detects smoke to serve as an early fire warning
• T-Shaped chamber (no smoke present)

LED
phototransistor
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Smoke Sensor (cont.)

• T-Shaped chamber (smoke present)

LED
phototransistor

• Distinct alarm
• 4 kHz (higher resistance than temperature sensor
  for lower volume)

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Smoke Sensor (cont.)

• Mechanical Drawing / Schematic

• Testing
• R1 determines the sensitivity

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Smoke Sensor (cont.)
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Smoke Sensor (cont.)
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Tone Generator

• LM555 Timer
• Produces four distinct sounds
• Low battery alarm gt 500 Hz
• Smoke alarm gt 4 kHz
• Temperature alarm gt 4 kHz (Higher volume)
• Receiving Alarm gt 2 kHz

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Tone Generator (cont.)

• Frequency1/(t1t2)
• t10.693 Ra C
• t2RaRb/(RaRb) ln(Rb-2Ra)/(2Rb-Ra)

From LM555 Datasheet
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Tone Generator (cont.)

• Schematic

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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

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Transmitter/Receiver (cont.)

• Schematic

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Transmitter/Receiver (cont.)
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Transmitter/Receiver (cont.)
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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

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Low Battery Sensor (cont.)

• Battery life (600 mA-hours / 150 mA)

4 hours
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Low Battery Sensor (cont.)

• Schematic

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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

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PIC Microcontroller (cont.)

• Prioritizes alarms based on safety level
• Testing
• Flow Diagram (next slide)

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Temperature Sensor Temperature threshold of 125F
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
detectors transmitter?
Yes
No
Always
Low Battery Sensor Battery measured below 3.5V?
Transmitter
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PIC Microcontroller (cont.)

• Schematic

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Unit Cost
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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

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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

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Complications Recommended Solutions

• Increase battery life
• Decrease the amount of powering up and powering
  down of the transmitter and receiver
• Cycle LED

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Thank You