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

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

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

System Overview Hardware Hardware Transmitter (RMX-900-HP3) Transmitter (RMX-900-HP3) Receiver (TMX-900-HP3) Receiver (TMX-900-HP3) Tone Generator (LM555CM) Tone Generator (LM555CM) Smoke Sensor ( , ) Smoke Sensor ( , ) Temperature Sensor (LM235AH) Temperature Sensor (LM235AH) Low Battery Sensor Low Battery Sensor Software Software PIC Microcontroller (C Language) PIC Microcontroller (C Language)

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

Smoke Detector

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

Temperature Sensor (cont.) Schematic Schematic

Smoke Sensor , , Detects smoke to serve as an early fire warning Detects smoke to serve as an early fire warning T-Shaped chamber (no smoke present) T-Shaped chamber (no smoke present) phototransistor LED

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

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

Smoke Sensor (cont.)

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

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

Tone Generator (cont.) Schematic Schematic

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

Transmitter/Receiver (cont.) Schematic Schematic

Transmitter/Receiver (cont.)

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

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

Low Battery Sensor (cont.) Schematic Schematic

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

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

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

PIC Microcontroller (cont.) Schematic Schematic

Unit Cost Part #ManufacturerDescriptionModule Needed For Price LM235AHNationalTemperature Sensor $5.49 RMX-900-HP3LinxReceiver $43.40 TMX-900-HP3LinxTransmitter $29.45 ANT-916-PW-LPLinxAntennaReceiver / Transmitter $1.79 PIC16F877AMicrochipPIC $ , Radio ShackLED and Phototransistor Smoke Sensor$3.29 PVC PipeHome DepotPVC PipeSmoke Sensor$2.99 MN1604B1ZDuracell9V Alkaline BatterySmoke Detector$1.99 LM555CMNationalTimerTone Generator$ ALS253ANECE Parts Store4-to-1 Dual MUXTone Generator$0.79 GC0401KCUISpeaker $2.99 Misc. (resistors, capacitors, etc.) ECE Parts StoreResistorsTesting Purposes$2.88 TOTAL$100.64

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

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

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

Thank You