Smoke Detector

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Smoke Detector
∗ Sardar

Nimisha Sankhe∗ , Nisarg Vinod† and Ekta Vira Patel Institute of Technology, Mumbai-400058, India, † Sardar Patel Institute of Technology, Mumbai-400058, India, ‡ Sardar Patel Institute of Technology, Mumbai-400058, India, ekta

Abstract Most of the smoke alarms available in the market use one or another kind of smoke sensor which increases the cost and also require complicated interfacing circuitry around it. But this smoke alarm circuit uses readily available photon-coupled interrupter module as smoke detector. The functioning of this smoke alarm is to continuously detect smoke and automatically activate the alarm in case of dense smoke. Loud sound is heard continuously indicating the presence of smoke till smoke clears. After this, the circuit is automatically reset for further detection of smoke provided it is kept in power ON condition.

I. I NTRODUCTION A smoke detector is a device that contains a physical mechanism or electronic sensor that quantifies smoke that can be integrated with or connected to other devices that detect the presence of smoke within an enclosed space. 1) Theory : Smoke detection technology was developed from a very primitive times by use of chemicals but the electronic way of its implementation had a profound effect on efficiency in detecting smoke. The basic idea is to detect the change in air density due to smoke and give out an alarm. The first home smoke detectors were invented by Duane D. Pearsall in 1967. 2) Methods of Implementation : a) Chemical Detectors : Most of the times, smoke is caused by fire or ignition. Hence by detecting gases in particular environment we can predict about presence of smoke. These detectors use Carbon Monoxide (CO) or Carbon Dioxide (CO2 ) sensors which sense level of these gases in atmosphere and activate alarm accordingly. But these detectors are not accurate enough to be implemented. b) Ionisation Detectors : This type of detector is cheaper than the optical detector, however it is sometimes rejected for environmental reasons. It can detect particles of smoke that are too small to be visible. It includes a tiny mass of radioactive Americium-241 (Am241 ), which is a source of alpha radiation. The radiation passes through an ionization chamber, which is an air-filled space between two electrodes, and permits a small, constant current to flow between the electrodes. Any smoke that enters the chamber absorbs the alpha particles, which reduces the ionization and interrupts this flow of current, setting off the alarm. c) Light Intensity Based Detectors : i) Using Light Dependent Resistor (L.D.R.) : L.D.R. has property of changing its resistance depending upon incident light. Hence when smoke cloud is formed over L.D.R., light intensity reduces and subsequently alarm gets activated. ii) Using Photon coupled Interrupter Module : This consists of an infra-red L.E.D. and phototransistor. When smoke comes in between slot, infra-red light beam, gets obstructed and transistor goes off i.e. it acts as open switch. Hence by using transistor ON-OFF conditions we can activate the alarm when smoke is present. [1]


3) Applications : Photoelectric smoke alarms are designed for residential and commercial purpose such as homes, apartments, hospitals, hotels and most importantly industries. They are engineered to virtually eliminate nuisance alarms and deliver outstanding performance wherever reliable fire and smoke protection is required. The smoke detection and warning system has never ending application in fire safety department. The smoke detection circuit has wide range of industrial application not only for the sake of fire safety but also in the field of development artificial sensory systems in future technologies. II. P ROPOSED C IRCUIT 1) Circuit Diagram :

Fig. 1: Smoke Detector using Photocoupler - Schematic Diagram 2) Working of Circuit : The basic idea behind circuit...
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