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1. ABSTRACT
Often we find that resedntial properties,offices,buildings etc suffer disastrous consequences due to a single short circuit or a simple fire which go undetected.To avoid such losses,one can make use of a smoke alarm which would in turn inform the concerned authority by sounding a buzzer or a sound as soon as any smoke is detected thereby avoiding danger as soon as it is detected.smoke alarm circuits today are used everywhere from resedential buildings to offices.
2. INTRODUCTION
The thermistor offers a low resistance at high temperature and high resistance at low temperature. This phenomenon is employed here for sensing the fire.The IC1 (NE555) is configured as a free running oscillator at audio frequency. The transistors T1 and T2 drive IC1. The output(pin 3) of IC1 is couples to base of transistor T3(SL100), which drives the speaker to generate alarm sound. The frequency of NE555 depends on the values of resistances R5 and R6 and capacitance C2.When thermistor becomes hot, it gives a low-resistance path for the positive voltage to the base of transistor T1 through diode D1 and resistance R2. Capacitor C1 charges up to the positive supply voltage and increases the the time for which the alarm is ON. The larger the value of C1, the larger the positive bias applied to the base of transistor T1 (BC548). As the collector of T1 is coupled to the base of transistor T2, the transistor T2 provides a positive voltage to pin 4 (reset) of IC1 (NE555). Resistor R4 is selected s0 that NE555 keeps inactive in the absence of the positive voltage. Diode D1 stops discharging of capacitor C1 when the thermistor is in connection with the positive supply voltage cools out and provides a high resistance path. It also inhibits the forward biasing of transistor T1.
3. BACKGROUND
Once the project title was given, firstly the needy teachers were consulted so as to provide us some direction to reach our goals.Keeping into mind the advice given,there was a search in reference books,as mentioned by the teachers for concrete ideas.Keeping into mind both the above points and consultation with our fellow colleagues,a final search on the internet took place to obtain an approximate circuit diagram that would match upto the ideas procurred so far and the datasheets of all the necessary components were too obtained in this manner.
4. WORKFOCUS
We intend on accomplishing the following things from this project:
1-To make a circuit that can be used to inform the necessary authority in the event of a fire.
2- To learn something practically as to how circuits are implemented in our day to day life.This could be called our first practical application of engineering.
5. METHODOLGY
Step 1: Procurement of circuit diagram:
Once the title of the project was given,the first step needed to be done was the procurement of an appropriate circuit diagram that would satisfy our needs.After a bit of research work on the needed ideas,components,advice from our fllow colleagues we were finally ready with the perfect circuit diagram needed for successful implemenation.we then moved on to step 2
Step 2:Implemenation of circuit on the breadboard:
As we had been taught,before implementing any circuit on the general purpose board(gpb) or the professional commercial board(pcb) it is necessary to check the validity of the circuit on the breadboard.The components were obtained from the shopkeepers and the circuit was first tested on the breadboard to check its effective working.Problems which were encountered were rectified at this stage itself.
Step 3:Implemenation of circuit on the general purpose board(gpb):
After completion of the first two steps,we moved onto the third step which was implemenation of circuit on either the general purpose board(gpb) or professional commercial board(pcb).We chose to implement the circuit on the general purpose board(gpb).The components were soldered and the circuit was ready on the gpb
Step 4:Testing of the circuit:
After the completion of the above three steps,the final step,that is the circuit mounted on the general purpose board was tested to check its effective working