Smoke Alarm

Smoke Alarm

In this project a smoke detection alarm system is discused. The optical sensor consists of an IR diode and a photodiode with a small gap in between. During normal condition the photodiode is receiving the IR signal from the IR diode. The photo interrupter module is used as the smoke detector, while timer 555 is wired in astable configuration as an AF oscillator for sounding alarm via a loudspeaker.

Circuit:

About the Circuit:

This project uses a 555 timer IC with an optical sensor to create a smoke detection alarm system. The optical sensor consists of an IR diode and a photodiode with a small gap in between. During normal condition the photodiode is receiving the IR signal from the IR diode. The presence of smoke interrupts the signal to the photodiode which in turn activates the 555 timer IC to generate alarm. The timer IC is configured as an astable multivibrator with a frequency in the audible range.

In the absence of any smoke, the gap of photo interrupter module is clear and the light from LED falls on the phototransistor through the slot. As a result, the collector of phototransistor is pulled towards ground. This causes reset pin 4 of IC 555 to go low. Accordingly, the timer is reset and hence the alarm does not sound.

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Burgular Alarm Using IC555

Burgular Alarm Using IC555

 Abstract:

This circuit uses an IC555 timer. I.C 555 is connected as comparator with pin 6 connected with positive supply, the output goes high-1 when the trigger pin 2 is at lower than 1/3 level of the supply voltage. The output goes low-0 when it is above 1/3. So small change in voltage of pin 2 is enough to change the output state of pin 3 from 1 to 0 and 0 to 1. The output has only two states high and low and can not remain in any intermediate stage. It is power by 9V battery for portable use. The circuit is economic in power consumption. Pin 4,6& 8 is connected to the positive supply and pin 1 is grounded.

      To detect the present robber we have used LDR and a source of light.
LDR is a special type of resistance whose value depends on the brightness of the light which is falling on it. It has a resistance of about 1 megaohms when in total darkness,but a resistance of only about 2-5 k ohms when brightly illuminated. It responds to a large part of the light spectrum.
      The source of light and LDR is so adjusted with a reflector that light will directly fall on the LDR but when robber enters inside then it will block the beam of light and LDR will be under darkness.
      We have made a potential divider circuit with LDR and 100 K variable resistance connected in series. Voltage is directly proportional to conductance so more voltage we will get by this divider when LDR is getting light and low voltage in darkness. Sensitiveness can be adjusted by variable resistance. Divided voltage is given to pin 2nd of 555. As soon as LDR gets dark the voltage of the pin 2 drops 1/3 of the supply voltage and pin 3 gets high and Buzzer Beeps.
For Demo we have used simple LED for LED1 may be Red or White Color

Components:-

1) 9V battery with switch
2)LDR(Light Dependent Resistance)
3)Variable resistance
4)Resistance
5)LED(Light Emitting Diode)
6)IC 555 timer
7)Switch

Circuit Diagram:

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