2B-LIGHT ACTIVATED ALARM
This project can be used as morning alarm. It can be fitted inside the room to inform you the entry of stranger, thieves etc. Also it can be fitted in treasuries.
TECHNICAL DESCRIIPTION AND WORKING:-
This project has been developed and successfully tested OK in TV Engineer Technical Lab.
This project is such a project which can astonish you and your family and also the people who are not acquainted with electronics. For example, there are some people who go to the bed late but unable to wake-up in the morning. This project gives a bell as soon as there is morning light. As such this project only works when where is light. In this project an IC555, transistor BEL187 & a 12Volt relay have been used. Also one light dependent resistance [LDR] is used to act with light intensity.
The resistance of the LDR increases or decreases on the intensity of light, when light falls on LDR, its resistance decreases and in darkness the resistance increases. In this circuit IC 555 is used as a timer. Pin no. 4 of the IC is earthed through a 2.2K preset which keeps the Flip-Flop system of the IC at a high state in darkness. Pin no. 3 of the IC is the output pin & remains at a low state. The IC does not operate in this condition of darkness. But when light falls on LDR, the resistance of the LDR decreases, as a result of which, pin no. 4 of the IC gets positive voltage, the Flip-Flop system of the IC comes to low state and internal inverting amplifier of the IC comes to high state resulting a voltage develop at pin no. 3. This pin no. 3 voltage biases the transistor BEL 187 and the transistor operates the relay. When the relay is ON, the bell starts ringing.
NOTE:- Readers may note that the LDR is mounted in such a way that morning sun light directly falls on the LDR.
PRECAUTIONS WHILE ASSEMBLING THE PROJECT:-
- Check all the component as per the circuit specification.
- IC 555 should be mounted on IC base.
- Proper attention to be paid to the collector, base & emitter of BEL 187 before mounting.
- Take care in wiring the circuit to avoid loose connecton.
- Keep LDR in such a place so that the morning sun light falls directly on LDR.
LIST OF COMPONENTS
IC555 – 1
IC Base – 1
LDR – 1
Relay 6V or 12V / 150E – 1
Transistor TR1 BEL187 – 1
Diode D1 IN4001 – 1
R1 100K – 1
R2 330E – 1
R3 2K2 PRESET – 1
POT, WIRE AS REQUIRED.
BELL OR BUZZER – 1