Posted by Circuits Arena on Sunday, 9 November 2014
DOOR SECURITY ALARM USING IC 555 is the artlcle explaining DOOR OPEN SECURITY ALARM 555 IC This circuit works when the human enter the room or office open door automatically activate the alar...
DOOR OPEN SECURITY ALARM 555 IC
This circuit works when the human enter the room or office open door automatically activate the alarm sound from the buzzer. It is the simple circuit we can make at home with low cost. Schematic circuit diagram shown below.
Working
I would like to explain in practical point of view the above circuit shows reed switch is installed at near door. Initially door is closed position the reed switch is normally open type. When the door is opened by someone, the reed switch near the magnet is
open and the base of Transistor Q1 goes low through the 10k Resistor R2,
and so Transistor Q1 is ON. At this time trigger pin 2 of the IC1
go low, it triggers the monostable built around IC NE555. Once
triggered, output pin 3 of IC1 goes high, and both Buzzer and
LED are turned on.
Capacitor C1 starts charging through the Transistor Q1. After
few seconds the Buzzer and LED will be automatically switched OFF. When
the door is closed the T ransistor base become high, Transistor Q1
goes OFF and the Capacitor C1 starts discharging through the
Resistor R4 is connected parallel with the capacitor C1. You
can change the time period of IC1 by changing the values of resistor R5
and capacitor C2
