Identify diagram: security

Showing posts with label security. Show all posts

Sunday, 19 May 2013

Simple Digital Security System

You can use this simple and reliable
security system as a watchdog
by installing the sensing
loops around your building. You have
to stretch the loop wires two feet above
the ground to sense the unauthorised
entry into your premises.
Wire loops 1, 2 and 4 are connected
to the A, B and C inputs of 7-segment
decoder 4511 (IC1), respectively, while
the D input of IC1 is grounded permanently.
The loops are also connected to
a dual 3-input NOR gate and inverter
CD4000 (IC2) to activate the alarm.

Fig. 1 shows the circuit of the digital
security system, while Fig. 2 shows
the proposed wiring diagram for the
loops around the premises. Before using
this security system, make sure
that loops shown in Fig. 2 are con-
�� PHERDAUS ISLAM nected as shown in Fig. 1. If you don’t
want to use a buzzer, switch it off by
opening switch S2.
The circuit works off a 9V regulated
power supply. However, battery
back-up is recommended. A commoncathode,
7-segment display (LTS543)
is used for displaying whether the
loops are intact or not.
If loop 1 is broken, the display will
show ‘1’. If two or all the three loops
are broken, the display will show the
sum of the respective broken loop

Sunday, 7 April 2013

Security System Switcher

An audio signal can be used as a form of input to control any security system. For example, an automatic security camera can be configured to respond to a knock on the door. The circuit described here allows the security system to automatic in on state. It uses a transducer to detect intruders and a 5V regulated DC power supply provides power to the circuit.

As shown in Fig. 1, a condenser microphone is connected to the input of small signal Pre- amplifier built around transistor T1. Biasing resistor R1 determines to a large extent the microphone sensitivity. A microphone usually has an internal FET which requires a bias voltage to operate. The sound picked up by the microphone is amplified and fed to input pin 2 of IC1 (LMC555) wired in monostable configuration.

Fig. 1: Schematic Security system switcher Circuit diagram :

IC2 (CD4538B) is a dual, precision monostable multivibrator with independent trigger and reset controls. The output of IC1 is connected to the first trigger input pin 4 of IC2(A) through switch S1. If an intruder opens or breaks the door, IC1 is triggered by sound signals; the timer output pin 3 of IC1 goes high and enables first monostable multivibrator IC2(A). IC2(A) provides a time period of around 5 to 125 seconds, which is adjusted with preset VR1.

Another monostable multivibrator IC2(B) also provides a time period of around 25 to 600 seconds, which is adjusted with preset VR2. The output of IC2(B) is used to energise relay RL1. Indicator LED1 is provided to display the relay activity. Any AC/DC operated security gadget is activated or deactivated through a security switch. Thus, the security switch of the gadget is connected in the n/o contacts of the relay.You can also operate high power beacons, sirens or hooters in place of the security switch for any AC/DC operated security gadget.

Fig. 2: Proposed cabinet :

Assemble the circuit on a general-purpose PCB and enclose it in a cabinet as shown in Fig. 2 along with 5V adaptor for powering the circuit. Connect the security switch according to the circuit diagram and use appropriate AC/DC power supply required to operate the security gadget.

Warning! All relevant electrical safety precautions should be taken when connecting mains power supply to the relay contacts. With the help of single pole double throw (SPDT) switch S1, internal or external trigger input (active high signal) can be selected.

Source : http://www.ecircuitslab.com/2012/07/schematic-security-system-switcher.html