25 January 2015

Automatic Gate Alarm With Light

Abstract :-

The passive infrared detector (PIR) is one of the most common detectors found in household and small business environments because it offers affordable and reliable functionality. The term passive refers to the fact that the detector is able to function without the need to generate and radiate its own energy. 

This system which is installed at the gate uses an IR transmitter sensor unit to identify the arrival of a person and makes a beep sound using a buzzer. This system also switches on the gate light when surrounding light is low. The light glows only for a designed time interval and thus it helps a lot in saving electricity. This is basically a detecting mechanism project.


Burglary of residences, retail establishments, and other commercial facilities involves breaking and entering, and stealing property. Attempted forcible entry into a property is also classified as burglary, in the FBI's Uniform Crime Reports (UCR) definition.

PIRs verify if an intruder or object is actually there. Creating individual zones of detection where each zone comprises one or more layers can achieve differentiation. Between the zones there are areas of no sensitivity (dead zones) that are used by the sensor for comparison.

The circuit may be used to automatically switch on a light at the entrance gate to the premises at night by sensing the presence of a person. In addition, it sounds an alarm to signify the presence of a person. Here we are using an IR Led as the transmitting unit and the TSOP as receiving unit. A monostable, multivibrator circuit is used for the purpose of getting time delay accordingly. Lamp is switched on only for a short interval to save electricity. The main application is its use in restricted areas to indicate the entry of trespassers. It can also be used for security purposes. 

LDR (Light Dependent Resistor)

A light-dependent resistor alternatively called an LDR, photoresistor, photoconductor, or photocell, is a variable resistor whose value decreases with increasing incident light intensity. 

An LDR is made of a high-resistance semiconductor. If light falling on the device is of high enough frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electron (and its hole partner) conduct electricity, thereby lowering resistance. 

A photoelectric device can be either intrinsic or extrinsic. In intrinsic devices, the only available electrons are in the valence band, and hence the photon must have enough energy to excite the electron across the entire band gap. Extrinsic devices have impurities added, which have a ground state energy closer to the conduction band - since the electrons don't have as far to jump, lower energy photons (i.e. longer wavelengths and lower frequencies) are sufficient to trigger the device.


The astable multivibrator generates square wave of a particular frequency which is given as input to IR LED. The LED generates IR rays which are received by the TSOP receiver. When the IR rays get interrupted, a low output will be produced at the output terminal of TSOP. This is given as a trigger to the monostable MVB which in turn produces a high output. This high output is fed to the base of Q3 which pulls it to ground. The ground voltage comes to one of the two terminals of the buzzer and supply voltage is given to its other terminal. Thus the buzzer functions and indicates the presence of a person. 

During night, when no light falls on LDR, it has high resistance. So low voltage comes in the base of Q2 and it goes OFF. This results in a high voltage at the base of Q1 and it is pulled to ground. So the relay is de-energized and this shifts the switch contact from position 5 to 4.Thus supply voltage comes to one terminal of bulb whose other terminal is grounded and the bulb is switched on. During daytime when light falls on LDR its resistance goes low.


The project provides the detecting mechanism of objects or person at unexpected timings. The project is user-friendly and highly reliable. This project has the advantage of saving of electricity since the bulb glows in the dark only for a short interval of time. Another main advantage which we could point out is the height adjusting mechanism which we could implement.

With the use of high intensity alarms this can also be used for security purposes. Thus it turns out to be a domestic as well as security purpose project. System reliability can be a problem when it causes nuisance alarms, false alarms, or fails to alarm when called for. Nuisance alarms occur when an unintended event evokes an alarm status by an otherwise properly working alarm system or when there is an alarm system malfunction that results in an alarm state. It is easier to know when there are false alarms, because the system is designed to react to that condition. Failure alarms are more troublesome because they usually require periodic testing to make sure the sensors are working and that the correct signals are getting through to the monitor. Some systems are designed to detect problems internally, such as low or dead batteries, loose connections, phone circuit trouble, etc. While earlier nuisance alarms could be set off by small disturbances, like insects or pets, newer model alarms have technology to measure the size/weight of the object causing the disturbance, and thus are able to decide how serious the threat is, which is especially useful in burglar alarms.


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