In present days, burglar alarm systems have become necessary equipment in many stores as well as in homes.But, selecting a burglar alarm system for your home may often be confusing due to availability of different types. The basic burglar alarm is a magnetic switch sensor that includes a switch which opens and closes when it is near the magnet.

Burglar alarm systems are divided into two types. They are closed-circuit system and open- circuit system. In a closed circuit system, when the door is closed, the electric current flows through the circuit. So it triggers an alarm. In an open circuit system, when the door is opened, the electric current stops flowing through the circuit. Then the siren goes off.

Long-range Cordless Burglar Alarm Circuit

The long-range cordless burglar alarm circuit diagram is shown below which makes use of a CLT(cordless telephone) with a paging facility and a few low-cost discrete components. This circuit is so simple for a beginner as it can be easily built without any complexity. When the ‘page’ button on the cordless telephone is pressed and held in that position, the handset starts beeping to show that someone is calling. This function is used in this system to make the gadget. The burglar alarm system includes three sub-assemblies, such as wireless beeper, IR transmitter and IR receiver-cum-control unit.

Wireless Beeper:-This is the handset of a cordless telephone.

Infrared Transmitter

In the above infrared transmitter circuit, NE 555 timer is used as an astable multivibrator.The capacitor C1 is used to reduce ripples in the power supply. The 1st and 8th pin of the 555 timer is used to give power and ground respectively.The 4th pin is an active-low-input pin, which is connected to VDD, and the 5th pin is the voltage-control pin, which is connected to the ground through a capacitor to avoid high-frequency noises.The Resistors R1,R2 and the capacitor C2 decide the time period of oscillation.

The Capacitor C2 charges to VCC through the resistors R1, R2 and discharges through the 7th pin of the 555 timer and the resistor R2. The voltage across the capacitor C2 is connected to the internal comparators through the 2nd and 6th pins of the 555. The output is taken from the 3rd pin of the IC.Select the modulating frequency of 36 to 38 KHz and assemble it on a veroboard. After that, enclose it in a proper cabinet.

IR Receiver Cum Control Unit

The circuit diagram of an infrared receiver cum control unit is shown below. The front end of this circuit is integrated with the infrared receiver module TK1836. This TK1836 module can demodulate 36 KHz to produce an active and similar low output. The modulated IR beam from the transmitter section is received by the receiver module and its output at the pin 2 goes low. When the circuit is in sleep mode, it does not get power for its operation. So, here SCR works as an electronic switch.

When the IR beam is interrupted, then the output of the receiver module goes high and a forward bias is applied to the base of the transistor T1. As a result, the gate of theSCR gets plentyofforward bias to perform. A astable multivibrator is built around the IC1 to control the ON/OFF relay timings. The diode D1stops the relay and diode D2 works as a relaxed diode.

Normally open contacts of the relay are used to close the page button contacts until the circuit is reset by pressing push-to-off switch S1. So, to avoid its unauthorized operation, you may replace switch S1 with a key-lock. The astable circuit helps the handset user to distinguish between a normal call and an interruption warning alarm.

After completion of assembling the circuit, attach the transmitter and receiver modules at the opposite sides of the door frame. The door burglar alarm which is arranged to the door is shown in the below figure. Carefully open the CLT and solder two wires to the page-button terminals with their free ends connected to the normally open contacts. Now your cordless burglar alarm with a wireless monitoring range of about 500 meters (actual range is based on the CLT’s paging range) is ready to detect an intruder.

For a better understanding of this concept,the following project demonstrates the practical aspects of a burglar alarm sensor. This system performs automatic dialing to any telephone line by using a I2C Protocol on detecting burglary.

Automatic Dialing to any Telephone Using I2C Protocol on Detecting Burglary

In present days crime rate is increasing day by day.To overcome such a menace, this particular project has an automatic dialing provision, which helps in connecting to any telephone line using a I2C protocol on detecting burglary. The main intention of this project is to intimate the concerned authorities about an illegal access to secured areas like houses, banks, museums, etc.

Hardware Requirements

8051 microcontroller, EEPROM, DTMF encoder IC, LCD, Resistors, Capacitors, Diodes, Transformer, Voltage Regulator, Crystal, LED,
Relay, Transistors, Matrix Keypad, Push Buttons.

Software Requirements

Keil Compiler, Embedded C or Assembly

Project Description

This proposed system guarantees that at any moment if any unauthorized person tries to open the bank locker– automatically, a telephone number will be dialed through the telephone line attached with that locker.

This project uses a microcontroller which is from the 8051 family and has an external memory EEPROM, which is interfaced to the microcontroller to store the contact number to which the call has to be made. When a person tries to open the door forcefully when it is closed or locked, then the microcontroller gets an interrupt via a hidden switch mechanism which is interfaced to it.

Then, the microcontroller will automatically dial the number stored in the EEPROM through a DTMF encoder interfaced to it. The microcontroller gets the information from the EEPROM by using a I2C protocol.

Furthermore, this burglar alarm system for homes can also be enhanced by using a GSM modem or cell phone and interfacing it with a serial camera. The camera will take pictures and send it to the concerned authorities through an email or MMS for an immediate and timely action.

Thus, this is all about theLong-Range Cordless Burglar Alarm Circuit. For better understanding of this concept,the above practical example provides explicit information.

Photo Credits:

• IR Receiver Cum Control Unitby meedtech
• burglar alarm by rediff