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Innovations In Burglar Alarms Ppt
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- 2. CONCEPT OF BURGLARALARMS: Burglar alarms have become standard equipment in stores and other businesses, and they're becoming increasingly common in private homes as well. This area is generally a road less travelled for an engineer, but it should not be so. If you've ever shopped for a home security system, then you know there are a wide variety of options available. But, most alarm systems are actually built around the same basic design concepts.
- 4. Steps involved: These things take place in a sequence. BREAKING DETECTION SOUNDING THE OF MOTION THE ALARM CIRCUIT
- 6. BREAKING THE CIRCUIT: In any circuit, to turn the electricity on or off, you open or close part of the circuit using a switch. In a burglar alarm, the switch detects the act of intrusion These sorts of alarms are divided into two categories: 1.closed-circuit system(if somebody opens the door, the circuit is opened, and electricity can't flow. This triggers an alarm) 2.open-circuit system (opening the door closes the circuit, so electricity begins to flow and the alarm is triggered) Closed circuits are normally a better choice than open circuits because an intruder can deactivate the open circuit by simply cutting the connected wires.
- 7. A BASIC MAGNETICSENSOR A magnetic sensor in a closed circuit consists of a few simple components. For the most basic design, you need: (1)a battery powering a circuit (2)a spring-driven metal switch built into a door frame (3)a magnet embedded in the door, lined up with the switch (4)a separately-powered buzzer with a relay-driven switch. This is a fairly simple circuit.
- 9. CONTROL BOX: But,the burglar only needs to close the door again to turn the buzzer off. That's why most modern burglar alarms incorporate another piece into the circuit -- the control box. The control box is hooked up to one or more alarm circuits, but it also has its own power supply. It monitors the circuits and sounds the alarm when they are closed or opened (depending on the design). But once the alarm is triggered, the control box won't cut it off until somebody enters a security code at a connected keypad. For added security, the control box is usually positioned in an out-of-the-way spot, so the intruder can't find it and attempt to destroy it.
- 11. DETECTION OF MOTION: The intruder's actions are highly unpredictable once he is inside -- you don't know where they'll go or what they'll touch. A specific "trigger" isn't very effective. To detect an intruder who's already in the house, you need a motion detector. An automatic door opener is an example of a radar-based motion detector The motion detector emits radio energy into a room and monitors the reflection pattern. Another simple design is photo-sensor motion detectors. Photo- sensors have two components: (1)a source of focused light (often a laser beam) (2)a light sensor
- 12. Passive infrared (PIR) motiondetectors •In a home security system, you aim the beam at the light sensor, across a passageway in your house. •When somebody walks between the light source and the sensor, the path of the beam is blocked briefly. •The sensor registers a drop in light levels and sends a signal to the control box. •PIR detectors are designed to trigger the alarm when infrared energy levels change very rapidly. •All these motion detector designs can be combined in a photo-sensor motion house to offer complete detectors coverage.
- 13. TIME DELAY: Ina typical security system, the control box will not sound the alarm immediately when the motion detectors are triggered. There is a short delay to give the homeowner time to enter a security code that turns the system off. If the security code is not entered, however, the control box will activate various alarms.
- 15. SOUNDING THE ALARM: In an advanced system, the control box will be wired to several different components. . Typically, it will activate: (1)A siren or other loud alarm noise (2)Flashing outdoor lights (3)A telephone auto-dialer The siren and lights serve three functions: They alert occupants and neighbors that someone has broken into the house. They drive the intruder away. They signal to police which house has been broken into. The telephone auto-dialer can: Dial the police directly, and play a pre-recorded message giving the address of the house and any other relevant information
- 17. BASIC CIRCUITRY: In this basic circuit, the alarm will be switched on under the following four different conditions: 1. When light falls on LDR1 (at the entry to the premises). 2. When light falling on LDR2 is obstructed. 3. When door switches are opened or a wire is broken. 4. When a handle is touched. (CLICK ON THE CIRCUIT FOR A HYPERLINK TO THE SLIDE CONTAINING THE CIRCUIT)
- 18. (CLICK ON THECIRCUIT FOR A HYPERLINK TO THE SLIDE CONTAINING THE CIRCUIT) The light dependent resistor LDR1 should be placed in darkness near the door lock or handle etc. If an intruder flashes his torch, its light will fall on LDR1, reducing the voltage drop across it and so also the voltage applied to trigger 1 (pin 6) of IC1. Thus transistor T2 will get forward biased and relay RL1 energize and operate the alarm. Sensitivity of LDR1 can be adjusted by varying preset VR1. LDR2 may be placed on one side of a corridor such that the beam of light from a light source always falls on it. When an intruder passes through the corridor, his shadow falls on LDR2. As a result voltage drop across LDR2 increases and pin 8 of IC1 goes low while output pin 9 of IC1 goes high Transistor T2 gets switched on and the relay operates to set the alarm. The sensitivity of LDR2 can be adjusted by varying potentiometer VR2.
- 19. (CLICK ON THECIRCUIT FOR A HYPERLINK TO THE SLIDE CONTAINING THE CIRCUIT) A long but very thin wire may be connected between the points A and B or C and D across a window or a door. If anyone cuts or breaks this wire, the alarm will be switched on as pin 8 or 6 will go low. In place of the wire between points A and B or C and D door switches can be connected. These switches should be fixed on the door in such a way that when the door is closed the switch gets closed and when the door is open the switch remains open. With the help of a wire, connect the touch point (P) with the handle of a door or some other suitable object made of conducting material. When one touches this handle or the other connected object, pin 6 of IC1 goes ‘low’. So the alarm and the relay gets switched on. Remember that the object connected to this touch point should be well insulated from ground.
- 20. DEFECTS AND REMEDIES SUJESTED: If potentiometer VR3 tapping is held more towards ground, the alarm will get switched on even without touching. =>In such a situation, the tapping should be raised. But the tapping point should not be raised too much as the touch action would then vanish. Battery backup is necessary for this circuit Relay coils produce large reverse voltage spikes =>short circuit these spikes before they can do any damage. Electric sparking in the vicinity of this circuit may cause false triggering of the circuit. =>To avoid this adjust potentiometer VR3 properly.
- 22. AN IMPROVED FORMOF INTRUDER ALARM: The Automatic Intruder Alarm uses a Cmos 4011. The 4011 has four two-input NAND gates. NAND gates only produce a low o/p if both i/p are high. The errors of the previous model have been considered and rectified along with further improvements. Part list 1x CMOS 4011 1x BC547 1x Entry buzzer 1x Relay 1x Siren Misc: diodes, resistors, capacitors, transistors, switches, etc.
- 23. (CLICK ON THECIRCUIT FOR A HYPERLINK TO THE SLIDE CONTAINING THE CIRCUIT) The working: While the alarm is off: *Sw1 holds pin 6 low. *If the loop is opened - and R1 takes pin 5 high - it will make no difference. *While SW1 holds pin 6 low - the output from gate 2 must remain high. *While Sw1 is in the off position - it keeps C2 in a discharged state. *So - when Sw1 is moved to the set position - C2 will continue to hold pin 6 low until it charges through R3 and R4. This is the Exit delay.
- 24. EXIT DELAY: Itgives the owner time to exit the area without triggering the circuit. # during this time the alarm cannot be activated. # So it's safe to open the loop and exit the building. # Once C2 has charged, the Exit Delay is finished and pin 6 is high. Now if any one enters the area(even if it is the owner himself ) it will trigger the circuit. But the user can use entry delay to stop the triggering of the alarm.
- 25. (CLICK ON THECIRCUIT FOR A HYPERLINK TO THE SLIDE CONTAINING THE CIRCUIT) When you return to the building and open the door - R1 will take Pin 5 high. *Since both gate 2 inputs are now high - pin 4 will go low. When pin 4 goes low - two things happen: # C3 charges rapidly - through R8 & D4. # pin 4 takes pins 1 & 2 low through D4. So the gate 1 output - at pin 3 - will go high. *Pin 3 does two jobs: # The first is to provide base-current for Q1 through R2. The transistor switches on - connects the negative lead of the buzzer to ground - and the buzzer sounds. #Its second job is to charge C5 through R6. C5 & R6 provide the Entry Delay. After about 30-seconds - the voltage across C5 will takes both of the gate 3 inputs high. So the gate 3 output - at pin 10 - will go low. *Pin 10 takes the inputs of gate 4 low. So the gate 4 output - at pin 11 - will go high.
- 26. (CLICK ON THECIRCUIT FOR A HYPERLINK TO THE SLIDE CONTAINING THE CIRCUIT) * Pin 11 provides base-current for Q2. The transistor connects the negative side of the relay coil to ground. So the relay energizes - and the siren sounds. *While at least one of the trigger switches remains open, the siren will continue to sound. *If the normally-closed loop is restored pin 5 will go low. Since one of its inputs is now low - the output of gate 2 will go high * Now - pin 4 is no longer holding pins 1 & 2 low. Instead, pins 1 & 2 are held low by the charge stored in C3. * They will remain low until C3 discharges through R9. As it does so - the voltage on pins 1 & 2 will rise. * After about 15-minutes - when it reaches roughly half the supply voltage - the inputs will go high. And the gate 1 output at pin 3 will go low.
- 27. (CLICK ON THECIRCUIT FOR A HYPERLINK TO THE SLIDE CONTAINING THE CIRCUIT) When pin 3 goes low - the base current to Q1 is cut off. So the transistor switches off and the Buzzer is silenced. Pin 3 also discharges C5. During the Entry Delay D2 forces C5 to charge slowly through R6. But allows C5 to discharge rapidly through R7. When C5 discharges - pin 3 takes pins 8 & 9 low - through R7 and D2. When pins 8 & 9 go low pin 10 will go high. Pin 10 takes pins 12 & 13 high So the output of gate 4 at pin 11 will go low. This cuts off the Q2 base current. So the transistor switches off - the relay drops out – and the siren is silenced.
- 29. COMPONENTS AND THEIRUSES: • without it, it would take about 30 seconds R7 and D2 for C5 to discharge • Relay coils and some Sounders produce large reverse D1, D5 and D6 voltage spikes that will damage Cmos ICs. D1, D5 & D6 short circuit these spikes before they can do any damage • They are used to create one-way paths. D4 allows a low pin 4 Rest of diodes to take pins 1 & 2 low. It also allows a low pin 4 to charge C3. But it prevents a high pin 4 from taking pins 1 & 2 high. It also prevents a high pin 4 from discharging C3. • prevents C5 from charging rapidly through R7 - instead of D2 slowly through R6. It takes about 30-seconds for a high pin 3 to charge C5 - through R6. This provides the Entry Delay
- 30. • is toreset the Entry Delay. R7 discharges C5 rapidly - R7 through D2 - into a low pin 3. Thus - the moment the alarm is switched off - the Entry Delay is reset. • When the alarm is switched off - C3 discharges rapidly - through R5, the red LED, D3 and R8. Without D3 - pins 1 & 2 would remain low until C3 D3 discharges through R9. With D3 - the moment the alarm is switched off - its reset - and ready for immediate re-use. We need to use a diode - and not a wire link - because the diode prevents Sw1 from taking pins 1 & 2 low. If Sw1 could take Pins 1 & 2 low - the alarm would activate the moment it was set • While Sw1 is in the set position - current through Red LED R5 lights the red LED. The red LED gives a visual indication that the alarm is set • The three 1k resistors are there to limit the peak current 1K RESISTORS when the capacitors charge and discharge. The value was kept low so that the capacitors would charge and discharge rapidly
- 31. DEFECT AND RECTIFICATION: The wires going to the switches on the doors, windows, etc. can act like a radio antenna. They pick up stray signals that can cause 'false alarms'. C1 is there to de-tune the wires - and short-circuit any high frequency signals to ground. C4 does a similar job for the supply. The errors are to be rectified carefully.
- 32. ALTERNATE OPTIONS: There’snothing special about the BC547s. Any small NPN transistors with a gain (hfe) greater than 100 and an Ic (max) of at least 100mA should do. But remember that the pin configuration of your transistors may be different from that of the BC547.
- 33. CONCLUSION: Home securityis a rapidly growing field, and there are new and improved burglar alarms popping up all the time. With rapid advancement of technology the field is turning out to be an area full of scope. Even these circuits may develop faults as time goes and new changes can be made to make them more efficient. Home security is a field that can never be ignored by the engineers as it does have scope for years to come, because security is of prime importance to one and all.
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