This is door touch alarm use for your home security purpose. The alarm will be activated when someone touch the metal door or door knob. This circuit won’t work on full metal door.
Sourch
Sourch
Showing posts with label security. Show all posts
Showing posts with label security. Show all posts
Tuesday, July 20, 2010
Safe and Security System Alarm circuit diagram
This security system is very important for any kinds of home , office , factor. there has a circuit diagram its simple and easy to build . Any one can do it. It's a low cost circuit diagram.
Many security systems use a closed loop of wires and switches arranged so that whenever a door or window is opened, the loop will be broken and the alarm will sound. An obvious problem is that someone can tamper with the system, short out the loop, and later on, come back and burglarize the premises without sounding the alarm. Hiding a known resistance in the loop, as you propose, is a very good idea. That way, the alarm can distinguish a short circuit from a correctly functioning closed loop.
Figure 1 shows a circuit that does the job. It’s a somewhat unusual application of a National Semiconductor LM3915 IC, normally used to drive LED’ bar-graph displays. That chip happens to contain the right combination of comparators and logic circuits to do what you need.
Step 1 is to translate the loop resistance into a voltage; that’s done by putting it into a voltage divider with resistors R1 and R2. Capacitor C2 protects the circuit against electromagnetic noise-important because burglar alarms use long wires, often running near heavy electrical equipment.
Step 2 is to translate the voltage into a logic signal indicating whether it’s in resist-he correct range. That’s where the LM3915 comes in. Normally, the LM3 9 15 would drive ten LED's, one for each of ten small ranges of voltage. To obtain logic-level outputs, we have it driving 1K resistors instead of LEDs. Since we only need to distinguish three situations, not ten, we tie some of the outputs together. The LM3915 has open-collector outputs that can be paralleled in that way.
The truth table in Fig. 2shows how the outputs work.
Note that they use negative logic (OV for “yes”, +5V for “no”), the opposite of ordinary logic circuits. You can use inverters such as the 74HC04 to produce positive logic signals if that’s what you need.
Finally, note that the circuit will actually work with any supply voltage from 3 to 25 volts. Of course, if the supply isn’t 5 volts, the outputs will not be compatible with j-volt logic circuits.
Sourch
Many security systems use a closed loop of wires and switches arranged so that whenever a door or window is opened, the loop will be broken and the alarm will sound. An obvious problem is that someone can tamper with the system, short out the loop, and later on, come back and burglarize the premises without sounding the alarm. Hiding a known resistance in the loop, as you propose, is a very good idea. That way, the alarm can distinguish a short circuit from a correctly functioning closed loop.
Figure 1 shows a circuit that does the job. It’s a somewhat unusual application of a National Semiconductor LM3915 IC, normally used to drive LED’ bar-graph displays. That chip happens to contain the right combination of comparators and logic circuits to do what you need.
Step 1 is to translate the loop resistance into a voltage; that’s done by putting it into a voltage divider with resistors R1 and R2. Capacitor C2 protects the circuit against electromagnetic noise-important because burglar alarms use long wires, often running near heavy electrical equipment.
Step 2 is to translate the voltage into a logic signal indicating whether it’s in resist-he correct range. That’s where the LM3915 comes in. Normally, the LM3 9 15 would drive ten LED's, one for each of ten small ranges of voltage. To obtain logic-level outputs, we have it driving 1K resistors instead of LEDs. Since we only need to distinguish three situations, not ten, we tie some of the outputs together. The LM3915 has open-collector outputs that can be paralleled in that way.
The truth table in Fig. 2shows how the outputs work.
Note that they use negative logic (OV for “yes”, +5V for “no”), the opposite of ordinary logic circuits. You can use inverters such as the 74HC04 to produce positive logic signals if that’s what you need.
Finally, note that the circuit will actually work with any supply voltage from 3 to 25 volts. Of course, if the supply isn’t 5 volts, the outputs will not be compatible with j-volt logic circuits.
Sourch
Luggage Security System
There is a simple Luggage security circurit diagram by using IC UM3561 . Its Low-cost but very effective . Many place we can use this circuit like car security, Motorbike security bicycle security , hand bag etc.
So Let go to make this project.
Parts List:
Resistor:
R1 ----------------------- 10 K
R2 ----------------------- 560 ohm
R3 ----------------------- 220 K
Transistor:
T1 ------------------------ BC558
T2 ------------------------ BC548
T3 ------------------------ BC548
Integrated circuit:
IC ------------------------- UM3561
Speaker ---------------- 8 ohm, 250mW
Battry ------------------- 3V
Circuit designed by : Dhurajati Sinha
So Let go to make this project.
Parts List:
Resistor:
R1 ----------------------- 10 K
R2 ----------------------- 560 ohm
R3 ----------------------- 220 K
Transistor:
T1 ------------------------ BC558
T2 ------------------------ BC548
T3 ------------------------ BC548
Integrated circuit:
IC ------------------------- UM3561
Speaker ---------------- 8 ohm, 250mW
Battry ------------------- 3V
Circuit designed by : Dhurajati Sinha