Hey all,
me and my pals planned to make a project to make a home more secure.... 
we wanna include pirs,magnetic switches,shock sensors,ldrs(laser is the light source), pressure mats,gas leakage detectors, smoke detectors( with automatic water sprinklers if possible)...
and wanna send notifications to my mobile phone(via twitter or whatever other possible ways) when the alarm is set off....
and we need to enable and disable the security system using a android tab..... 8)
also.....we aren't experts at programming....
and we also want to know how to supply external power source to a sensor (like motors, pumps etc..) 
Do you want to make your home more secure, or do you want a massive project? Which is the priority? If it's security, just buy an alarm from a source like homesecuritystore.com. The cost of your sensors will dwarf the cost of the control panel in any event (unless you're planning to homebrew those as well); a good wired panel can be had for around $100.
If you really just want a project, alarm sensors are generally designed to present as normally-closed switches. When they open, the sensor is faulted (the door's open, smoke was detected, etc.). You should be able to easily connect these to your Arduino on the digital inputs.
Devices that need power (sirens, smoke alarms, PIRs, etc.) generally need 12 volts, so you won't be able to power them directly from your Arduino. However, very few devices intended for use with alarm systems draw much power at all, as alarms are designed to be able to run off battery power for > 24 hours, making low power consumption a critical design goal.
We are trying to make a project of a considerable size. We do want to home brew it atleast as much as possible. And we might want to reconsider the planning for the size(add-on's if any). Is it possible to make these systems work with external voltage source??
And can you update me on wireless control of the system? and what all type of arduino boards should I buy(other than ethernet shields)??
We are trying to make a project of a considerable size.
also.....we aren't experts at programming....
These two statements are incompatible, unless your goal is to fail.
PaulS:
We are trying to make a project of a considerable size.
also.....we aren't experts at programming....
These two statements are incompatible, unless your goal is to fail.
hey...i'm Vikash's parter in this project..... XD
both of us have descent programming skills......and we have advanced programmers and experts to back us up....the only problem is we meet them only once a week....or we have to travel a lot to meet them....
so we landed here to ask for help.... :)....
i know this project is quite difficult....but we're ready to work and learn.....
but we're ready to work and learn.....
Let's start with this, then. One period is enough. Three indicate that the rest of the sentence was omitted because it went without saying. Five periods don't mean anything.
One does not build a big project. One assembles a big project from small projects. Powering and reading a PIR sensor is a small project. Wiring and reading a magnetic switch is a small project. Wiring and reading pressure mats is a small project. Ditto for gas sensors, smoke detectors, etc.
Flashing and LED when a condition warrants is a small project. Triggering a water sprinkler system is a small project.
Get each of these small projects demonstrated, and then it becomes easier to assemble the big project. Jumping into a big project without knowing how to do the little projects is where you are setting yourselves up for failure.
When you get all the little projects working individually, you'll see that there are issues with connecting them together. There are a finite number of pins. If you have more inputs or outputs (or both) than you have pins, you need to see whether multiplexing is an option, or is a bigger or another Arduino needed. If you need another Arduino, then you have another small project - getting them to communicate.
Once you have the system working standalone, then you can internet it. That's another project. Whether it is small or large depends on the skills you have developed by that point.
Very true 
but as said by my friend we do get help,from experts, but only once in a while..
we have planned to buy 2 arduino AT mega version of the boards, and can arrange for more..
but as you said the big project is a assembly of small projects, so we will be planning to do it as you said(doing the small ones first and then integrating them)..
But will it be a viable project to do if we buy pre-assembled smoke detectors etc.. or should we build them too.(we have enough knowledge to build them), but will it be viable taking the space constraints??
we have around 2-3 months to complete the project..
VIKASH:
will it be viable taking the space constraints??
we have around 2-3 months to complete the project..
Those are questions that only you can answer: are you able to design and build the hardware within all the time, space and money constraints? Even assuming you already know enough to implement all this without further learning/research, 2-3 months does not sound like long enough to me, for a project this ambitious.
exams kept us busy for a while.....so here we are again....
we have until the second week of April next year before we can complete our project and submit a project completion report.....
big relief.. ..more time....and i believe we can complete the project by then.....
i now have a question....
is there any way to detect a breakage in the circuit using.....
like an alarm for a severed connection in one of the sensors.....
possible?????
Hello Vikash and Blade2012,
I'm new to the forum. You had a few questions in your posts, and I'm not sure if you got an answer.
- supply external power for motor, buzzer, etc: The simplest way is to use a relay (solid state or electro-mechanical). The "coil" of the relay needs to match the output voltage of the controller board (Arduino outputs). The relay "contacts" need to be rated for the voltage and current of whatever you are trying to turn off/on. You may need to use a reverse biased diode in parallel with the coil to keep it from over-voltage condition when you try to shut off the coil due to the inductance of the coil. You should not have this issue if you use solid state relays.
- Alarm an severed wiring. This is usually called "fail-safe" wiring. The simplest way is to use normally closed wiring. The sensor passes the current (the switch is closed) during normal times, and stops passing the current (the switch opens) when there is an alarm. However, if you are stuck with sensors that can only operate the other way (passes current when there is an alarm condition), then there are still ways to do this. A resistor can be put in parallel with the sensor at the sensor location. In this way, during normal (non-alarm) times, the circuit is completed through the resistor and you get a lower current in the circuit or lower voltage on the return wire. In an alarm state, the switch shorts across the resistor to allow a higher current in the curcuit or the full voltage on the return wire. On advantage in using this sort of circuit is that you actually get 3 states: alarm, not alarm, and broken circuit. Whereas the normally-closed switch only gives 2 states since the broken circuit and alarm give the same signal.
Now the next question is how to inject these signals into an Arduino controller, I suppose. I have not started to play with these controllers yet, so I don't know the specs on the inputs. But I'm sure the above will trigger enough ideas to get you started. If you have to, you can always use an op-amp comparator circuit to drive inputs by sizing the resistor correctly. So all your EE courses start to come together.