System House Alarm
a house has a burglar Alarm system. describe the hardware and processing involved in such system?
a hardware like Pressure sensor or light sensors, describe the hardware and processing involved in such system?
It usually isn't that complicated.
There are a bunch of inputs;
they are connected to a central junction / relay/ computer? ;
they have one or more outputs.
Inputs:
pressure sensors are widely available for a variety of applications. You would want one in the likely path of an intruder, it should be disguised or under something, and it should be ranged (by default - or by adjustment) to ignore the 7Lb cat or 25 Lb dog.. but go active with greater pressures. Remember to compensate for minor deviations from atmospheric pressure and thermal expansion of your mounting surface(s)
Light sensors - again, a wide range of application, from lasers to infra-red and visible light.. which could just detect heat from an intruder, or detect a fault when a beam of light is broken.
Ultrasound is also used - that detects motion in front of the detector, and you choose how much ( size of target, amount of motion) is a good threshold.
Most alarm systems work on much simpler contacts -
on a window or door frame, there is a small current passed through a sensor. A mating surface ( the door or window) a small magnet is mounted. As long as the magnet is there, the switch inside the sensor is help open. Move the magnet ( open the door or window) and the switch closes, causing a circuit change.
-or a pressure switch.. a spring loaded cylinder with a switch inside is mounted in the frame. As long as the door or window is closed, there is no current passing. As soon as the device is opened, the cylinder is able to expand, and - circuit trips.
... these all take some planning, for location, sensitivity, and service-ablility (how do you replace or fix them.. without making them easy to defeat).
In a better alarm system, these are applied in layers. An external sensor detects a possible intruder, then an open door or window trips a circuit, and inside there are pressure or sonic sensors. If one fails - or is fooled - the others work.
Of course, there needs to be a way for valid users to identify themselves.. a key, a numeric pad, etc.
Processing - as simple as possible. Usually just " If any of these wires goes high, that means to send a signal to output"
You might have a time delay here to allow for a valid id.
You may have different outputs for different inputs.
Output:
send a signal to a loud alarm (or 'silent'), send a signal to turn on emergency lights;
send a signal to a monitoring station, or your cellphone, or to the police
send a signal to any defensive devices - smoke machine, lock all the doors to keep intruder trapped, set off a painful 130dB + siren, electrically charge surfaces to give a shock to intruder; set off the " Step away from the car!" recording.
You may need a backup battery to maintain power, and you probably want a telephone line if this is a residential alarm.
