wire loop alarm

hi
i am making a home security system for the complete society (comprises of 300 flats). so in that system there will be some wires which will be running through the society .so i want an alarm which will turn on if someone tries to cut the wires.
what i have in my mind is that run a sepreate wire along with those wires.
so if someone will cut the wires the wire will also break and the alarm turns on.

so i think i need a wire loop break alarm.
i get some circuits from the net but they have there own llimitations that u cannot increase the length of the wire ..but in my case the legth of the wire would be atleast 500 mtrs
if anyone have a better idea or circuit.i would like to go for that one.

any suggestions

hi,

It depends upon the total resistance of the wire loop?

Which in turn depends upon the wire length, you say 500mtrs, also important is the CSA [cross sectional area] of the wire conductor.

Simply, the heavier the wire gauge the lower the resistance/metre.

Also consider the effect of a local 'electrical storm' upon the loop being connected directly into semiconductor inputs.

The induced em pulses would destroy the ic's also you could get false alarms.

Wire loops in security systems are in common use, care must be taken in the routing and termination of the loop.

Does this help?

Why not simply use a relay.

The relay is held operated via the loop; the alarm is activated if loop is opened and the relay releases.

Also note that a relay will hold with a lower current through its coil than is required to operate it. So you could have a "set" button to operate the relay and let it hold via the loop and a resistor. The resistor value would be selected so that the current is greater than the hold current. Thus you can reduce the energy consumption.

ljcox said:

Why not simply use a relay.

The relay is held operated via the loop; the alarm is activated if loop is opened and the relay releases.

Also note that a relay will hold with a lower current through its coil than is required to operate it. So you could have a "set" button to operate the relay and let it hold via the loop and a resistor. The resistor value would be selected so that the current is greater than the hold current. Thus you can reduce the energy consumption.

Click to expand...

is that what u r talking about??
if yes then can u pls give the specifications of the component used(i mean the value of the resistance capacitance 'if any' and which relay)

here is the attachment

This is what I mean.

You can use virtually any relay. Choose the supply voltage V to suit the relay.

Virtually any diode will be suitable, eg. 1N4148, 1N4004, etc.

i think both the circuits are similar. . .
i m not very much familiar with the electronics component. .
so can u tell me the specification of the relay so that i can purchase one from the market and hav a look whether it works or not.because in market u hav plenty of different relays. .so how to tell a lay man that i want this relay

mayankguru said:

i think both the circuits are similar. . .The one you attached is not a circuit, it is a wiring diagram. It does not show what A, B & C are. As far as I can see, it does not have the memory function that my suggestion has. In my circuit, if the loop is broken, the siren will sound, but if the intruder re-connects the loop, the siren will stop. If that occurs with my circuit, the siren will continue to sound until the "set" button is pressed.
i m not very much familiar with the electronics component. .
so can u tell me the specification of the relay so that i can purchase one from the market and hav a look whether it works or not.because in market u hav plenty of different relays. .so how to tell a lay man that i want this relay

Click to expand...

What supply voltage do you intend to use to power the circuit?

For example, say you want to run it from 12 Volt, then buy a 12 Volt relay with a SPDT contacts that can switch the current drawn by the siren.

Or, if you want to run it from 24 Volt, then buy a 24 Volt relay with a SPDT contacts that can switch the current drawn by the siren.

ljcox said:

What supply voltage do you intend to use to power the circuit?

For example, say you want to run it from 12 Volt, then buy a 12 Volt relay with a SPDT contacts that can switch the current drawn by the siren.

Or, if you want to run it from 24 Volt, then buy a 24 Volt relay with a SPDT contacts that can switch the current drawn by the siren.

Click to expand...

ok is there any relay which can b operated at 5volts and what about siren is the siren available in market in terms of volts only or any other specificatoin is also required for siren

and will the circuit work if i connect the component exactly as shown in the wiring diagram or naything else is also required

mayankguru said:

ok is there any relay which can b operated at 5volts and what about siren is the siren available in market in terms of volts only or any other specificatoin is also required for siren
I know nothing about what sirens are available. I suggest you research this and what voltage they operate at.

Then select a relay of the same voltage.

Yes, there are 5 Volt relays, but you need to examine the siren options first.

and will the circuit work if i connect the component exactly as shown in the wiring diagram or naything else is also required

Click to expand...

The only improvement I would make would be to buy a DPDT momentary toggle switch rather than a push button as drawn in my circuit. Then you can prevent the siren sounding when the circuit is set, ie. while the button is pressed.

ljcox said:

The only improvement I would make would be to buy a DPDT momentary toggle switch rather than a push button as drawn in my circuit. Then you can prevent the siren sounding when the circuit is set, ie. while the button is pressed.

Click to expand...

Sorry, I wrote this post in a hurry and confused myself.

What I should have written is this:-

The siren will sound when the power is turned on until the button is pressed.

You can avoid this by pressing the button before turning the power on so that the relay operates immediately.