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Uni project - laptop alarm

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Tom Preston

New Member
I'm currently completing my final year project, in which I am making a wireless alarm for laptops, to help reduce laptop thefts at transport stations.

The alarm will sound when the laptop exceeds roughly 2 metres from the reciever, which will be located on the laptop owner.

There will be a transmitter located on the laptop/laptop case.

I am aware that products already exist which feature this (e.g. Trust.com), I am just wondering what type of circuitry is used inside these products, and in what way I could do a mock up model/rig which would show these features working?

Basically, I need a circuit that will alarm when a connection is lost.

The connection could be lost wirelessly if this is possible for me to do simply, or it could be so that if a voltage through a cable is lost the alarm will sound.

Any help will be greatly appreciated, and I will answer any questions to clear up any confusion I may have caused in this question!

Thanks,

Tom Preston
 

solis365

New Member
how about generating some sort of data sequence (from a microcontroller, perhaps) on the transmitter end, transmitting it, then receiving it. on the receiver end, set up a microcontroller that expects that data stream to come from the receiver. if it doesnt get it for more than, say, a half second, then the connection is broken and the alarm can sound...
 

Tom Preston

New Member
how about generating some sort of data sequence (from a microcontroller, perhaps) on the transmitter end, transmitting it, then receiving it. on the receiver end, set up a microcontroller that expects that data stream to come from the receiver. if it doesnt get it for more than, say, a half second, then the connection is broken and the alarm can sound...


Sounds perfect! My problem is that I have very little experience of building circuits of this type, and don't really know where to start with it.

How complicated would it be for me to build? And what components would I need?

Thankyou very much for your quick response
 

solis365

New Member
well if its your final year of university you should have had some sort of experience with this stuff...

it would probably be difficult to do without prior experience in electronics, this seems like a project suited to someone in an electrical or computer engineering major.


youll need to research about microcontrollers and how to program them. youll need to learn about transmitter and receiver circuits for whatever transmission protocol you decide to use, youll need to learn about wireless transmission of digital signals if you do it that way, receivers (again, digital signal receivers if you do it that way), and ways to check for errors and resend lost bits...

actually now that i think of it a digital signal probably isnt the way to go, you probably just want to transmit some very specific frequency or frequencies and if you want to look at them with a microcontroller than use ADCs and DACs or something, FFT with an FPGA to look at the freq. spectrum, if it doesnt match up for more than a half second then trip the alarm.


its a fairly complicated project, if you do it wirelessly. if you dont even know where to start, or if none of the above made sense, this project probably isnt something for you...


im not really getting the point of the project though. the laptop owner has a little buzzer somewhere on him, when the laptop goes more than 2m away from the buzzer then it sounds. but if you're only 2m away from your laptop then wouldnt you notice it being stolen? and what good will a buzzer do? by the time you turn around the thief is already running out the door.

and if you DONT do it wirelessly, then the laptop will just be attached to you by a wire, which is very impractical, and at that point you might just as well tie yourself to the laptop with a string.
 

Sceadwian

Banned
A cable break alarm is much more practical and generally useful than a wireless one. It's almost trivial to use the wire around the around a laptop safety loop as part of a buzzer circuit. The wireless ones are a lot more difficult, they rely on receivers that have very week but reliable reception patterns to whatever frequency the transmitter is sending. Also once the laptop is 2 meters away you might as well consider it lost. A break cable attached to a laptop security lanyard is almost sure to go off before the person gets out of grabbing distance, not to mention if you make it out of flexible braided steel cable it won't feel like anything other than a fabric tether, but it will most definitely stop anyone from casually stealing it.
 

solis365

New Member
still confused, if you're tethering it to a desk or your person, why bother with a cable that rings a buzzer, why not use something like... steel cabling. then they *cant* take it.

unless you mean, lock the laptop to the desk, and sound an alarm if the cable is cut. could be useful if youre in the library standing down 2 rows of books away and someone tries to cut your cable... itd still be too late...
 

Tom Preston

New Member
well if its your final year of university you should have had some sort of experience with this stuff...

it would probably be difficult to do without prior experience in electronics, this seems like a project suited to someone in an electrical or computer engineering major.


youll need to research about microcontrollers and how to program them. youll need to learn about transmitter and receiver circuits for whatever transmission protocol you decide to use, youll need to learn about wireless transmission of digital signals if you do it that way, receivers (again, digital signal receivers if you do it that way), and ways to check for errors and resend lost bits...

actually now that i think of it a digital signal probably isnt the way to go, you probably just want to transmit some very specific frequency or frequencies and if you want to look at them with a microcontroller than use ADCs and DACs or something, FFT with an FPGA to look at the freq. spectrum, if it doesnt match up for more than a half second then trip the alarm.


its a fairly complicated project, if you do it wirelessly. if you dont even know where to start, or if none of the above made sense, this project probably isnt something for you...


im not really getting the point of the project though. the laptop owner has a little buzzer somewhere on him, when the laptop goes more than 2m away from the buzzer then it sounds. but if you're only 2m away from your laptop then wouldnt you notice it being stolen? and what good will a buzzer do? by the time you turn around the thief is already running out the door.

and if you DONT do it wirelessly, then the laptop will just be attached to you by a wire, which is very impractical, and at that point you might just as well tie yourself to the laptop with a string.
My brief is to 'reduce laptop thefts at transport stations'. The reasoning behind my idea is that as transport stations are busy environments, there is a large amount of laptop thefts which occur.

The idea is that people commonly place their laptops on the floor by their side when reading timetables, sitting down at cafe's, waiting area's etc. They are then highly vulnerable to con artists and thieves who 'sneak' the laptops from underneath their noses, and by the time the laptop owner has noiced, it is too late.
This device should act as an alert, and is also going to be a visual deterrent to thieves who target the laptop.

I understand that building a wireless circuit may be too complicated, and have looked at existing products which use the wireless feature which I was hoping to use, all of which have been very unreliable and not had a significant alert which would work in busy environments.
 

colin mac

New Member
Maybe if you play around with RF modules you can come up with something that has a short enough range. RF modules have an antenna pin for attaching an antenna. I found that without adding an antenna the RX and TX can communicate if they are in the same but an antenna is needed if they are in different rooms of the house. I haven't tested the distances in open space though.
 

solis365

New Member
My brief is to 'reduce laptop thefts at transport stations'. The reasoning behind my idea is that as transport stations are busy environments, there is a large amount of laptop thefts which occur.

The idea is that people commonly place their laptops on the floor by their side when reading timetables, sitting down at cafe's, waiting area's etc. They are then highly vulnerable to con artists and thieves who 'sneak' the laptops from underneath their noses, and by the time the laptop owner has noiced, it is too late.
This device should act as an alert, and is also going to be a visual deterrent to thieves who target the laptop.

I understand that building a wireless circuit may be too complicated, and have looked at existing products which use the wireless feature which I was hoping to use, all of which have been very unreliable and not had a significant alert which would work in busy environments.
im just thinking that, in a busy environment like that, unless the laptop is physically attached to your person, if someone grabs it from your side, they can run and get lost in the crowd before you have time to even react. 2 meters in a crowd is a big headstart if they didnt notice you taking it.

put a louder buzzer on already existing products?
 

Sceadwian

Banned
The key to short range RF like that is intentionally choosing a really crappy antenna. Even then you're going to get random range depending on how the receiver and transmitter are oriented.
 
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solis365

New Member
The key to short range RF like that is intentionally choosing a really crappy antenna. Even then you're going to get random range depending on how the receiver and transmitter are oriented.
an array of really crappy antennas on each device to make sure range makes no difference?:rolleyes:
 
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Sceadwian

Banned
About 1 meter, depending on antenna type and orientation range will vary greatly.
Like I said though, if the laptop is 1 meter away when the alarm goes off, it's gone already. Car alarms work because they go off before the car is stolen, not after.
 

confounded

New Member
how about a cable break alarm or wireless signal loss alarm that when cut/activated triggers a paintbomb, then you can see who has stolen it :eek:
 

Thunderchild

New Member
another problem being if you have the receiver on you when you turn about your own body will block the signal creating random and slightly unpredictavle range, unless of course you wear the receiving antenna like a belt
 

tcmtech

Banned
Most Helpful Member
What ever happend to good old fasioned self dilegence? That is, Just dont leave your stuff lying around where someone can take it!
I travel some and nothing I have is ever further than my own arms length while I am sitting, standing, or even in the bathroom.
My bags are under my feet and my laptop is in its case on my lap. The closer people are to me the closer my stuff is to me!
 

Sceadwian

Banned
Oh no tcm we can't have that, this is America! If something could possibly go wrong there must be a product we can purchase for 19.99 to prevent it from happening.
 

tcmtech

Banned
Most Helpful Member
Doh! Stupid me I keep forgeting that just because North Dakota is still part of the united states that does not actualy mean the rest of the country thinks like we do! :rolleyes:

Sorry my bad! :p
 
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