Ideas needed for wireless DIY project

Hi everybody,
I'm faced with a minor problem, for which I'd like to create a simple, cheap DIY solution.
There are two rooms in the house, the first one holds an electrical device (a computer) which switches itself off after a given amount of time. In the second room, I spend most of my time. I'd like to be notified if and when the computer has been switched off.
There are some problems so far: - I do not have a wireless network, nor am I planning on setting one up, so I can't check the network. - I can't hear the computer in the other room, so that's not a solution - I'm just too lazy to run over to the other room every now and then, and if I weren't, well, I wouldn't have a little DIY project to dabble with ;)
Basically I'm looking at a small, cheap project to wet my hands in electronics. I was thinking along the lines of: - pulling 12V from a USB cable from the computer - the USB cable powers a cheap transmitter (think RC cars) - in the other room is the receiver, which activates a LED as long as a signal comes through - if the PC shuts down, USB no longer is powered, transmitter stops, and the LED goes dark.
Another idea was using a magnet, and a magnetic switch on the other side of the wall, but that would have to be one strong magnet I guess :)
Any other ideas? Preferably without drilling through the walls?
Thanks in advance!
Ikke
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wrote:

It's 5v from the USB, not 12v (not that that makes much difference for what you want to do) and on modern computers, this is normally available all the time unless the computer is physically unplugged / switched off at the mains. (When you turn the PC off, it just goes into standby).
Wouldn't a simpler thing be to just take a 12v connection (I think the 12v is switched off when the PC is off) via a spare socket in the PC and run it via a cable to the room you're in?. The wire needn't be very thick and so should tuck away under carpets etc. You could then use the 12v to control whatever you want, even a simple LED indicator. That's probably what I'd do in similar circumstances.
Roger
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If you wanted a wireless option, one way might be to use a cheap wireless bell - the sort that has the wireless bell push outside the house. The bell push is powered by a battery, so you could replace that with a 12v feed from the PC (you would probably have to have a regulator circuit to adjust the voltage to the same as the battery (9v?). The actual push switch could be shorted out so that it is permanently on. As long as the 12v is present, the bell push will be transmitting a signal to the bell.
For the receiver, at the "bell" (for want of a better description of the receiver) the bell circuit could be modified to light an LED instead of making a sound. Some bells have a LED that lights when the bell sounds, so that may save you a job. Depending on the receiver battery life, you may need to fit a power supply to that as well.
The disadvantage to using a transmitter in this way is that you are transmitting a signal as long as the PC is on and the signal may interfere with other equipment (such as remote controls, other wireless equipment, etc. or Wi-Fi) in your or a neighbours premises, whereas the brief couple of second signal transmission that you get when you press the bell push probably wouldn't have any effect.
Roger
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<snip>

Nice idea, I guess I'll have to try it with our local radio stations over here :)
Anyway, thanks everybody for your ideas! I think perhaps the combination of Romic & Rick's ideas is the best solution for me, some kind of device based on a wireless doorbell.
Thanks again!
Ikke
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The beauty of Romic's wireless door bell idea is that even ones with an 'alleged' 100 metre range can be picked up for next to nothing (*under 10.00 in the UK) I'm thinking that you could maybe even get away with something as simple as an R/C circuit, which could be made to activate the contacts of a miniature relay for the duration of a few seconds after the loss of voltage from the USB, there used to be a number of electronics magazines on sale with dozens of simple little circuit ideas, which alas nowadays appear to be very few and far between. *<(Amazon.com product link shortened)00999263&sr=8-2>

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Why not just set the computer not to switch itself off?
Alternatively, you could think about a network over the mains, but, although I've never tried it so cannot comment from experience, ISTR that can sometimes be unpopular with your neighbours.

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<snip>
I've done that already, but sometimes the computer fails to turn off (it only turns itself off when the software exits correctly) so it keeps running all night.
Thanks though,
Ikke
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Put a spokey-dokey in the PC fan :)
Why would you want to know if the PC turns off? If it's set to go into standby after x minutes, then you can set a timer on your watch or phone to go off after the same number of minutes, and arm it when you finish using the PC. There might be a simple solution if you said what the computer is used for, and why you need to know if it's turned itself off. If you're doing it as a little project to get some experience with electronics, ignore the above...
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<snip>

Ehrm... I have absolutely no idea what a spokey-dokey is, and a quick Google has me believe it's some kind of harmonica?

Well, there are two reasons. First of all, I'm running a lot of calculations on my PC, and the PC should stop running as soon as they're done. So I wrote a little piece of software to shut down the PC when my main software ends.
Unfortunately, due to the nature of the calculations (and lots & lots of faulty data to sift through), my software sometimes enters a state where it cannot exit. An error, yes, but an inconvenient one: it holds up further calculations, and my PC keeps running for several hours until I can turn it off or fix the problem. Hence the need to be notified - I know roughly how long the process will take, so if I still see blinking lights or hear a bell (you get the picture), I can take action myself.
The second reason is, indeed, to get some more experience with electronics. I'm a software developer, know a lot about hardware, but I know next to nothing about electronics.
I'd like to learn more about the latter, and perhaps one day combine the two.
Thanks for your input!
Ikke
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Wouldn't it be a much simpler idea to setup the software in the computer so that it does not shut down at all..... ?
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