in reply to Using Perl to make a hot-lead from any port

As simple as it is, you need an external controller for that switch that will be signalled to turn the bell on or off. Only when the controller is specified is it possible to say what the computer has to do.

If you have a custom computer supplier (instead of the usual off-the-shelf trained monkeys) , they should be able to tell you which controller to get and it will have a manual that will tell you how to operate it from the PC.

On second thoughts, because you are going to use a relay, if using unix or linux you just have to write lots of FFFF (hex) to the relevant device in /dev.

More update: I also thoroughly agree with the replies that suggest isolating the port from the bell circuit. I had an idea for isolating with a rectifier although I am scratching that because it would only (literally) half work for a/c.

-M

Free your mind

  • Comment on Re: Using Perl to make a hot-lead from any port

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Re^2: Using Perl to make a hot-lead from any port
by samizdat (Vicar) on Oct 05, 2005 at 13:06 UTC
    A diode is a semiconductor version of a rectifier, but it does not isolate the circuit against any of the nasties that lurk out there in The Real WorldTM. First off, any diode (or old-style germanium rectifier, for that matter) has a breakdown voltage, which is the point where the little bitty lectrons jump the PN junction chasm anyway, creating a closed circuit. Typically these 'reverse breakdown voltage' thresholds are on the order of 50-100v, and so either 110VAC or any level of static electricity is enough to pass a diode. The static charge generated by walking across a carpet can easily be more than 800v, although the current is rarely worth worrying about. A lightning strike nearby or any heavy rotating machinery like generators or motors can play havoc with the ground potential, though, so there are a number of very real potential trouble sources. In many of the third world countries, as in (still!) parts of the US, grounding is neither sufficient or complete, so extra care is highly recommended.
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