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The device is supposed to beep loudly if the network is down, a particular port on an Internet host doesn't respond or a socket connection is made on a specific local port. Is an Arduino Ethernet shield enough? I am guessing i will also need an Arduino board and software? Are there non-Arduino solutions that are cheaper or easier to code for? This will never leave the working prototype stage.

I am a total newbie when it comes to electronics, so I am looking for a kit that covers all the hardware/software needs, excluding the speaker itself.

thanks in advance

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    \$\begingroup\$ can you comment on this requirement a bit more? "a socket connection is made on a specific local port" What is the host machine in this case? \$\endgroup\$ – Jon L May 19 '11 at 22:54
  • \$\begingroup\$ localhost. that is, i want to be able to trigger the alarm remotely from another machine on the network if needed. \$\endgroup\$ – Generic Person May 21 '11 at 13:02
  • \$\begingroup\$ I see. That shouldn't require anything special then, as long as the localhost in this case can open a connection with the monitoring device. \$\endgroup\$ – Jon L May 21 '11 at 17:01
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This should have been a comment, but I fear it's too big for comment field.

A major part of the design can be the speaker, so you should pay considerable attention to that.

There are several options you could use and the best depends on the type of sound you want to achieve.

I'll first talk about the easiest option to set up. That would be a self-oscillating buzzer. In this question I got some nice answers on how to connect one to an AVR microcontroller (of same family as ones used in Arduino). The downside of this is that the buzzer produces only one frequency and all you can do is turn it on or off. On the other hand for a simple alarm, it should probably be good enough. The plus side is alto that you can only turn it on or off. This makes it very easy to program the microcontroller. The buzzer shouldn't be too expensive. The price will of course depend on the size and power, but for this type of application, 2€ or 3€ would be more than enough for the speaker and the transistor needed to drive it.

The second option is to use a piezoelectric sound source. The downside of them is that you must create your own driving circuit for the speaker. You could make an oscillator or you could use the Arduino to create square waves and then using a transistor and a resistor drive the sound source. I don't know how much this would cost.

Another option is to use a real speaker. The easiest way to do this is to get a cheap amplifier chip and connect it to the speaker. You'd also need electronics for the amplifier (but that could be just a couple capacitors for some amplifiers). Another problem is that you'd need to use the Arduino to generate audio signal which will drive the amplifier, making the programming a bit more complicated. A positive side is that you can (with right amplifier choice) easily control volume. expect high price. The speaker could easily cost couple of Euros and so could the amplifier.

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  • \$\begingroup\$ Thanks for this answer -- i am picking it as best because the speaker is the part of the project i am less familiar with. All other answer are very welcomed, though. I will now spend sometime researching all the options; i am a bit intrigued by the bifferboard because it's x86. \$\endgroup\$ – Generic Person May 21 '11 at 13:07
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The hardware you suggested sounds right for the job, given your skill level as well. Are there non-arduino solutions? Yes. Would they be easier to code on? Probably not. Given that this is your first venture into electronics, I highly recommend the route that you've already suggested.

You will need the arduino board as well. That is where your program will go. The ethernet shield is an add on peripheral. The software to write the programs ("sketches") is free as well.

Happy hacking! http://www.arduino.cc/en/Reference/Ethernet

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Once you stack a communications shield on an arduino, you generally lose the cost advantage over a different micro with that peripheral (ethernet, usb, whatever) built in. And you can't quite fully leverage the peripheral since it's comparatively "at arms length" from the processor core.

But it obviously does work for many purposes, and lets you stay in the same software environment if you are familiar with that.

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Another good low-cost option is the mbed. It comes with an ethernet controller on-board, as well as a bunch of other bells and whistles. It is ARM based, so quite a bit beefier than the AVR on the arduino.

You will need to add an RJ45 magjack though.

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I would hack some USB ready linux router. It has all the hardware you need if you add USB sound card and loud speakers to it. The other way would be to make sirene electronics triggered by some digital output pin from router.

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  • \$\begingroup\$ Indeed I am now looking at a solution based on a bifferboard; total cost for this project should be lower and it can probably host some other services too. Thanks! \$\endgroup\$ – Generic Person May 21 '11 at 13:08

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