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simple alarm system ideas?

hello. I would like to install a very simple alarm system. I've been reading a little about the professional models online and they have to many features and most have very poor documentation for a beginner.

I was thinking of something simple like magnetic contacts on all exterior doors wired to a piezo buzzer by my headboard.

I'm assuming I would use normally open contacts wired in parralell then wired in series with a piezo buzzer? Do I need resistors or anything else?

I realise the alarm would cease if the wires were cut or the door was shut but it would be enough to wake me up and hopefully startle the thief.

My other question is can those radio shack surface mount contacts be used on a steel door with foam core without using some kind of stand off? I've heard you can and cant so I dont know what I should do.

I appreciate any other ideas. im just learning about electronics so I want to keep it simple.

thanks

Reply to
Spork
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I also would be interested on how to link this system up to a computer for logging etc of movement.

thanks JJ

Reply to
Tamar Solutions

Use normally closed contacts, and invert the signal using a relay or transistor for controlling the buzzer. That way, cutting the wires sounds the alarm.

If using a relay, connect all switches in series, and one end to +line and the other to the relay coil. Connect the other end of the relay coil to -line. Connect the buzzer to the +line, and the other end to the NCcontact of the relay Connect the common of the relay to the -line.

If using the transistor, use a series resistor of say 2k2 in the base connection (6-24V circuit). Transistor can be something like a BC558 or BC337, a simple NPN-type of minimum say 100-200mA. Connect the buzzer to the +line and collector. Connect the emitter to the -line. Connect all switches in series, and one end to +line and the other to the base-resistor of the transistor.

For as well transistor as relay circuit, the buzzer voltage should be as the power supply.

Linking the system to a PC is fairly easy, using a simple off-the-shelf multi-IO board. That way, using a little programming, all circuits can be controlled individually. Most of these boards have a simple program delivered, so it's as easy as connecting and running the program.

greetz

I also would be interested on how to link this system up to a computer for logging etc of movement.

thanks JJ

Reply to
peterken

reading

features

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heard

Wire the contacts in series with a relay coil and the relay's own contacts so that when the relay drops out it can not be reset until you reset it. You would need a relay with two contacts. SPDT (single pole double throw) The coil voltage should match your supply voltage. The supply should first go to the relay's common. The N.O. (normally open, the one open when the relay is not energized) goes to the relay coil. The N.C. contact goes to the sounding device. The trip contacts are in series with the relay coil. You have to manually arm the alarm. Put a N.O. push button switch between the relay common and N.O.

Regards, Tom

Reply to
Tom Biasi

Thanks - so would a PIC chip is what I would need?

Reply to
Tamar Solutions

would it be safe to use a 12 volt wall wart for this project? I was thinking I could use a louder piezo and not worry about batteries. would that be safe?

thanks

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Reply to
Spork

Sure, as long as you don't stick your tongue between the contacts. ;-)

Cheers! Rich

Reply to
Rich Grise

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