I need a suggestion for a MOSFET(?) that controls a siren

ElectricAye

Hi everyone,

I've been asked if I can use a Propeller to monitor the doors and windows of a building and sound a siren if anyone intrudes. The siren is already in place and I have no documentation for it except what I've gained by testing it.

At 3 volts, it uses less than 0.1 amps and barely peeps.
At 5 volts, it uses about 0.2 amps and makes a decent amount of noise.
At 10 volts, it uses about 0.3 amps and knocks my socks off.

I'm guessing some kind of MOSFET would do the trick, but I've never used one and I don't know what sort of criteria to search for on Digikey's spec search.

I have one of these ixdev.ixys.com/DataSheet/99444.pdf sitting around, but I'm not sure it would be right for the job.

Any suggestions on how to approach this problem will be greatly appreciated.

Thanks,
Mark

Phil Pilgrim (PhiPi)

The MOSFET you have would be unsuitable due to its gate voltage requirements. A better choice would be an IRF3708.

-Phil

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ElectricAye

Phil,

Awesome, man! Your suggestion looks great.

Thanks!

Mark

mcstar

With that mosfet, you should be able to drive the gate with a prop pin, although I'd probably at least buffer it with a 1k resistor just in case.
Tie the + of the siren to your 10V power and the - of the siren to the drain of the FET. Then tie the source on the Fet to a common ground with the prop's power.

ElectricAye

McStar,

thanks for the tip on using a 1K resistor to buffer the output of the Propeller pin. I often forget: even if the component doesn't short out the pin, something else I do probably will short it sooner or later.

cheers,
Mark

mcstar

Yeah, I've driven gates directly with prop pins without a problem before, but I've also seen blown mosfets that end up with a short between gate and source! You'd hate to waste a prop just because you overloaded the mosfet during prototyping.