Ideas for a siren?

Walt&Andy

We've designed a proximity alarm based on the board of education/BS2. Waiting on PIR sensor to arrive, but feel pretty good about that portion (ignorance is bliss). In the meantime, we need to bump up from the little piezo speaker from Parallax to something that has some volume (or learn how to get more out of the piezo speaker? the online listing says it's 80db, but to my ears we're not getting anything near that). We'd like volume similar to a smoke alarm - in fact, scrapped an old alarm and are trying to figure it out, but unsure what to do with the 3rd pin on that alarm.

Thoughts? Requirements are volume, 9v, BoE compatible.

Thanks for any help!
Walt and Andy

ajward

There was a recent thread on this subject... possibly what you're looking for.
http://forums.parallax.com/showthread.php/75707-How-to-Amplifying-a-Piezo-Speaker-and-Volume-Control?highlight=piezo

Amanda

Tracy Allen

The horn from a smoke alarm is not suitable for use with the BASIC Stamp. It is meant to be used in a self-oscillating circuit. The third electrode provides feedback. Besides that, the horn provides a strong resonance at a single tone. Devices that give a single sharp resonance will always be louder than one that has to cover a broadband range of frequencies. Is that what you want? Are you driving your piezo with FREQOUT from the Stamp? There will be a narrow range of frequencies that you can find that will be the loudest and you'll have best results if you can operate it within that range.

Circuit of an ionization smoke detector, piezo at lower right...

xanadu

The two loudest I know of that are easy to acquire are:

http://www.velleman.eu/products/view/?country=be&lang=en&id=338493 (can be found locally at stores like Fry's)

http://www.ebay.com/itm/like/190848290444?lpid=82 (can also be found in local RC hobby shops)

Both require voltage only, and have a fixed tone.

bsjohn

You can use a simple IRF510 or 511 Mosfet to drive your piezo speaker. Pin out to Gate, Source to Ground, One side of speaker to 5v the other to drain. It will be very loud, just tried it!

This is not my original idea, it's from "The Microcontroller Application Cookbook" M. Gilliland

SRLM

Various places sell single tone alarms. Electronic Goldmine has this one: http://www.goldmine-elec-products.com/prodinfo.asp?number=G18223 You just apply voltage (via a relay, preferably) and off it goes. If you browse around you can find alarms in different frequency and body styles.

erco

I use a lot of these tiny self-contained piezo beepers in various projects. Just give 'em 5VDC and they give a LOUD beep. You don't send a FREQOUT or audio tone, just a steady DC signal, or of course you can pulse it for a beep beep sound. OK to drive right off of a microcontroller I/O pin. Not bad for 18 cents each. I'll have to test on 3.3V for Prop users, but prolly
ok since it says 3.5-5V.

http://www.ebay.com/itm/New-Arrival-Applied-Industrial-10-Pcs-5v-Active-Buzzer-Continous-Black-Color-Hot/370951312115?_trksid=p2047675.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%2 6asc%3D18775%26meid%3D3421752418637243712%26pid%3D 100005%26prg%3D8532%26rk%3D4%26rkt%3D4%26sd%3D3010 21506088%26

This is the same beeper I used for a super brief beep in the demo below. I left the "remove after washing" sticker on to quiet it down. Without the sticker, it is surprisingly loud.