Making piezo louder

it seems to be impossible what I want :/

You need to tackle the problem more systematically. I'd suggest starting by connecting an oscillator to the piezo to find out first of all exactly how many volts ( and milliamps ) drive are required.

Graham

That is probably quite loud !

How big is the piezo ? Do you a model number - link to a datasheet etc.

Graham

no I do not have any datasheet it has 24mm

And have you tried an oscillator driving it ( and measured the current ).

Graham

For what you seem to need the piezo for, why not consider an led at the edge of the helmet to alert you, instead of sound. As like you said about background noise on a motorcycle going down the road. ??

i did not connect an scope couse i have none :( I`ve build and altimeter for parachuters and it needs to signal specified altitiudes with sound, it can not be led becouse it is placed near ear...the falling speed is b

bout 50m/s and belive me it is very noise in there ...

funny but i couldn`t find any datasheet ..

Why don't you try to find a datasheet for a similar part? That will at least give you a starting point.

Best regards, Spehro Pefhany

Here is a start for you... post a picture of the device you are using.

In that case, you don't want to amplify the beeper - you need to install foam sound insulation around your ears; then you'll be able to hear it just fine just the way it is.

Good Luck! Rich

... but don't lose sight of the fact that, with the NPN buffer, it won't work at all without the inductor (no DC path). Maybe instead connect from AVR through inductor to piezo to ground (assuming the AVR's protection diodes are OK)? With this arrangement, the piezo voltage can exceed the supply by many times if driven at resonance, but it will still work well at any lower frequency.

But the other important thing is the acoustic loading on the piezo. Most loud piezo alarms also have a cavity in front of the piezo, and the self-oscillating circuit uses the resultant acoustic resonance (reflected as an electrical impedance) in order to oscillate, thus keeping both acoustic and electrical systemes near resonance, and thus working efficiently. It would be very hard to achieve anything like this when generating the signal in an AVR.

Tony

The size of the hole in the cavity is important. A simple open-ended tube probably has too low a Q.

Best regards, Spehro Pefhany

in

It's certainly more convenient (and more compact) to use a conventional closed resonant cavity with a hole in it, but I would expect a plain open-ended quarter-wave tube to work at least as well, maybe better (larger volume should make the exit impedance match the air better).

Regards, Tony

in

But he says it does work which suggests to me that maybe there's something here that he hasn't mentioned.

Graham

From reading the whole thread I finally got enough information to hazard an opinion.

Go find the watch you took the piezo and inductor out of and put the piezo back in (I'll assume it came from the back of the case, which is usually where they are). Back it up with something with audio properties similar to the watch guts (you're basically using the "speaker enclosure" designed around the piezo by the watch manufacturer, and since they did all that work, you might as well take advantage of it) and install the inductor appropriately.

Then figure out what the original driving signal looked like and duplicate that as closely as you can with the microcontroller. Mount the piezo+"enclosure" in whatever piece of headgear you are gonna use for skydiving. Test it on the ground first, because it'll likely be _too_ loud. Remember that watch alarms are meant to be unmistakably heard from arm's length but you'll be putting it right next to your ear.

If the rest of the watch isn't available/doesn't work, go buy a WalMart or similar cheapo (I wouldn't spend the time designing what you want for that for the six bucks or so the watch will cost) for parts and do as above.

Mark L. Fergerson

Sorry to be late to the party.

To make the piezo louder, you want more voltage across it--so the inductor goes in series, not in parallel.

Cheers,

Phil Hobbs

^^^^^^

Yeah, well, I believe the OP has wandered off...

I completely missed that he said "across" above. I shoulda said "as originally used" of course.

I just couldn't see why he wanted to reinvent the wheel and then wanted help figuring out where the axle goes. ;>)

Mark L. Fergerson