Re: Noob piezo resonator question:
- From: Nemo <Paul@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
- Date: Wed, 3 Oct 2007 22:18:43 +0100
Sorry to be such a novice, but can someone tell me if a piezo electric
crystal resonator will make an audible sound
if I hook it up to a small battery?
I'm looking for any miniature lightweight electronic sound generating object
for a miniature toy I'm developing.
I have small transducers that work well, but I'd like to go smaller and
someone said piezo crystals are what they use
to make watches beep, etc.
Thanks in advance.
P.S.
I've seen some the specs for which mention 1.8 mhz to 50 mhz as the
frequency range, but I'm guessing
all of the above will be inaudible(?)
You are on the right track but you have a number of half truths which are misleading you. Here's the rest of the story.
Piezo devices come in all kinds of frequencies from audio (sub 20kHz) through ultrasonic (60kHz is the kind of freq they used to be for things like position sensors) to MHz these days (not sure what they use those for, probably all kinds of things). Anyhow, you want the audio frequency ones. You can find these in various catalogues like Digikey under headings like "piezo sounders".
There ARE a few with a circuit built in which just need a battery attached but most need an oscillator attached. For the loudest output, one which resonates at the resonant freq of the piezo element as it flexes. Piezo devices usually have a fairly sharp resonance so are good for high pitched beeps but not for speech reproduction (speech is generally below, um, 4kHz I think and piezos only really start making appreciable volume at 2 - 4kHz). Although for very small air volumes like inside your ears, piezos can produce a better range of sounds - don't ask me why - which is why iPod earpieces use them.
The two main sounder technologies (for small items anyhow) are piezo and electromagnetic (coil). Coil sounds better for audio but is only about 2-5% efficient so for battery operated things piezo is often used - a massive 10% efficiency, = longer battery life. Piezo usually needs 2-4 times as many volts to give te same volume as coil, but because it needs less current it's less power overall. For a battery operated toy, piezo is probably cheaper and will definitely give you more battery life.
What you need is an example circuit here, but I've run out of time. Um... try googling "piezo circuit", this gives you various example pages.
Oh one other thing. Piezo elements are sometimes sound as bare disks. Don't buy them unless you know what you're doing as you then need to build a cavity round them and somehow attach wires. For your first piezo circuit, at least, go for one with a plastic moulded case and 2 actual pins or leads. Some have 3 pins, which use a different circuit to drive them.
.
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