audio transducers

[Jamie Morken]

Hi all,

I am looking for a small surface mount piezo buzzer and was wondering if
anyone has any links to one that is smaller than ~8mm diameter? Digikey has
some with these labels:

"piezo ceramic audio transducers - external drive type"
"magnetic audio transducers - external drive type"
"piezo ceramic audio transducers - self drive type with feedback"

I guess the magnetic one is just a magnetic speaker that requires AC to
drive it?
I'm not sure what the difference between external drive and self drive is,
but the self drive/feedback ones seem to have 3 pins. I would like to find
a buzzer that I can drive at 3.3V/5V at 20mA max from a microcontroller pin.
Is there a type of buzzer that can be PWM'd from a microcontroller pin to
give a varying output tone too? Thanks for any tips,

cheers,
Jamie Morken

 

[John Hall]

On Thu, 25 Mar 2004 02:35:34 GMT, "Jamie Morken"
<truespace1@hotmail.com> wrote:

Hi all,

I am looking for a small surface mount piezo buzzer...

They aren't ceramic/piezo, but there is now another option in audio
transducers, Google for ' terfenol ' (Magnetostrictive, but much more
so than earlier materials).

--
John W Hall <wweexxsseessssaa@telus.net>
Cochrane, Alberta, Canada.
"Helping People Prosper in the Information Age"

 

[Active8]

On Thu, 25 Mar 2004 02:35:34 GMT, Jamie Morken wrote:

Hi all,

I am looking for a small surface mount piezo buzzer and was wondering if
anyone has any links to one that is smaller than ~8mm diameter? Digikey has
some with these labels:

"piezo ceramic audio transducers - external drive type"
"magnetic audio transducers - external drive type"
"piezo ceramic audio transducers - self drive type with feedback"

I guess the magnetic one is just a magnetic speaker that requires AC to
drive it?
I'm not sure what the difference between external drive and self drive is,
but the self drive/feedback ones seem to have 3 pins. I would like to find
a buzzer that I can drive at 3.3V/5V at 20mA max from a microcontroller pin.
Is there a type of buzzer that can be PWM'd from a microcontroller pin to
give a varying output tone too? Thanks for any tips,

cheers,
Jamie Morken

Get yourself registered a www.piclist.com There was a bunch of
discussion about piezo sounders and driving them with PICs, so do an
archive search.

--
Best Regards,
Mike

 

[CFoley1064]

Subject: audio transducers
From: "Jamie Morken" truespace1@hotmail.com
Date: 3/24/2004 8:35 PM Central Standard Time
Message-id: <Wzr8c.901962$X%5.766765@pd7tw2no

Hi all,

I am looking for a small surface mount piezo buzzer and was wondering if
anyone has any links to one that is smaller than ~8mm diameter? Digikey has
some with these labels:

"piezo ceramic audio transducers - external drive type"
"magnetic audio transducers - external drive type"
"piezo ceramic audio transducers - self drive type with feedback"

I guess the magnetic one is just a magnetic speaker that requires AC to
drive it?
I'm not sure what the difference between external drive and self drive is,
but the self drive/feedback ones seem to have 3 pins. I would like to find
a buzzer that I can drive at 3.3V/5V at 20mA max from a microcontroller pin.
Is there a type of buzzer that can be PWM'd from a microcontroller pin to
give a varying output tone too? Thanks for any tips,

cheers,
Jamie Morken

Hi, Jaimie. Piezo transducers can be modelled as capacitors that will flex
depending on the voltage applied to them. If you apply an AC voltage at audio
frequency, you will get sound at that frequency. Generally, the louder the
transducer, the higher the capacitance. Actually, that makes sense, because
the audio power output is proportional to the power input, and a larger
capacitor takes more power to drive at a given frequency.

For external drive types, you need a "bridge driver" setup to apply an AC
waveform to the transducer. That would require something like this (view in
fixed font or M$ Notepad):

External Drive Piezo Transducer
BZ1

3KHz |\ || /|
o--| >O--o---||---O< |--.
| |/ || \| |
| |
| |
| |
| |\ |
'-----------| >O--------'
|/

You generally can't do something like this with a standard inverter. It
doesn't have enough drive capability, and reliability will be poor. You want
to use an IC that has high drive capability. Drive this with a square wave --
you change the tone by changing the frequency.

Unfortunately, the "self-drive type with feedback" isn't self-driving -- it
requires an external transistor and possibly one or two other resistors (see p.
1049 of the D-K catalog for one example). If you add the external components
specified by the manufacturer, it will oscillate by itself (self-drive) at near
the frequency specified by the manufacturer. The exact configuration of
external components depends on the manufacturer. Look at the manufacturers'
catalogs. They'll give you applications and advice.

Good luck
Chris