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'[EE] Piezo buzzers'
2005\09\07@214850 by Jinx

face picon face
> Two-tone ?

You won't get two-tone sound from a single piezo that has its own
driver. That driver is already (probably) optimised for the resonant
frequency of the element. You would have to switch one of the
frequency-setting components

> Do piezo buzzers generate a back-EMF (do I need a diode for
> protection) ?

A driven one shouldn't need a protection diode. Although I have
seen them (a la diode across a relay) in schematics, but that may
be due to the particular sounder. The 12V you apply is simply the
power supply for the driver. Internally the element may be being
driven by 30VAC derived from this 12VDC

> Are piezo-buzzers only for higher (audio-)frequencies ? Or can
> they be made to emit lower freqs ?

They can. You would have to look at the frequency response to
guesstimate what kind of volume you could expect. I made a
referee's whistle from two identical piezos. One piezo was driven
very slightly different in frequency to the other and the resulting
beat tone created a quite realistic fascimile of a pea whistle

> Are they basically single-freq resonators ?

Not exactly. They have a resonant frequency, which is very
apparent in volume when the driver and element are working
together at that frequency, but they will produce notes across a
fairly wide range (think Jingle Bells Christmas cards)

> Can I drive piezo buzzers straight from PIC pins? No resistor ?

Piezo elements are very capacitive and I don't think a single
PIC pin has the cojones to drive them directly, for example with
PWM. There was a discussion about this last year (so it'll be in
the archives). Probably the best bet would be to use a low-side
switch like a FET or bipolar. A bare element, like the ones you
find in birthday cards, will resonate better with one or two
additional components (resistor / inductor)

There are a few design guides for piezos, like this one

http://www.murata.com/catalog/p15e6.pdf

2005\09\08@042732 by Michael Rigby-Jones

picon face


>-----Original Message-----
>From: spam_OUTpiclist-bouncesTakeThisOuTspammit.edu [.....piclist-bouncesKILLspamspam@spam@mit.edu]
>Sent: 08 September 2005 02:49
>To: Microcontroller discussion list - Public.
>Subject: Re:[EE] Piezo buzzers
>
>
>> Can I drive piezo buzzers straight from PIC pins? No resistor ?
>
>Piezo elements are very capacitive and I don't think a single
>PIC pin has the cojones to drive them directly, for example
>with PWM.

I have tried this quite recently, and the PIC has enough grunt to get reasonable volume, better if you can use two PIC pins and drive them in anti-phase to double the voltage swing.

What really makes a huge difference to piezo sounders volume is mountning them in a resonant cavity, i.e. like the plastic encapsulated PCB mounted piezo elements you can get.

Regards

Mike

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2005\09\08@044414 by Jinx

face picon face
> I have tried this quite recently, and the PIC has enough grunt to get
> reasonable volume, better if you can use two PIC pins and drive
> them in anti-phase to double the voltage swing

Ah yes, you've reminded me of some of the previous thread. I think
there was some mention of a vibrated piezo putting voltage back
into the PIC pin

I just got this from the archives, by Dave Van Horn

"Driving a piezo from a micro usually follows a pattern..
One lead grounded, one lead to the micro. Too soft.

Both leads to the micro, driven in opposition. Nice and loud.

Then the strange behaviour begins.

After a while, you notice the similarity in the schematic between
a charge pump voltage doubler and your piezo element and port
pins, and you realize that every time you flip the piezo, you are
flirting with SCR Latchup or glitching your micro.

Then you drive it through a pair of HC inverters at least
and get "happy beeps" "

> What really makes a huge difference to piezo sounders volume
> is mounting them in a resonant cavity, i.e. like the plastic
> encapsulated PCB mounted piezo elements you can get.

That's very true. The volume drops off considerably if the
element is impeded from vibrating freely

2005\09\08@050957 by Vasile Surducan

face picon face
On 9/8/05, Jinx <joecolquittspamKILLspamclear.net.nz> wrote:
> > Two-tone ?
>
> You won't get two-tone sound from a single piezo that has its own driver. That driver is already (probably) optimised for the resonant frequency of the element. You would have to switch one of the frequency-setting components

True, but chopping the buzzer with a (sub) multiple of the resonant
frequency will got two tones for the user ears. The lowest will be
more than a gruff for lower chopping frequence, but would be two
tones.

Vasile

2005\09\08@051314 by Michael Rigby-Jones

picon face


{Quote hidden}

Interesting, I can see the potential issue.  A pair of schottky diodes on each pin would solve this problem.  Driving a Piezo in this manner from any CMOS based IC, such as HC inverters risks the same problem, though latching up your piezo driver is preferable to the micro I guess ;)  

Regards

Mike

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not make any use of this information, or copy or show it to any
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2005\09\08@072208 by Vasile Surducan

face picon face
On 9/8/05, Michael Rigby-Jones <Michael.Rigby-Jonesspamspam_OUTbookham.com> wrote:
{Quote hidden}

Two diodes and two pic pins. At this moment would be much easy for one
inductance in parallel with the piezo and one zenner from the PIC pin
to ground.
One pic pin, nice loud, no problems. Highest loud with the inductance
having median point supply, acting as a high voltage transformer.

cheers,
Vasile

2005\09\08@155641 by Mark Rages

face picon face
On 9/8/05, Michael Rigby-Jones <RemoveMEMichael.Rigby-JonesTakeThisOuTspambookham.com> wrote:
> >After a while, you notice the similarity in the schematic
> >between a charge pump voltage doubler and your piezo element
> >and port pins, and you realize that every time you flip the
> >piezo, you are flirting with SCR Latchup or glitching your micro.
> >
>
> Interesting, I can see the potential issue.  A pair of schottky diodes on each pin would solve this problem.  Driving a Piezo in this manner from any CMOS based IC, such as HC inverters risks the same problem, though latching up your piezo driver is preferable to the micro I guess ;)
>

What if you gave the piezo enough 'dead time' to drain its charge?

E.g. instead of:
10
01
10
01

Use this sequence:
10
00
01
00
10
00
01

where '00' is long enough to let the charge drain out.  (A resistor
across the buzzer might help speed it up).

Regards,
Mark
markrages@gmail
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