# piezo buzzer with a sorry-ass data sheet

#### mikewax

Joined Apr 11, 2016
181
Hello everyone,
maybe some of you analog experts can help me. i got a data sheet for a (www.cui.com/product/resource/cmt-8530s-smt.pdf) MAGNETIC BUZZER TRANSDUCER, it's just a pz disc and a coil housed in a resonant casing. WTF? LCOIL= ?, CDISC = ?.
It says that the current consumption is 90 mA. that's with a square wave, 50% duty cycle, at 2730Hz. and a voltage of 0 - 3.6
the RCOIL = 16ohms.
but i have to drive it at different voltages and and duty cycles. how to calculate the current for arbitrary V and duty cycle?
i'm assuming it's a standard parallel L and C circuit.
is it possible with so little information?

#### Sensacell

Joined Jun 19, 2012
2,918
Nothing in the data sheet says anything about piezo anything, it's an electromagnetic device.

Think of it as a speaker with an acoustically resonant housing.

#### Dodgydave

Joined Jun 22, 2012
10,088
I think its a transistor circuit or chip inside as it's polarised , with a resonant frequency of 2.7Khz

#### AlbertHall

Joined Jun 4, 2014
11,608
I think its a transistor circuit or chip inside as it's polarised , with a resonant frequency of 2.7Khz
But then presumably, it would just need a DC supply. You wouldn't need to feed it a square wave.

#### Dodgydave

Joined Jun 22, 2012
10,088
But then presumably, it would just need a DC supply. You wouldn't need to feed it a square wave.
I see your point , but the datasheet sheet has it polarised on the case, must be an error!

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#### Alec_t

Joined Sep 17, 2013
12,315
I don't see any polarisation indication on the device or in the datasheet.

#### AlbertHall

Joined Jun 4, 2014
11,608
I don't see any polarisation indication on the device or in the datasheet.
It does have polarity indications on the mechanical part of the datasheet.

#### mikewax

Joined Apr 11, 2016
181
I don't see any polarisation indication on the device or in the datasheet.
holy crap it IS polarized. there's a teeeeny little "+" on the case. for some reason, the flyback doide did not register in my brain. i assumed it was a pz because it has an output of 90 dB. except.......... damn it's not dB it's dBA. what is dBA?
and i don't know what these specs mean. V = 3.6, I = 90mA, R = 13ohms. these #s obviously don't add up. is there a way to find L?

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#### Alec_t

Joined Sep 17, 2013
12,315
It does have polarity indications on the mechanical part of the datasheet.
Oops. So it does. I assumed the print in post #1 was the whole datasheet.

#### BobaMosfet

Joined Jul 1, 2009
1,898
Datasheet is fine. Perhaps you're wanting to use the buzzer in a way other than which it was designed for?

Per the datasheet, it expects a 3-5VDC @ 50% PWM duty cycle input at the expected frequency. You can see what other frequencies deliver, but it's really meant to input at a given (rated) frequency of 2730 in order to generate a specific tone at about 90dBA. 25dBA is equivalent to a person whispering, as I recall.

#### mikewax

Joined Apr 11, 2016
181
Per the datasheet, it expects a 3-5VDC @ 50% PWM duty cycle input at the expected frequency. You can see what other frequencies deliver, but it's really meant to input at a given (rated) frequency of 2730 in order to generate a specific tone at about 90dBA. 25dBA is equivalent to a person whispering, as I recall.
yeah it's becoming clear now. i misread the data sheet to begin with. but it still seems odd to me that they do not have any number for inductance, or at least an IV curve.

#### Audioguru

Joined Dec 20, 2007
11,249
It is not loud, its 90dB is when it is only 10cm away from your ear.

#### mikewax

Joined Apr 11, 2016
181
It is not loud, its 90dB is when it is only 10cm away from your ear.
well i found another one that's 100dBA @ 5V. what if i used two of these and overdrive them at 6V?

#### AlbertHall

Joined Jun 4, 2014
11,608
Pardon?

#### Audioguru

Joined Dec 20, 2007
11,249
4kHz is pretty high and old people without hearing aids (or young people deafened by rock music) might barely hear them.
A distance of only 10cm is almost wearing them on your ears. With any distance then their sound will be faint. They are too small to do it. Why not use a piezo beeper that is much louder and uses much less current.

#### takao21203

Joined Apr 28, 2012
3,702
its just a speaker

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#### mikewax

Joined Apr 11, 2016
181
4kHz is pretty high and old people without hearing aids (or young people deafened by rock music) might barely hear them.
A distance of only 10cm is almost wearing them on your ears. With any distance then their sound will be faint. They are too small to do it. Why not use a piezo beeper that is much louder and uses much less current.
because the device i'm making is really small. 40 x 25 x 6mm. a pz requires a choke to drive it, and i can't find a choke that is small enough to fit. it would have to have D <= 6mm.

#### Dodgydave

Joined Jun 22, 2012
10,088
That's a 4Khz buzzer, you're better using a Frequency of 2.7Khz to 3.7Khz for maximum hearing sensitivity, as that's what human hearing is tuned to.

Most burglar alarms and sirens are tuned to this band for maximum volume .