Wee buzzer, magnetic or piezo?

OBW0549

Joined Mar 2, 2015
3,545
If you read the data sheet, it's pretty clear: it's magnetic, not piezo. It's got a 50Ω coil and is rated at 1.5 Vp-p at 2048 Hz. Don't expect to find any resistors or capacitors inside; as mentioned by @AlbertHall, the resonant frequency is determined by the physical structure of the device.

Always read the data sheet (Digi-Key provides a link to it).
 

Thread Starter

upand_at_them

Joined May 15, 2010
510
Yes, I did read the datasheet. But with them so often referred to as "piezo", even by vendors, I thought there might be finer details missing.
 

OBW0549

Joined Mar 2, 2015
3,545
Yes, I did read the datasheet. But with them so often referred to as "piezo", even by vendors, I thought there might be finer details missing.
In this case, the DigiKey description was correct; in any case, when/if the distributor's description and the manufacturer's data sheet don't agree, always defer to the data sheet. Vendor descriptions are sometimes incomplete or just plain wrong.
 

Thread Starter

upand_at_them

Joined May 15, 2010
510
I'm confused by the datasheet:

8-25-2020 9-44-15 AM.png

Driving this from a 5V microcontroller I/O pin. It works, but it's unclear to me whether I should be dropping the voltage with, say, a 100ohm resistor.
 

OBW0549

Joined Mar 2, 2015
3,545
I found that confusing, also. It says the Rated Voltage is 1.5 Vp-p, yet the Operating Voltage is 1.0-3.0 Vp-p? Doesn't make sense to me.

In any case I'd say yes, it might be a good idea to drop the 5 volt drive voltage with a resistor, just to avoid overstressing the buzzer and reducing its lifespan.
 

ci139

Joined Jul 11, 2016
1,696
got one such lying around somewhere - may destroy it for "the science purposes" (but it might be a piezo one tough ??)
... found a 39 , 50 , 135 Ω ones -- the tear-down shows the 50Ω piece :
terminals , coil , magnetic ring with the flexible steel membrane with inertial weight at the middle , resonant chamber
.... so it needs a driver (not an electro-mechanical thingy) https://www.cuidevices.com/product-spotlight/piezo-and-magnetic-buzzers
.
IMG_2078_zm.jpg
IMG_2083_zm.jpg
 
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Thread Starter

upand_at_them

Joined May 15, 2010
510
I found a couple more that I had. These apparently are not all the same. I assumed they were. Or at least close. One produces a sound from strict DC. The others require a square wave DC, like the datasheet in post #1.

And ones that I ordered from Tayda (Tayda Electronics - ELECTROMAGNETIC TRANSDUCER 1-2VDC 30MA PCB 2 PINS) don't appear to be well-suited for direct control by a microcontroller. Dropping the current to the spec'd level brings the voltage well below spec. And getting them to operate in the 1-2V range causes the current to be much higher than spec. They do have an exposed PCB on the bottom, so I could bust open one for science.

I think the large diameter ones (like over 1") are the piezo ones. And the small diameter ones (1/2") are magnetic. Perhaps you can't make a good piezo buzzer in the small 1/2" size.
 

Thread Starter

upand_at_them

Joined May 15, 2010
510
Revisiting this.

The buzzer that prompted this thread turns out to not be magnetic, I think. I posted the Digi-Key page of what I thought was a similar item. But this one measures a very high resistance across the terminals. Not a solid fixed value, but across the terminals is around 30megohm in one direction and around 3megohm in the reverse direction. This would make it piezo? How would I determine its operating parameters? It does buzz with straight DC.
 

Thread Starter

upand_at_them

Joined May 15, 2010
510
got one such lying around somewhere - may destroy it for "the science purposes" (but it might be a piezo one tough ??)
... found a 39 , 50 , 135 Ω ones -- the tear-down shows the 50Ω piece :
terminals , coil , magnetic ring with the flexible steel membrane with inertial weight at the middle , resonant chamber
.... so it needs a driver (not an electro-mechanical thingy) https://www.cuidevices.com/product-spotlight/piezo-and-magnetic-buzzers
View attachment 215584
That appears to be a magnetic buzzer. So it operates like a speaker. It would need pulsed DC to make sound.
 

Audioguru again

Joined Oct 21, 2019
1,908
A transducer (speaker) does not need pulsed DC and does not need a squarewave but will work fine with them. A transducer works from AC at the frequency it is designed for or it also works with a sinewave at its design frequency.
A small transducer is loud at a high frequency and a large transducer can be loud at a lower frequency.

A buzzer needs a circuit that makes pulses like old fashioned sparking contacts or a transistor.
 

AlbertHall

Joined Jun 4, 2014
10,388
Revisiting this.

The buzzer that prompted this thread turns out to not be magnetic, I think. I posted the Digi-Key page of what I thought was a similar item. But this one measures a very high resistance across the terminals. Not a solid fixed value, but across the terminals is around 30megohm in one direction and around 3megohm in the reverse direction. This would make it piezo? How would I determine its operating parameters? It does buzz with straight DC.
Then it is probably a piezo disc with active circuitry built in.
 

Thread Starter

upand_at_them

Joined May 15, 2010
510
A transducer (speaker) does not need pulsed DC and does not need a squarewave but will work fine with them. A transducer works from AC at the frequency it is designed for or it also works with a sinewave at its design frequency.
A small transducer is loud at a high frequency and a large transducer can be loud at a lower frequency.

A buzzer needs a circuit that makes pulses like old fashioned sparking contacts or a transistor.
So the images ci139 posted above, being just a coil and a magnet, will work with AC or pulsed DC, but not straight DC. And the buzzer I have, being able to work from straight DC, has an internal oscillator driver, also works with pulsed DC (already tried it) and may also work with AC (?).

So, the cheapo magnetic transducers (just a coil and magnet), since they're just like a speaker, could actually produce crude audio? The item I have wouldn't be able to, since it's a buzzer with an internal driver.
 

Thread Starter

upand_at_them

Joined May 15, 2010
510
Is there a benefit to operating these little magnetic transducers at the specified resonant frequency? If this is just a coil and a magnet, wouldn't it be good for a range of frequencies just like a speaker? Is it more efficient (more power transferred) at resonance? Mine is specified for 2048Hz.
 
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