piezo buzzer with a sorry-ass data sheet

takao21203

Joined Apr 28, 2012
3,702
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.
theres plenty surface mount chokes.
Also you get increases by

a) proper acoustic mounting
b) parallel resistor (its a capacitor effectively and needs discharge)
c) AC waveform driving
 

takao21203

Joined Apr 28, 2012
3,702
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 .
Ive sold kinds like these they arent buzzers at all, just tiny speakers, exactly built like a speaker internally with a coil and a membrane usually a tiny metal disc. They dont have electronics inside

Im not looking to troll you but how do you read a datasheet spec sheet? When it says nothing about integrated electronics, as well gives a "coil resistance". Just from that, its an ordinary speaker.

Rated frequency is not something it produces or maintains actively.

Id bet 50:1 its a speaker, SMD kind.
 

takao21203

Joined Apr 28, 2012
3,702
this is for instance a piezo buzzer, passive but with 3rd electrode.
Murata has some circuits, some with coil and some without.

The buzzer type speaker is not used for personal alarm, only for indication, they arent very loud.
Piezo discs with suitable acoustic shell can archieve very high intensity.
Manually you couldnt mount the bare discs suitably without detailed knowledge.
So they are on the market in a suitable shell.

Theres also complete piezo alarm modules which make noise on their own

A piezo disc as such is often used as guitar pickup

1) piezo disc with wires, often used as pickup https://www.ebay.com/itm/10pcs-20mm-piezo-pickup-disc-speaker-with-leads-/142731727762
2) piezo disc / speaker with acoustic shell, typically used for intense alarm https://www.ebay.com/itm/2pcs-Murata-piezo-buzzer-3-electrodes-self-driving-/142548518965 also has 3 electrodes, can be worked in self drive mode
3) small and flat encapsulated piezo disc, typically for indication https://www.ebay.com/itm/8pcs-encapsulated-piezo-speaker-/131821550399
4) piezo disc with 3 electrodes for self drive resonant circuit http://www.ebay.com/itm/8pcs-self-driving-piezo-discs-3-electrodes-/131821346182
5) small TDK piezo buzzer (passive though), nobody sells them on ebay https://www.ebay.com/itm/10pcs-TDK-piezo-buzzer-plastic-housing-leads-/141997440644
6) tiny 12mm encapsulated piezo disc with aluminium shell http://www.ebay.com/itm/10pcs-piezo-buzzer-12mm-aluminium-shell-/142001695830 these kinds are typically found in digital cameras for indication

and theres plenty more piezo kinds on the market for sure

Modules with electronics inside typically are quite large + expensive
 
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BobaMosfet

Joined Jul 1, 2009
1,896
Ive sold kinds like these they arent buzzers at all, just tiny speakers, exactly built like a speaker internally with a coil and a membrane usually a tiny metal disc. They dont have electronics inside

Im not looking to troll you but how do you read a datasheet spec sheet? When it says nothing about integrated electronics, as well gives a "coil resistance". Just from that, its an ordinary speaker.

Rated frequency is not something it produces or maintains actively.

Id bet 50:1 its a speaker, SMD kind.
A small correction to this- regarding comparison to speakers (yes & no). they have a pole in the middle and a magnetic ring on the outside, whereas an actual speaker has the magnet as the pole inside the coil. But otherwise, yes, they are really like little speakers.
 

Audioguru

Joined Dec 20, 2007
11,249
A piezo does not need a choke. A piezo is made as an AC 2-wires "speaker" or DC with a built-in transistor oscillator. Sine a piezo and its enclosure resonate then a piezo speaker is fed from a simple squarewave.
 

AlbertHall

Joined Jun 4, 2014
11,594
A piezo does not need a choke. A piezo is made as an AC 2-wires "speaker" or DC with a built-in transistor oscillator. Sine a piezo and its enclosure resonate then a piezo speaker is fed from a simple squarewave.
But adding the inductor gets more voltage, more noise, especially from low supply voltages, like 5V.
upload_2018-3-23_15-20-7.png
 

Audioguru

Joined Dec 20, 2007
11,249
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 .
I am human (the last time I checked) but I am old (72) and have normal-for-my-age high frequency hearing loss. I can barely (-40dB) hear 4kHz without my hearing aids. Low frequencies below 250Hz are fine without the hearing aids.
 

Thread Starter

mikewax

Joined Apr 11, 2016
181
thank you one and all for your time and attention. i've really been struggling with this. the real problem is that i have a small housing to put it in, 6mm.pngand i tried to find one of these:
autoT.png but to no avail. nobody has them. digikey doesn't. mouser, ebay, aliexpress, it's like they don't exist. the only way to get one is to buy one of those keychain siren things and remove it from inside. but when i do, the damn thing is still too big it's 8mm diameter. won't work. i would wind it myself if i only knew how much L it requires. maybe. there's a russian guy who has 2mm ferrite rods (https://www.ebay.com/itm/Ferrite-co...115240?hash=item1ecff762a8:g:-MUAAOSwN2VZVcvg) and i could take the wire from an inductor i already have. and those "tiny 12mm encapsulated piezo disc with aluminium shell" units would probably work well for the transducer.
so i was searching digikey and found these little speaker thingies and it said 90dBA and i thought this will work. now i know how wrong i was.:confused:
there's plenty of websites where they have L calculators and RC calculators. and i have an attiny so i can do that kinda-sorta DAC trick using a PWM channel and a cap. it's just a single frequency.
i appreciate very much all the information you've given me. now i almost know what i'm doing.
 
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Thread Starter

mikewax

Joined Apr 11, 2016
181
b) parallel resistor (its a capacitor effectively and needs discharge)
c) AC waveform driving
thank you for the reply i really appreciate the assistance. my question is, doesn't a square wave produce the largest amplitude since VLpeak = -di/dt?
and is it possible to calculate an optimal value for a bleed resistor? seems to me i'd have to get a pot and just experiment with it.
 

ebp

Joined Feb 8, 2018
2,332
Instead of driving a piezo disk with a square wave on one side and ground on the other, drive it between two CMOS outputs, true and complement, to effectively apply twice the supply voltage. Don't leave it sitting with DC across it. An XOR gate can be used as a controllable inverter to assure DC is not applied when the signal is disabled.
 

Thread Starter

mikewax

Joined Apr 11, 2016
181
Instead of driving a piezo disk with a square wave on one side and ground on the other, drive it between two CMOS outputs, true and complement, to effectively apply twice the supply voltage. Don't leave it sitting with DC across it. An XOR gate can be used as a controllable inverter to assure DC is not applied when the signal is disabled.
hmmm.... a device that can invert VCC and double the voltage? that's an absolute godsend! but how? i don't know about anything like that. i'm using the circuit that AlbertHall showed above (#27). if there's a device that can do this i sure wanna know about it.
 

Audioguru

Joined Dec 20, 2007
11,249
The same as a bridged audio power amplifier. Each wire of the piezo transducer is fed signals but they have opposite phase. A +5V Cmos output on the first wire and the second wire is fed Cmos 0V, then the first wire goes to 0V and the second wire goes to +5V. Then the signal across the piezo is 10V peak-to-peak. The output is 4 times the power of a 5V p-p signal.
 

Thread Starter

mikewax

Joined Apr 11, 2016
181
The same as a bridged audio power amplifier. Each wire of the piezo transducer is fed signals but they have opposite phase. A +5V Cmos output on the first wire and the second wire is fed Cmos 0V, then the first wire goes to 0V and the second wire goes to +5V. Then the signal across the piezo is 10V peak-to-peak. The output is 4 times the power of a 5V p-p signal.
OMG! i wouldn't have ever thought of that! 4 transistors and 2 control lines, and i can double the working voltage. that's awesome :)
hmmmm.... is there a simpler way to commutate the load, like a single device to do that?
 

AlbertHall

Joined Jun 4, 2014
11,594
OMG! i wouldn't have ever thought of that! 4 transistors and 2 control lines, and i can double the working voltage. that's awesome :)
hmmmm.... is there a simpler way to commutate the load, like a single device to do that?
Yep. The inductor scheme also doubles the voltage.
 

Thread Starter

mikewax

Joined Apr 11, 2016
181
Yep. The inductor scheme also doubles the voltage.
yeah i see what you mean. so according to ebp & guru's intructions, i found an h-bridge circuit. i'm wondering if there is an integrated version of it available. maybe some kind of really basic motor driver or something. i'm only driving about 100mA of current. here's the circuit with discreet parts:
mosfet_hb2.png
 

MrChips

Joined Oct 2, 2009
24,609
L298 is most likely the most popular dual H-bridge on eBay. It is a bit overkill for your piezo buzzer as it was meant for driving motors.
 

Audioguru

Joined Dec 20, 2007
11,249
Are you using a high current magnetic buzzer that needs Mosfets to drive its high current, or are you using a low current piezo transducer that uses such a low current that a Cmos Logic IC can drive it? A Cmos logic IC has six inverters in it that can drive it bridged.
 

Thread Starter

mikewax

Joined Apr 11, 2016
181
L298 is most likely the most popular dual H-bridge on eBay. It is a bit over kill for your piezo buzzer as it was meant for driving motors.
yeah that would be too big. i ended up going with the LV8548 from Onsemi. don't have to mess with all those components. now (yipee!) i get to go hunting for a library part for my Eagle schematic.
LV8548.jpg
 

ebp

Joined Feb 8, 2018
2,332
We need a clear statement of intent here. Too man

What is the sound-producing device - piezo or electromagnetic speaker type?
What is the supply voltage?
Is there a specification for the required current at twice the supply voltage?
How is the required square wave to be produced?
What is going to be used to enable sounding (i.e. turn it on and off)?

If the sounder is a small piezo disk type it can be readily driven with twenty five cents worth of common CMOS.
 
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