2 tone SMD buzzer?

[doobedoobedo]

I'm looking for a solution for audio feedback to button presses.

Space is constrained on the PCB and where it's mounted so I'm looking for something small that makes a noise, preferably with at least 2 distinctive pitches available. It'll be driven/switched by an MCU running at 3.3V.

What do I need to look for?

[KL27x]

Piezo buzzer? The kind without the built in driver. You can get them in SMD packages, self-contained, in a flat 10x10mm square, or so. Or taller round styles. Or if your project has a thin plastic housing, a bare disc can be adhered to the inside surface of the housing, and connected with jumper wires or even spring contacts on the pcb. The housing will become a speaker.

If you are driving it with MCU, you can have all the pitches you want. You just have to make them yourself.

A 4KHz piezo, for instance, is loudest at 4KHz, but it works just fine in that general range. You can probably go up or down an octave and still get good output. You can not only do two distinct frequencies, you can mix them up by quickly alternating different frequencies to make all manner of distinct multi tone buzzes, chirps, and such. You can alter the frequency to get ascending tweets or descending twerps. Sky's the limit.

If you want it to be louder, use two pins from the MCU on either end of the piezo and drive them in opposition. This effectively doubles the voltage.

[doobedoobedo]

That's great. Thanks

I know I have enough room for that. I've only used the big round things before, the ones you just apply a voltage to and they beep.

So I could drive it with a PWM out and adjust the volume using the duty cycle?

It doesn't need to be particularly loud, It's for feedback on button presses for someone who's blind, so it needs to audible but not intrusive, and adjusting the pitch would be extremely useful too.

[KL27x]

Yes, except the part about duty cycle. Well, I guess that part is right, too, if you are talking about the duty cycle of the duty cycle. I mean, you can give it 4KHz at 50% duty cycle at a 10% duty cycle, lol. It might start to sound strange. Your ear will hear the choppiness. But I suppose you can adjust volume kinda sorta like that. Doing things like this gives all sorts of interesting and useful sounds for feedback. You can also adjust the volume by decreasing/increasing tone out of the optimum range, or sticking tape over the top of a self-housed unit.

Strictly changing the duty cycle of your primary wave form input isn't going to affect volume. The piezo disc bends with change in voltage. It doesn't care about static voltage. Ground or 3V, it doesn't matter. The proper way to adjust the volume is by adjusting the peak to peak voltage of your square/sine wave, causing it to flex more or less.

[doobedoobedo]

Got you, so the way to go on volume would be to skip every n^th pulse which should be fairly trivial. I suppose I could always pulse across a diode if it's really loud, the PCB is bound to act as a bit of a sound board.

I'll grab a couple and have a play

[KL27x]

Got you, so the way to go on volume would be to skip every nth pulse which should be fairly trivial.

Again, not exactly. It might work fine in practice, but you would be changing the characteristic of the sound you get. Voltage control would be the "proper way."

I suppose I could always pulse across a diode if it's really loud.,

Yes, dropping some voltage with a series diode or clamping the voltage across the terminals with a diode would certainly attenuate the volume. If you are content to switch just one side, you could use say two pins of a micro, one direct, and one with a diode, to have two volume levels with digital control. You might need to experiment with the value of the pulldown resistor.

the PCB is bound to act as a bit of a sound board.

If you are using the solderable version, no. The piezo disc will be adhered to the inside of a plastic housing which acts as the speaker.

Here's a couple of alert-size/volume piezo transducers I have used.

This is  9mm x 9mm square
http://www.mouser.com/ProductDetail/Murata/PKMCS0909E4000-R1/?qs=%2fha2pyFaduj%2f%2f69qatz5C1VH8HWGfJzgMCAlGHRSrp3n6Xuqea67emVLEHcVDq2j

This one is bigger, but it is nice for the exposed solder tabs
http://www.mouser.com/Search/ProductDetail.aspx?R=254-PB119-ROXvirtualkey12800000virtualkey254-PB119-ROX

At 5V p2p, these are not particularly loud or annoying. If too loud, I find it works to just stick some heavy tape over the top of the device. Also, I have learned that oil contamination will seriously reduce the volume, but it's rather permanent.

Here is an example of the Murata element in action. This is driven from one side, only, 5V p2p square wave.
http://vid18.photobucket.com/albums/b103/klee27x/DSC_3088_zpsimjfpgrd.mp4
The piezo element is underneath the little white label with the green "Lx" over it. I added it after-the-fact, super-gluing it and handwiring a little 8 pin micro to drive it.

[doobedoobedo]

Got you, so the way to go on volume would be to skip every nth pulse which should be fairly trivial.

Again, not exactly. It might work fine in practice, but you would be changing the characteristic of the sound you get. Voltage control would be the "proper way."

I suppose I could always pulse across a diode if it's really loud.,

Yes, dropping some voltage with a series diode or clamping the voltage across the terminals with a diode would certainly attenuate the volume. If you are content to switch just one side, you could use say two pins of a micro, one direct, and one with a diode, to have two volume levels with digital control. You might need to experiment with the value of the pulldown resistor.

the PCB is bound to act as a bit of a sound board.

If you are using the solderable version, no. The piezo disc will be adhered to the inside of a plastic housing which acts as the speaker.

Here's a couple of alert-size/volume piezo transducers I have used.

This is  9mm x 9mm square
http://www.mouser.com/ProductDetail/Murata/PKMCS0909E4000-R1/?qs=%2fha2pyFaduj%2f%2f69qatz5C1VH8HWGfJzgMCAlGHRSrp3n6Xuqea67emVLEHcVDq2j

This one is bigger, but it is nice for the exposed solder tabs
http://www.mouser.com/Search/ProductDetail.aspx?R=254-PB119-ROXvirtualkey12800000virtualkey254-PB119-ROX

At 5V p2p, these are not particularly loud or annoying. If too loud, I find it works to just stick some heavy tape over the top of the device. Also, I have learned that oil contamination will seriously reduce the volume, but it's rather permanent.

Here is an example of the Murata element in action. This is driven from one side, only, 5V p2p square wave.
http://vid18.photobucket.com/albums/b103/klee27x/DSC_3088_zpsimjfpgrd.mp4
The piezo element is underneath the little white label with the green "Lx" over it. I added it after-the-fact, super-gluing it and handwiring a little 8 pin micro to drive it.

I get what you mean about pwming another pwm now.

I'm getting short on pins, so I think experimentation is the way to go, the vid at 5V didn't seem overly loud so 3.3V will probably be OK, I'll see, and there is always scope to add a diode.

Thanks again.

[ebclr]

What about sound & vibration

http://www.aliexpress.com/item/IMC-Hot-Cellphone-Mobilephone-Coin-Flat-Two-Leads-Vibrating-Micro-Motor/32634720386.html?spm=2114.30010308.3.46.dPANGa&ws_ab_test=searchweb201556_8,searchweb201602_4_10037_10017_10021_507_10022_10032_10020_401_10018_10019_101,searchweb201603_3&btsid=6bfce842-a98c-4067-943e-9981ab869a00

[doobedoobedo]

Nice idea, but I want to keep it on the PCB.