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Topic: Getting a nice sound from piezo (Read 3425 times) previous topic - next topic

Feddar

I have been trying various things with a piezo buzzer. I am using the attached schematic, and added a pot before the piezo for volume control.  The sound, however, is rather harsh.  Would anyone please let me know how to make a more smooth sound?

Much appreciated.

DVDdoug

Square waves are "harsh" and you may have a non-square rectangle wave which is even more harsh.   And, piezo speakers are basically tweeters so they don't reproduce low frequencies.

If you want to get an idea of what square and sine waves sound like Audacity can generate sine & square waves at the frequency of your choice, that you can play back on your computer speakers or headphones.

Feddar

Thanks, but can I get a more sinewave-like output from the circuit I posted?

CrossRoads

Add low pass filtering, that will round the corners of the wave and reduce the harshness.
http://sim.okawa-denshi.jp/en/CRlowkeisan.htm
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

larryd

From my experience, you will never get a 'nice' sound out of a piezo.
They are made for volume and usually have a narrow band.
Lowering the drive amplitude will help.
Most are designed with resonance in mind.

Filtering for some center frequency may help as mentioned.


.
No technical PMs.
The last thing you did is where you should start looking.

Feddar

#5
Jun 28, 2016, 06:14 pm Last Edit: Jun 28, 2016, 06:27 pm by Feddar
From my experience, you will never get a 'nice' sound out of a piezo.
I tried a speaker, and no change in harshness.

Quote
Lowering the drive amplitude will help.
The volume lowers a bit, then cuts out.  I'm using a 10K pot.

Add low pass filtering, that will round the corners of the wave and reduce the harshness.
http://sim.okawa-denshi.jp/en/CRlowkeisan.htm
I tried it. Not much change.  I was using 1k resistor and 0.1uF cap.  The volume decreased, but not much else.

Any other suggestions?

DVDdoug

#6
Jun 28, 2016, 08:20 pm Last Edit: Jun 28, 2016, 09:36 pm by DVDdoug
You should probably look for a different chip and build a sine wave generator (if that's what you want) instead of trying to "fake it" with a 555...

But first, it wouldn't hurt to play around with Audacity and connect the piezo to your soundcard so you can diagnose your problems and decide where you want to go with this.

Quote
I tried it. Not much change.  I was using 1k resistor and 0.1uF cap.  The volume decreased, but not much else
Did you make a low-pass filter or a high-pass filter?  

Of course, when you filter-out the harmonics you are filtering-out some of the sound so it won't be as loud.   Plus, a simple RC filter is far from perfect...

Those values are probably in the ballpark, but of course it depends on the frequency.  Did you calculate the frequency of the 555 oscillator?  (I didn't.)    

Did you calculate the duty cycle?   (I didn't.)   A square wave has a 50% duty cycle and will sound the "least-harsh" of any rectangle wave.   It's been several years since I used a 555 but from what I recall, it's not easy to get a square wave.    And if you adjust the pot, you're probably adjusting the duty cycle so you no longer have a square wave.   A type-T flip-flop will convert a rectangle wave to a square wave at half the frequency, but if you want a "pure tone" you want a sine  wave.




P.S.
About a million years ago the company I was working for was designing a new product and they wanted a "beep" for feedback when you pushed the buttons on a membrane keyboard.    At first they were trying to get a pleasant sound,  and the joke was that they were trying to get the least-annoying sound.   :D :D

Feddar

I've tried several speakers on the circuit.  Seems to be the circuit, not the piezo.

There are some nice sounding buzzers out there. It doesnt have to be great, just not annoying.

Any suggestions for circuits I could try?  How about using coils?

Grumpy_Mike

Quote
Any suggestions for circuits I could try?
Try googling
Tank oscillator

jurs

I've tried several speakers on the circuit.  Seems to be the circuit, not the piezo.

Any suggestions for circuits I could try
Try creating sound with the Arduino "tone() function!
Try out playing different frequencies and compare!
Although the tone() ifunction is creating square wave output, the sound sounds rather nice with my piezo and magnetic speakers, except with very low fequencies. Frequencies of 440 Hz or above sound clean, especially when used in playing melodies.

What's the frequency of your circuit?
What's the resonance frequency of your piezo speaker?

I think that that square wave output sounds better/cleaner if the output frequency is higher than the speakers resonance frequency.

Feddar

Tank oscillator
Thanks.  Looks good, but rather complicated.  Other than the basic LC circuit, it is way beyond my understanding.  Do you know of a very simple circuit that would work?  I'm trying to keep it as simple as possible.

Try creating sound with the Arduino "tone() function!
I'll give it a try.  The problem if that I have a distant circuit connected by Cat5, and all the wires are being used.  Using the Arduino to generate the tone will require more wires.  I'd prefer to avoid that.

Grumpy_Mike


Feddar

#12
Jun 29, 2016, 07:53 pm Last Edit: Jun 29, 2016, 08:00 pm by Feddar
Try one of these chips
Tone generator chips
Looks good.  But I can't find on Digikey or eBay.  Seems to be only available in the UK, where shipping charges to Canada are prohibitive.  Also, looks like using the smc0608s, my preference, involves quite a circuit anyhow (from the datasheet).

Thanks anyhow.  Any further suggestions?

How about using a small microcontroller like attiny or pic?

Grumpy_Mike

Would have been nice to know your location first.

A micro controller is going to produce the same waveform as your NE555.

I think all that is left is a proper filter. So what frequency are you trying to make sound better?

Feddar

what frequency are you trying to make sound better?
Not sure about that, sorry.  A high pitch beep like an answering machine.

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