Piezo Buzzers

[silo_xtreme]

Hey All,

How's everyone?

My electrical engineer put a SMT-2240-T piezo buzzer behind a BC817 (transistor I think).  So,  I'm not sure if I need to generate a 4KHz singal to turn it on, or if I need to just set a pin high.,

I'm not having luck with either.

What's the typical code for an ATMEGA for this type of application?  We're using an ATXMEGA .

Mike

[Trumpkin]

Usually you would just have to switch the pin high.
Here is some code to switch PORTD 7 high:

Code: [Select]

PORTD |= (1<<7);Before you would do that though you would need to declare that pin as an output like this:

Code: [Select]

DDRD |= _BV(PD7);

[silo_xtreme]

Hey Trumpkin,

That is what i orginally thougt, but here is what I found:
http://www.pui.com/audioProducts/MovieClips/TechNotes/Glossary.asp?articalID=1


Since my buzzer is actually on PORTC Pin 6 -also as  Pin 21 on an ATXMEGA128A1  my code is this:

Code: [Select]

// Make PC6 an output
    PORTC.DIR = (1 << 6);

// Set that output to high
   PORTC.OUT = (1 << 6);
and I also tried sending a 4Khz signal as well.

[Trumpkin]

Could you post the datasheet of the buzzer?

[silo_xtreme]

of course!
http://www.projectsunlimited.com/audioproducts/movieclips/products/audioDetailPrint.asp?CATEGORY=2&PARTNUMBER=SMT-2240-TW-R&GUID={AD8833AE-80E1-4EB6-8150-FCEE9CFCB839}

which is also
http://parts.digikey.com/1/parts/479-buzzer-piezo-10v-22mm-4-0khz-smd-smt-2240-tw-r.html

Hope this helps!

[Trumpkin]

Try connecting a nine volt battery to the two terminals of the buzzer (directly).

[silo_xtreme]

Hmm ... kinda hard to do when it's SMT part on a PCB. 

[SmAsH]

find the traces and touch probes/wires?

[Trumpkin]

find the traces and touch probes/wires?

yep, that's what I meant.

[silo_xtreme]

Ok All,

Thanks for the help so far.  When I connect it to a 9V battery I hear something that is almost like static.

Definitely not the correct sound.

Does this imply I need to send in a 4KHZ signal - I'm a bit confused because that's a resonate frequency (output??)

[Trumpkin]

The sound of static implies that this is a piezo transducer and not a piezo buzzer. Read a bit about them here http://www.kpsec.freeuk.com/components/other.htm#piezo. So it looks like you need a square wave with a frequency of about 4khz, which is probably what you were doing before lol....

[silo_xtreme]

LOL.  I'm working on it.

[silo_xtreme]

I think that's the problem. my signal is probably no square. 

[chelmi]

The sound of static implies that this is a piezo transducer and not a piezo buzzer. Read a bit about them here http://www.kpsec.freeuk.com/components/other.htm#piezo. So it looks like you need a square wave with a frequency of about 4khz, which is probably what you were doing before lol....

You are right, it's listed as a piezo transducer on mouser: http://ca.mouser.com/Search/ProductDetail.aspx?qs=sGAEpiMZZMuNFJjvCI6tQgUWCBGptnRr%2f1ZaW3omx7A%3d

[silo_xtreme]

Ok.  So logic check me please.

Wouldn't this cause a 4000 Hz square wave?

Code: [Select]

unsigned int cycles = 30;
unsigned int freq = 4000;
PORTC.DIR |= 1<<6; //make PC6 an output
long i;
while (cycles > 0) {
PORTC.OUT |= 1<<6; // buzzer pin high
for(i=0;i<freq;i++);
PORTC.OUT &= !(1<<6); // buzzer pin low
for(i=0;i<freq;i++);
cycles--;
}
if yes, how would I control the duty cycle?

[chelmi]

Ok.  So logic check me please.

Wouldn't this cause a 4000 Hz square wave?

Code: [Select]

unsigned int cycles = 30;
unsigned int freq = 4000;
PORTC.DIR |= 1<<6; //make PC6 an output
long i;
while (cycles > 0) {
PORTC.OUT |= 1<<6; // buzzer pin high
for(i=0;i<freq;i++);
PORTC.OUT &= !(1<<6); // buzzer pin low
for(i=0;i<freq;i++);
cycles--;
}
if yes, how would I control the duty cycle?

I see several issues.

First, to drive the pin low, you need to use a binary not operator (~), not a logical not (!).
Try:

PORTC.OUT &= ~_BV(PC6)

Second, your delay loop is completely wrong
You need to introduce a delay corresponding to the period and the duty cycle you want.
The period is 1/F, that's easy. A complete iteration (HIGH then LOW) must last 1/4000Hz = 250 microseconds.
The duty cycle of a square wave is 50% so you need to drive your pin HIGH for 250*0.5 = 125 microseconds and then drive your pin low for the same duration.

so basically your loop should look like

Code: [Select]

  unsigned int cycles = 20000;           //make noise for 20000 * 250 microseconds = 5 seconds
  PORTC.DIR |= _BV(PC6); //make PC6 an output
  while (cycles > 0) {
    PORTC.OUT |= _BV(PC6); // buzzer pin high
    //wait for 125 micro seconds
    PORTC.OUT &= ~_BV(PC6); // buzzer pin low
    //wait for 125 micro seconds
    cycles--;
  }

The way you introduce delay is up to you. You can use:
- a busy loop (like you did): it depends on the frequency of your MCU.
- a timer: take a look at this page for more information about timers: http://members.shaw.ca/climber/avrtimers.html

Michel.

[silo_xtreme]

hmm... what compiler are you using?   my compiler does not like the PC6 or _BV function.

Either way, when I just changed _BV( PC6) to (1<<6)

and used delay_us(125)  from WinAVR util\delay.h

I didn't get this working.   I'm still working on it and will report back.

[chelmi]

hmm... what compiler are you using?   my compiler does not like the PC6 or _BV function.

Either way, when I just changed _BV( PC6) to (1<<6)

and used delay_us(125)  from WinAVR util\delay.h

I didn't get this working.   I'm still working on it and will report back.

I'm using avr-gcc 4.3.2 and avr-libc 1.6.2

I dont know WinAVR, but I guess there is a initialization function. Did you call it?

Do you have access to an oscilloscope or a multimeter with frequency measure?