DAN107

Piezo Elements

  By Michael Simpson

 

I'm not going to get into the deep theory of piezo elements mainly cause I don't think you need it to make use of these little gems.  There are several different categories and types of piezo elements but for the sake of simplicity I will describe a few as follows.

Raw Piezo element

This type is only the raw element.  They consist of a small piezoceramic plate and electrode.  This type is of element is not much use to us as while it can make noise, without an acoustical enclosure it wont be that loud.

Encased Piezo element

This is the type of element that this paper is written for.  It's the Raw piezo element but it is encased in a small enclosure that is designed to resonate at the operational frequencies of the element. 

Encased Piezo buzzer

The last type is the same as the Encased Piezo element but contains circuitry to generate a tone so that only power is needed to drive this device.  There are two disadvantages to this type of Piezo.

• They cost more

• They normally have a fixed frequency

 

Have you ever hooked a piezo element up to a microcontroller and found that the sound it made while pulsing the pins to be very inadequate?  I have.  After some research I found that most piezo elements were to designed to resonate with the acoustical chamber built into the case.

By varying the frequency you can find the frequency or frequencies that a piezo was designed to operate.  The piezo that I'm using resonates at both 2.1KHz and 4KHz.  This allows it to be used to generate two tones which give us a bit more flexibility for getting someone's attention.

 

 

Hookup

I made the hookup as simple as possible and really the only thing you need for this paper is a Dios and a piezo element.

 

Schematic 1

 

This first program is very simple.  We create two functions to generate a couple of tones.   The main routine just cycles back and forth between the two frequencies.

Program 1 download it here

'Piezo Demo
func main()

output 13

loop:
   highbeep 1000
   lowbeep 1000
   goto loop

endfunc

func lowbeep(dur)
  dim x
   for x = 1 to dur
      toggle 13
      pauseus 202
   next
endfunc


func highbeep(dur)
   dim x
   for x = 1 to dur
      toggle 13
      pauseus 76
    next
endfunc
 

 

This next program uses the Dios TONE library to generate a series of tones.   You can watch the Dios cycle through the frequencies.  Use your ears to see what the actual frequencies the Piezo resonates at.

Program 2 download it here

'Piezo Demo
func main()
   dim x
   output 13

   for x = 1000 to 5000 step 100
      print "Freq=",x
      TONE 13,1000,x
   next

endfunc

include \lib\DiosTone.lib

Try placing a piece of tape over the hole and running through the frequencies again.  Put a small pin hole in the tape.  The tape changes the resonating frequency.  You can do various things to change the resonating frequency of the cavity.  I enlarged the hole to a 1/8" and changed the main resonating frequency to 2600 Hz.

 

This program does things a bit different.  We use the built in PWM generator to make a 42Khz tone.  This tone will run in the back ground independent of your software application.   To turn off the tone just set port 13 to input.

Program 3 download it here

'Piezo Demo
func main()
   dim x

   'Set to input to turn tone off
   output 13

   'Sets up a 42KHz tone
   PWMinit(1)
   PWMperiod(148)
   PWM1duty(75)
   PWMcourse(2)

loop:
   print "Do nothing"
   pause 500
   goto loop

endfunc

include \lib\DiosHWPWM.lib

 

Parts List

Piezo Element

 

6 Cell Battery Holder

9v Battery Clip

7805

 

74HC165

 

DiosPro 40 Pin Chip

Dios Workboard Deluxe

 

Easy RS232 Driver  

DiosPro 28 Pin Chip

Dios 32 Pin Carrier (Carrier #1)

 

9 Pin Cable

Breadboard Regulator