Driving a piezo with the sound function

[Melanie]

There are three kinds of Piezo things that make a noise...

1. Piezo Transducer
2. Piezo Buzzer
3. Piezo Loudspeaker

The first, Piezo Transducer makes a hell of a noise if you hit it at it's RESONANT FREQUENCY (eg 4kHz). The further away from it's preferred comfort zone, the crappier the sound. If you just connect a DC voltage to it, it usually just goes 'click'.

The second is a Piezo Buzzer. You simply connect a DC voltage to it, and it makes a noise... it doesn't need any kind of external drive as it has an oscillator built-in (if you apply external drive you will usually get a horrible mess of a sound).

Finally is the Piezo Speaker... much harder to find (and more expensive) than types 1 or 2. If you need one badly for your PIC, rip apart your friends most expensive prized LCD monitor.

Sounds to me like you've got option 1 - unless it's not a Piezo...

If you have got Option 1, then coupling it with 100nF is more than sufficient... find the correct Resonant Frequency (Datasheet) and it'll fill your world with noise...

[Christopher4187]

Thanks for the reply. As an example, I've got two types. One is a self drive and the other is an external drive but both are piezo buzzers. The part numbers (Digi-key) are 102-1146-ND and 102-1135-ND respectively.

If I understand correctly, I can use a 100nF cap in series with the buzzer and hit the resonant frequency (which appears to be 8, 16 or 20 KHz) and it will be loud? If I read the PBP manual correctly, the highest it will be is 20 Khz, correct?

So, with a 100nF cap, one side of the buzzer connected to ground and with this line of code:

SOUND PORTB.7,[250,10]

This should get my ear drums bleeding? :0)

[Melanie]

I tend to find the Piezo Transducers need a little experimenting to hit it just right... and in typical Melanie fashion I don't use the in-built PBP Commands and tend to roll my own...

Here's what works for me...

	BeepToneHi var Byte		' Variable for Beep High-Period
	BeepToneLo var Byte		' Variable for Beep Low-Period
	BeepLength var Word		' Number of Repitition Cycles to execute


	'
	'	Subroutine Produces Standard Beep for 2 Seconds
	'	-----------------------------------------------
BeepTwoSeconds:
	BeepLength=8800					' For Two Seconds
	Goto BeepRAW
	'
	'	Subroutine Produces Standard Beep for 100mS
	'	-------------------------------------------
BeepShort:
	BeepLength=435					' For 100mS
	Goto BeepRAW
	'
	'	Subroutine Produces Standard Beep for 250mS
	'	-------------------------------------------
Beep:
	BeepLength=1100					' For 250mS
BeepRaw:
	BeepToneHi=111
	BeepToneLo=BeepToneHi-49
	For CounterC=0 to BeepLength
		High Beeper
		PauseUS BeepToneHi
		Low Beeper
		PauseUS BeepToneLo
		Next CounterC
	Return

Let me tell you how sharply the roll-off is for a Piezo... for me BeepTone=111 is just right... 113 or higher gives about 12dB less Sound Output, 109 or lower similarly.

I literally sat there with a Scope and a For-Next Loop giving me a two-second burst of every value from 50 to 200 to finally decide what value was loudest!