Volume Control On Piezo

Hi,
I am trying to control the volume of a piezo by PWM, but
not a great deal of success.

I have also tried HPWM, but the same.

Peizo operating freq 4100 hz

PIC 16F628A

Int Osc, CMON = 7 Vol var word
etc done

For Vol=100 to 250 step 10
PWM PortB.3,vol,10
Pause 200
next

For Vol=100 to 250 step 10
HPWM 1,vol,10
Pause 200
next

Both cause a scratchy sound, with a little volume control.

I am trying to eliminate a resistive pot, and use to PB, for up/down.

kind regards

Peter

Hi Peter,
I am thinking Piezo element is a high impeadance device, you are probably feeding it through a small series capacitor, what would happen if you lower the impeadance with a resistor in parallel with the piezo element to help use up some of the power delivered through the capacitor? Then I believe the duty cycle change would have more effect.

You will have more efficiency and volume by using a small choke (coil) across the piezo to better the resonance. Some experimentation with size (micro Henry) is needed but any will show the difference from none...

Bill

edit... play safe and install a series resistor though, say 330 or 470 ohms.