I think there are two answers to your question - if the piezo is louder when you drive it with a duty cycle other than 50 % it probably means that the pwm base frequency is not ideal (not the resonance frequency) of the piezo, it would be very coincidential if this happened to be exactly right since ther are not many choices for the base freq. driving it with other than 50% just creates harmonics that are closer to the resonance freq. -the piezo will be damaged (plating corrodes of the piezo) if the dc component of your signal is other than 0 volt. When driving the piezo directly connected from one pin of your pic you will always have a dc component, at 50% duty cycle for a 5 volt pic the dc component would be (50*5 + 50*0 )/100 =2.5 volt the two ways i know to prevent the dc component are (1) driving the piezzo from two different pins of opposite polarity at 50 % duty cycle this would give you a 0 volt dc component (50*10+20*-10)/100=0 volt (2) connecting a capacitor in series with the piezo ( this is ment with the blocking capacitor in the article) this will remove any dc component even without maintaining a 50% duty cycle. Kind regards Peter ----- Original Message ----- From: "Lindy Mayfield" To: Sent: Thursday, June 17, 2004 4:32 AM Subject: Re: [EE]: Piezo buzzer question, how to connect it Thanks Peter. That did help a lot. From this document I have concluded that I need to solder a negative wire on the lower edge on the same side as the red wire. (Instead of on the other side in the middle which is what I tried. It worked ok I guess.) One more question on this please if I may. I found that with the little encased piezo speaker I have that if I feed it a pulse with a 33% duty cycle I get a better sound than if I use 50%. However I read somewhere that you should never use anything other than 50% as anything else may damage the piezo. I find anything about that in this excellent write up below. Has anyone else heard this about the 50%? > > A nice article about these kind of buzzers: > http://www.thedigitalshop.net/techdocs/piezo.pdf > > Manufacturer links catalog with some driver examples and data > for their > piezo's though these have a second wire soldered on the brass > plate: > http://www.murata.com/catalog/p37e18.pdf > http://www.east-mingtao.com/p01_20.htm > > > Hope this helps > > Peter --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.699 / Virus Database: 456 - Release Date: 6/4/2004 -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.