OOPS made a typo in one calculation ----- Original Message ----- From: "Peter van Hoof" To: Sent: Thursday, June 17, 2004 6:31 AM Subject: Re: [EE]: Piezo buzzer question, how to connect it > 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 HAS TO BE (50*10+50*-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. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.