Post by thread:[EE] Piezo buzzers

> Two-tone ? You won't get two-tone sound from a single piezo that has its own driver. That driver is already (probably) optimised for the resonant frequency of the element. You would have to switch one of the frequency-setting components > Do piezo buzzers generate a back-EMF (do I need a diode for > protection) ? A driven one shouldn't need a protection diode. Although I have seen them (a la diode across a relay) in schematics, but that may be due to the particular sounder. The 12V you apply is simply the power supply for the driver. Internally the element may be being driven by 30VAC derived from this 12VDC > Are piezo-buzzers only for higher (audio-)frequencies ? Or can > they be made to emit lower freqs ? They can. You would have to look at the frequency response to guesstimate what kind of volume you could expect. I made a referee's whistle from two identical piezos. One piezo was driven very slightly different in frequency to the other and the resulting beat tone created a quite realistic fascimile of a pea whistle > Are they basically single-freq resonators ? Not exactly. They have a resonant frequency, which is very apparent in volume when the driver and element are working together at that frequency, but they will produce notes across a fairly wide range (think Jingle Bells Christmas cards) > Can I drive piezo buzzers straight from PIC pins? No resistor ? Piezo elements are very capacitive and I don't think a single PIC pin has the cojones to drive them directly, for example with PWM. There was a discussion about this last year (so it'll be in the archives). Probably the best bet would be to use a low-side switch like a FET or bipolar. A bare element, like the ones you find in birthday cards, will resonate better with one or two additional components (resistor / inductor) There are a few design guides for piezos, like this one http://www.murata.com/catalog/p15e6.pdf

>-----Original Message----- >From: spam_OUTpiclist-bouncesTakeThisOuTmit.edu [.....piclist-bouncesKILLspam@spam@mit.edu] >Sent: 08 September 2005 02:49 >To: Microcontroller discussion list - Public. >Subject: Re:[EE] Piezo buzzers > > >> Can I drive piezo buzzers straight from PIC pins? No resistor ? > >Piezo elements are very capacitive and I don't think a single >PIC pin has the cojones to drive them directly, for example >with PWM. I have tried this quite recently, and the PIC has enough grunt to get reasonable volume, better if you can use two PIC pins and drive them in anti-phase to double the voltage swing. What really makes a huge difference to piezo sounders volume is mountning them in a resonant cavity, i.e. like the plastic encapsulated PCB mounted piezo elements you can get. Regards Mike ======================================================================= This e-mail is intended for the person it is addressed to only. The information contained in it may be confidential and/or protected by law. If you are not the intended recipient of this message, you must not make any use of this information, or copy or show it to any person. Please contact us immediately to tell us that you have received this e-mail, and return the original to us. Any use, forwarding, printing or copying of this message is strictly prohibited. No part of this message can be considered a request for goods or services. =======================================================================

> I have tried this quite recently, and the PIC has enough grunt to get > reasonable volume, better if you can use two PIC pins and drive > them in anti-phase to double the voltage swing Ah yes, you've reminded me of some of the previous thread. I think there was some mention of a vibrated piezo putting voltage back into the PIC pin I just got this from the archives, by Dave Van Horn "Driving a piezo from a micro usually follows a pattern.. One lead grounded, one lead to the micro. Too soft. Both leads to the micro, driven in opposition. Nice and loud. Then the strange behaviour begins. After a while, you notice the similarity in the schematic between a charge pump voltage doubler and your piezo element and port pins, and you realize that every time you flip the piezo, you are flirting with SCR Latchup or glitching your micro. Then you drive it through a pair of HC inverters at least and get "happy beeps" " > What really makes a huge difference to piezo sounders volume > is mounting them in a resonant cavity, i.e. like the plastic > encapsulated PCB mounted piezo elements you can get. That's very true. The volume drops off considerably if the element is impeded from vibrating freely

On 9/8/05, Jinx <joecolquittKILLspamclear.net.nz> wrote: > > Two-tone ? > > You won't get two-tone sound from a single piezo that has its own driver. That driver is already (probably) optimised for the resonant frequency of the element. You would have to switch one of the frequency-setting components True, but chopping the buzzer with a (sub) multiple of the resonant frequency will got two tones for the user ears. The lowest will be more than a gruff for lower chopping frequence, but would be two tones. Vasile

{Quote hidden}>-----Original Message----- >From: .....piclist-bouncesKILLspam.....mit.edu [EraseMEpiclist-bouncesspam_OUTTakeThisOuTmit.edu] >Sent: 08 September 2005 09:44 >To: Microcontroller discussion list - Public. >Subject: Re: [EE] Piezo buzzers > > >> I have tried this quite recently, and the PIC has enough >grunt to get >> reasonable volume, better if you can use two PIC pins and drive them >> in anti-phase to double the voltage swing > >Ah yes, you've reminded me of some of the previous thread. I >think there was some mention of a vibrated piezo putting >voltage back into the PIC pin > >I just got this from the archives, by Dave Van Horn > >"Driving a piezo from a micro usually follows a pattern.. >One lead grounded, one lead to the micro. Too soft. > >Both leads to the micro, driven in opposition. Nice and loud. > >Then the strange behaviour begins. > >After a while, you notice the similarity in the schematic >between a charge pump voltage doubler and your piezo element >and port pins, and you realize that every time you flip the >piezo, you are flirting with SCR Latchup or glitching your micro. > Interesting, I can see the potential issue. A pair of schottky diodes on each pin would solve this problem. Driving a Piezo in this manner from any CMOS based IC, such as HC inverters risks the same problem, though latching up your piezo driver is preferable to the micro I guess ;) Regards Mike ======================================================================= This e-mail is intended for the person it is addressed to only. The information contained in it may be confidential and/or protected by law. If you are not the intended recipient of this message, you must not make any use of this information, or copy or show it to any person. Please contact us immediately to tell us that you have received this e-mail, and return the original to us. Any use, forwarding, printing or copying of this message is strictly prohibited. No part of this message can be considered a request for goods or services. =======================================================================

On 9/8/05, Michael Rigby-Jones <Michael.Rigby-Jonesspam_OUTbookham.com> wrote: {Quote hidden}> > > >-----Original Message----- > >From: @spam@piclist-bouncesKILLspammit.edu [KILLspampiclist-bouncesKILLspammit.edu] > >Sent: 08 September 2005 09:44 > >To: Microcontroller discussion list - Public. > >Subject: Re: [EE] Piezo buzzers > > > > > >> I have tried this quite recently, and the PIC has enough > >grunt to get > >> reasonable volume, better if you can use two PIC pins and drive them > >> in anti-phase to double the voltage swing > > > >Ah yes, you've reminded me of some of the previous thread. I > >think there was some mention of a vibrated piezo putting > >voltage back into the PIC pin > > > >I just got this from the archives, by Dave Van Horn > > > >"Driving a piezo from a micro usually follows a pattern.. > >One lead grounded, one lead to the micro. Too soft. > > > >Both leads to the micro, driven in opposition. Nice and loud. > > > >Then the strange behaviour begins. > > > >After a while, you notice the similarity in the schematic > >between a charge pump voltage doubler and your piezo element > >and port pins, and you realize that every time you flip the > >piezo, you are flirting with SCR Latchup or glitching your micro. > > > > Interesting, I can see the potential issue. A pair of schottky diodes on each pin would solve this problem. Two diodes and two pic pins. At this moment would be much easy for one inductance in parallel with the piezo and one zenner from the PIC pin to ground. One pic pin, nice loud, no problems. Highest loud with the inductance having median point supply, acting as a high voltage transformer. cheers, Vasile

On 9/8/05, Michael Rigby-Jones <RemoveMEMichael.Rigby-JonesTakeThisOuTbookham.com> wrote: > >After a while, you notice the similarity in the schematic > >between a charge pump voltage doubler and your piezo element > >and port pins, and you realize that every time you flip the > >piezo, you are flirting with SCR Latchup or glitching your micro. > > > > Interesting, I can see the potential issue. A pair of schottky diodes on each pin would solve this problem. Driving a Piezo in this manner from any CMOS based IC, such as HC inverters risks the same problem, though latching up your piezo driver is preferable to the micro I guess ;) > What if you gave the piezo enough 'dead time' to drain its charge? E.g. instead of: 10 01 10 01 Use this sequence: 10 00 01 00 10 00 01 where '00' is long enough to let the charge drain out. (A resistor across the buzzer might help speed it up). Regards, Mark markrages@gmail -- You think that it is a secret, but it never has been one. - fortune cookie