On 9/8/05, Michael Rigby-Jones wrote: > > > >-----Original Message----- > >From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.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 -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist