Not sure. >To make matters worse, your reply was put at the top out of context so it's >not even obvious what it was in reply to. Are you "top posters" too dumb >to >see that it makes a message harder to read, or too arrogant to care? > >It is important to provide the context for a reply, but that rarely >requires >duplicating the entire original message. At the least you could trim the >footer automatically added by the PIClist server, of which there were 4 in >your message. There are eight levels of response in your message. Nine now, I guess. Sorry. Colin > > >gtyler wrote: > > Negative direction, ie towards 0V. > > > > > > ----- Original Message ----- > > From: "Mike" > > To: > > Sent: Saturday, November 29, 2003 1:00 PM > > Subject: Re: [PIC]: Driving a speaker? > > > > > >> On 29 Nov 2003 at 9:02, gtyler wrote: > >> > >> > >>> What I mean is if it is an open drain and you connect the diode one > >>> way it will work as intended, but if it is not an open drain then > >>> no matter which way you fit the diode it shorts the output when it > >>> is driving either positive or negative. > >>> > >>> George > >> > >> That would be true if you can show me a PIC that drives negative, If > >> you use the speaker as a pullup, it's just like driving a relay. Use > >> a stinkin' diode. > >> > >> OTOH, think about all the 555 circuits driving speakers. Ever see a > >> 555 tone generator, warbler, whatever? Ever see even a diode on the > >> output of one of those? I don't recall seeing one. Turn up the > >> volume of your stereo until it clips. You're more likely to blow > >> your speakers. > >> > >> If you've been paying attention, I showed that a PIC ain't gonna > >> like drivin' an 8 ohm speaker and I plugged in 32 ohms and that's > >> too much. So start thinking about an output amp like the emitter > >> follower I think someone mentioned. I've seen enough tone generators > >> with square wave outs and no diodes. One that comes to mind is my > >> line finder. It's just a two tone CMOS oscillator and an "inductive > >> amplifier" they call it which is the $20 way of saying LM386 op-amp. > >> No diodes across that speaker, either. > >> > >> Mike > >>> > >>> ----- Original Message ----- > >>> From: "Mike" > >>> To: > >>> Sent: Saturday, November 29, 2003 12:16 AM > >>> Subject: Re: [PIC]: Driving a speaker? > >>> > >>> > >>>> On 28 Nov 2003 at 22:15, gtyler wrote: > >>>> > >>>> > >>>>> This could be true if it is an open drain output, otherwise it > >>>>> does not matter which way the diode is, > >>>> > >>>> Yes it does. It's called a inductive kick-back and it doesn't care > >>>> if its an open-drain or not. It will attempt to sent a > >>>> high-current spike in the other direction. I wouldn't count on the > >>>> pull-up to absorb it all either. > >>>> > >>>> There's a lot of text below and by top posting, it isn't clear who > >>>> or what you're replying to. > >>>> > >>>>> in one direction the diode will short the > >>>>> output, also an isolating capacitor does not solve it either. > >>>> > >>>> The cap is to protect the speaker in the event that the PIC output > >>>> is inadvertently left high. > >>>> > >>>>> While I have > >>>>> seen PICs work like this I doubt if it is good practice.Rather > >>>>> drive a transistor and use that to drive the speaker. > >>>> > >>>> Why would it be bad practice? It only depends on the amount of > >>>> drive required. If the PIC can drive it... as they say, "If it > >>>> ain't broke, don't fix it." > >>>> > >>>> at 5Vp-p into 8 ohms with no cap: > >>>> > >>>> Vrms = 3.53V and P = 1.56 W avg > >>>> > >>>> with cap and assuming a reasonable square wave at the speaker, > >>>> neglecting cap loss: > >>>> > >>>> Vrms = 2.5V and P = 781mW avg. > >>>> > >>>> NOTE: square wave in this context implies 50% DC, any thing else > >>>> is a pulse or rectangular wave except for 0% and 100% DC > >>>> > >>>> Take 781mW (with cap, which is smart, not for the speakers sake in > >>>> this case, but that of the PIC) and you get: > >>>> > >>>> Irms = sqrt(Pave/R) = 312 mA rms > >>>> > >>>> Ip = 441mA > >>>> > >>>> So much for the 8 ohm speaker with no driver transistor. But that > >>>> removes the abiguity of the technical term "doubt" used above. > >>>> Good guess, though ;-) > >>>> > >>>> BRs, > >>>> Mike > >>>>> > >>>>> George > >>>>> > >>>>>>>> You really want to load the pic output with a diode? > >>>>>>>> > >>>>>>>> George > >>>>>>> > >>>>>>> No, and that wasn't suggested. The diode is there to > > prevent > >>> the > >>>>>> inductive > >>>>>>> kickback from hitting the PIC pin. I don't see how you can say > >>>>>>> you are "loading" the PIC pin with the diode, the diode only > >>>>>>> conducts when the speaker is turned off, and then only conducts > >>>>>>> current due to the attempt to change the current flowing > >>>>>>> through the speaker quickly. It is a similar effect to turning > >>>>>>> off a relay. TTYL > >>>>>> > >>>>>> You're both right - depends which way round the diode is. > >>>>>> > >>>>>> Regards > >>>>>> Sergio Masci > >>>>>> > >>>>> > >>>>> -- > >>>>> http://www.piclist.com hint: PICList Posts must start with ONE > >>>>> topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other > > [BUY]:,[AD]: ->Ads > >>>> > >>>> -- > >>>> http://www.piclist.com hint: PICList Posts must start with ONE > >>>> topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other > >>>> [BUY]:,[AD]: ->Ads > >>>> > >>> > >>> -- > >>> http://www.piclist.com hint: The list server can filter out > >>> subtopics (like ads or off topics) for you. See > >>> http://www.piclist.com/#topics > >> > >> -- > >> http://www.piclist.com hint: The list server can filter out subtopics > >> (like ads or off topics) for you. See http://www.piclist.com/#topics > > >***************************************************************** >Embed Inc, embedded system specialists in Littleton Massachusetts >(978) 742-9014, http://www.embedinc.com > >-- >http://www.piclist.com hint: The list server can filter out subtopics >(like ads or off topics) for you. See http://www.piclist.com/#topics _________________________________________________________________ STOP MORE SPAM with the new MSN 8 and get 2 months FREE* http://join.msn.com/?page=dept/bcomm&pgmarket=en-ca&RU=http%3a%2f%2fjoin.msn.com%2f%3fpage%3dmisc%2fspecialoffers%26pgmarket%3den-ca -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics