If the originator sends me an e-mail, I will send back a solution. ----- Original Message ----- From: "Colin Constant" To: Sent: Saturday, November 29, 2003 3:50 PM Subject: Re: [PIC]: Driving a speaker? > 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 -- 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