This is getting rediculous again. Your message contained 1 line of new content and 176 lines of remnants from at least 7 previous messages, including numerous irrelevant "signatures" and 21 lines of completely content free old footers. 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. 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! 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