>In Microchip application notes AN529, it show an example of industrial
>clock.
>
>A speaker was wiring to RA0 of PIC16C57. As a typical speaker have an
>impedence of 8-ohm. I am wondering are I/Os of 16C57 could sufficiently
>drive the speaker. Am I missing anything?
>
>Thanks in advance.
>
>WH Tan
>
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> I do it through a 10uF cap.
>
> PIC + ------- +cap- ---------+ speaker - ------- gnd
>
> http://microengineeringlabs.com/resources/pbpmanual/images/speaker.gif
>
>
> >> In Microchip application notes AN529, it show an example of industrial
> >> clock.
> >>
> >> A speaker was wiring to RA0 of PIC16C57. As a typical speaker have an
> >> impedence of 8-ohm. I am wondering are I/Os of 16C57 could sufficiently
> >> drive the speaker. Am I missing anything?
>
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> high for a long time connected to an 8ohm load to ground. TTYL
>
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> > > > If you do drive it straight from the pin it might be a good idea to
> > > > isolate it in some way.  I'm not sure what sort of inductive kickback
> > > > a speaker would generate from a square-wave, but I doubt the PIC
> > > > would like it if it were directly connected.  I'd put a diode in
> > > > parallel with the winding just to be safe.
> > >
> > >         I'd also recommend a cap to ac couple the speaker,
> > don't want the
> > PIC pin
> > > high for a long time connected to an 8ohm load to ground. TTYL
> >
> >
> > 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

>
> 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
> >
>
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> > 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.
>
> Actually the coil (like any coil) tries to maintain the same *current*,
> which (depending on the resistance encountered) might force it to
> 'generate' a large voltage, which might cause death for an unfortuanate
> semiconductor that was trying to be a high resistance.
>
> Wouter van Ooijen
>
> -- -------------------------------------------
> Van Ooijen Technische Informatica: http://www.voti.nl
> consultancy, development, PICmicro products
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> either.
>
> Mike
> >
> > ----- Original Message -----
> > From: "Mike" <spamBeGonemike.fordSTOPspamEraseMEEARTHLINK.NET>
> > To: <KILLspamPICLISTspamBeGoneMITVMA.MIT.EDU>
> > 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

> > 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,

> > >
> > > 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

> > 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

> > >
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> >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" <spamBeGonemike.fordKILLspamEARTHLINK.NET>
> > > To: <.....PICLISTspam_OUTMITVMA.MIT.EDU>
> > > 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" <TakeThisOuTmike.ford.....TakeThisOuTEARTHLINK.NET>
> > >>> To: <TakeThisOuTPICLISTKILLspamspamMITVMA.MIT.EDU>
> > >>> 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
> > >>>>>>
> > >>>>>
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> >
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