>From: Andrew Kunz <akunzspam_OUTTDIPOWER.COM>
>Reply-To: pic microcontroller discussion list <@spam@PICLISTKILLspamMITVMA.MIT.EDU>
>To: KILLspamPICLISTKILLspamMITVMA.MIT.EDU
>Subject: Re: [EE]: PWM-to-analog voltage
>Date: Tue, 8 Aug 2000 10:38:15 -0400
>
>Thanks, David.  The tech hunted around and found some 1N34's in the stock
>room.
>He's swapping them out now.
>
>Thanks.
>
>Andy
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>David & Lily Covick <RemoveMEdacTakeThisOuTWEST.NET> on 08/08/2000 10:27:08 AM
>
>Please respond to pic microcontroller discussion list
><spamBeGonePICLISTspamBeGoneMITVMA.MIT.EDU>
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>  To:      TakeThisOuTPICLISTEraseMEspam_OUTMITVMA.MIT.EDU
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>  cc:      (bcc: Andrew Kunz/TDI_NOTES)
>
>
>
>  Subject: Re: [EE]: PWM-to-analog voltage
>
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>Andy,
>
>The diodes are very important....you are correct.  If you do not use 1N34's
>or a germanium diode substitute, then it will not work
>properly......believe
>it or not :)
>
>I know the circuit works fine and I've shared it with others with
>success....
>
>Keep on trying.  Possibly it will work with silicon with
>modification.....but the 1N34's are needed for low forward drop....this is
>what is killing the operation.
>
>I think another alternative is a 1N270.....try looking up that one.
>
>David
>
>

> He's swapping them out now.
>
> Thanks.
>
> Andy
>
>
>
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> David & Lily Covick <EraseMEdacWEST.NET> on 08/08/2000 10:27:08 AM
>
> Please respond to pic microcontroller discussion list

>
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>  To:      RemoveMEPICLISTspam_OUTKILLspamMITVMA.MIT.EDU
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>  cc:      (bcc: Andrew Kunz/TDI_NOTES)
>
>
>
>  Subject: Re: [EE]: PWM-to-analog voltage
>
>
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>
>
>
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>
> Andy,
>
> The diodes are very important....you are correct.  If you do not use

> it or not :)
>
> I know the circuit works fine and I've shared it with others with
> success....
>
> Keep on trying.  Possibly it will work with silicon with
> modification.....but the 1N34's are needed for low forward drop....this is
> what is killing the operation.
>
> I think another alternative is a 1N270.....try looking up that one.
>
> David
>
>
> ----- Original Message -----
> From: Andrew Kunz <RemoveMEakunzTakeThisOuTspamTDIPOWER.COM>
> To: <EraseMEPICLISTspamspamBeGoneMITVMA.MIT.EDU>
> Sent: Tuesday, August 08, 2000 7:15 AM
> Subject: Re: [EE]: PWM-to-analog voltage
>
>
> > >I designed this little circuit a few months ago using SPICE.
> > >Just vary the PWM and you are home free.  You don't need any external
> > >negative voltage!!  It produces negative voltage on its own using a
> positive
> > >voltage in a charge pumping type method off the PIC PWM.
> > >
> > >The attached virus free jpg schematic will fill you in.
> >
> > Tried it.  Looking at it with a scope, I see a standard "ac-coupled"
> waveform
> > from the PWM output pin relative to GND.  If I disconnect the diode/cap
> circuit,
> > the waveform has nice square form.
> >
> > I didn't have any 1N34's so we stuck in a 1N4004.  Right now I'm

> out a
> > 1N34 cross to see if it's sensitive to the diode type used.
> >
> > Any ideas?  All the connections appear to be correct, diodes are in
> correctly,
> > etc.
> >
> > Thanks.
> >
> > Andy
> >
> > --
> > http://www.piclist.com hint: The PICList is archived three different
> > ways.  See http://www.piclist.com/#archives for details.
> >
>
> --
> http://www.piclist.com hint: The PICList is archived three different
> ways.  See http://www.piclist.com/#archives for details.
>
> --
> http://www.piclist.com hint: The PICList is archived three different
> ways.  See http://www.piclist.com/#archives for details.
>

> >Hummm.....I have it exactly as the schematic shows...the RC to +5 and it
> >works -3 to +1.
> >
> >Well, new one on me......glad you got it working :)
>
> What frequency were you using?
>
> Andy
>
> --
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