If you plan an industrial measurement only metallic electrodes or FET ion
sensitive electrodes may be taken in disscution, else you may play with
any glass electrodes. However you can't interface such electrodes directly
to 16F84. Maybe to 15f85 or 16F86 when will come to the market ( if they
come) or to any pic with AD. But high impedance amplifier ( except for
very expensive ion sensitive FET probe ) is required.
Vasile

On Wed, 7 Feb 2001, Peter May wrote:

> I work for the CSIRO here in Canberra Australia (I am currently of on sick
> leave)and we used to make our own PH Meters. I can supply an email address
> if you wish of the electronics engineer who developed them..
>
> Regards, Peter.
>
> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Fritz Braun
> Sent: Tuesday, 6 February 2001 9:46 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE]: Liquid Acidity Sensor
>
>
> Alejandro:
>
> There are pH probes available for food processing. Also, since your vinegar
> is liquid, a common pH probe ( relatively inexpensive) should do.
>
> Look at www.omega.com
>
>
> Fritz
>
>
> ----- Original Message -----
> From: "Alejandro Fubini" <alex@FUBINI.FREESERVE.CO.UK>
> To: <PICLIST@MITVMA.MIT.EDU>
> Sent: Tuesday, February 06, 2001 7:17 PM
> Subject: Re: [EE]: Liquid Acidity Sensor
>
>
> > I'm trying to test the acidity level in home brewed vinegar and thought
> > maybe this would be a good way to get to grips with programming PIC's. I
> > guess most sensors are not made to be stuck inside food... Oh well, I'll
> > have to think up of something else to build.
> >
> > Thank you for your replies,
> > --Alex
> >
> > -----Original Message-----
> > From: pic microcontroller discussion list
> > [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Gennette, Bruce
> > Sent: Tuesday, February 06, 2001 5:55 PM
> > To: PICLIST@MITVMA.MIT.EDU
> > Subject: Re: [EE]: Liquid Acidity Sensor
> >
> >
> > pH probes are most often used for this.
> > Basically they use a special type of glass that allows the ionic activity
> > (charge carriers) value in a liquid solution (usually water) to pass
> through
> > the wall to an electrode in a standard solution. The leakage between the
> > solutions inside and outside the special glass is measured and displayed
> as
> > an adjusted value between 10^0 and 10^14 (actually 10^0 to 10^7 each side
> of
> > 10^7). Warning - the probes are expensive and easily poisoned (the glass
> has
> > its special properties permanently changed by reaction with a strong
> > chemical).
> >
> > If you are only interested in testing the one type of solution - eg
> chlorine
> > in a swimming pool then you can measure some alternative property that is
> > indicitive of the pH, such as conductivity.
> >
> > You'll find several PIC based conductivity probe projects on the net if
> you
> > search.  These also suffer from probe poisoning, but the probes are cheap
> > and easy to replace.
> >
> > Bye.
> >
> > > -----Original Message-----
> > > From: Alejandro Fubini [SMTP:alex@FUBINI.FREESERVE.CO.UK]
> > > Sent: Wednesday, 7 February 2001 7:28
> > > To:   PICLIST@MITVMA.MIT.EDU
> > > Subject:      [EE]: Liquid Acidity Sensor
> > >
> > > Hello,
> > >
> > > I was wondering if anyone knows of the existence of acidity sensors. I'm
> > > thinking of building a tester for liquid acidity using a PIC 16F84 and
> > > some
> > > sort of sensor, only I've never come accross one. Any suggestions will
> be
> > > much appreciated.
> > >
> > > Thanks
> > > --Alex
> > >
> > > --
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