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PICList Thread
'pH and parallel ports'
1996\04\12@114629 by Bryan S Highland

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I have two questions. The first is does anyone know of a pH transducer or
has anyone ever seen a pic project that monitored pH levels (within a range
of 6.2 to 7.4)?

The second is I would like to have a pic communicate with the parallel port
of a PC. Sending data to the pic is no problem, but I don't know how to send
data from the pic back to the pc. I'd like to be able to use one of the
printer control lines for the pic to let the computer know it is going to
send data and have both the pic and pc using the bi-directional parallel
port bits d0-d7. Does anyone have any C code that accomplishes something
similar?

Thanks for any help,
Bryan S Highland
spam_OUTbshighlandTakeThisOuTspamfau.campus.mci.net

1996\04\12@120605 by Ben L Wirz

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       Get a copy of Sensors, they frequently have pH transducers
advetisements in their magazine along with every other kind of sensor
under the sun.  The Fax Number is 413-637-4343.  Just request a free
subscription, and they will send you the current copy and a form.

       While you certainly could use the parallel port, I would suggest you
look into using a serial port. PIC and PC code is readily available along
with proven circuits.  Another advantage is you can use a simple Terminal
program for debugging the PIC before you even write any code for the PC.
Just a suggestion, I'm sure the parallel port could be done too.

Ben,
Ben Wirz                Check out My Home Page for Great Deals on Bulk Buy's
                       Nitinol Wire, LMD 18200 H Bridge and 10 Mhz PIC 16C84
.....blw2KILLspamspam@spam@cec.wustl.edu      http://cec.wustl.edu/~blw2/index.html

On Fri, 12 Apr 1996, Bryan S Highland wrote:

{Quote hidden}

1996\04\12@142849 by Todd Peterson

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At 11:46 AM 4/12/96 -0400, you wrote:

>The second is I would like to have a pic communicate with the parallel port
>of a PC. Sending data to the pic is no problem, but I don't know how to send
>data from the pic back to the pc. I'd like to be able to use one of the
>printer control lines for the pic to let the computer know it is going to
>send data and have both the pic and pc using the bi-directional parallel
>port bits d0-d7. Does anyone have any C code that accomplishes something
>similar?
>
>Thanks for any help,
>Bryan S Highland
>.....bshighlandKILLspamspam.....fau.campus.mci.net

If you'll consider the serial port instead of the parallel, you'll probably
find a lot more help available.  ANY PIC, even ones without a UART, can send
& receive serial data rather simply.  Swing by E-LAB's home page at
http://www.netins.net/showcase/elab and click on "PARALLAX" at the bottom.
Their application notes illustrate RS232 communications.

-Todd

===========================================================
*** Developers of the PICPlus(TM) Microcontroller Board ***

Todd Peterson, Computer Engineer   (EraseMEtpetersonspam_OUTspamTakeThisOuTnetins.net)
E-LAB Digital Engineering, Inc.

P.O. Box 246
Lawton, IA 51030-0246
(712) 944-5344

Visit us at: http://www.netins.net/showcase/elab/

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TO: tpetersonspamspam_OUTnetins.net   (include POSTAL mailing address)
===========================================================

1996\04\13@083405 by Muntak Son

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On Fri, 12 Apr 1996, Bryan S Highland wrote:

> I have two questions. The first is does anyone know of a pH transducer or
> has anyone ever seen a pic project that monitored pH levels (within a range
> of 6.2 to 7.4)?
>
> The second is I would like to have a pic communicate with the parallel port
> of a PC. Sending data to the pic is no problem, but I don't know how to send
> data from the pic back to the pc. I'd like to be able to use one of the
> printer control lines for the pic to let the computer know it is going to
> send data and have both the pic and pc using the bi-directional parallel
> port bits d0-d7. Does anyone have any C code that accomplishes something
> similar?
>
> Thanks for any help,
> Bryan S Highland
> @spam@bshighlandKILLspamspamfau.campus.mci.net
>

For pH measurement, you can use a glass electrode that has a reference
electrode inside. Then you must make a high impedance voltage amplifier
using a least ELECTROMETER order op-amp( ultra-low input bias current,
less than 500 femto ampere). OP amp or AD549 can do that. You also need
good sielding and faraday cage to protect the circuit from noise.
 The glass electrode is quite expensive. And the interfacing circuit is
not so easy as you imagine because the PCB should be clean -you have to
wash it with pure water which contain alaytical grade detergent after
soldering. The high impedance pine need teflon support to prevent leakage
current. The other notorious problem is the glass electrode is dependent
on TEMPERATURE. It means you need a temperature sensor. The dependecy is
so significant that you can not ignore it. The temperature-dependancy
is fortunately linear so that you can compensate by using a simple
subroutine on your PIC firmware.
 THAT's why they made pH-ISFET to measure pH.pH-ISFET(ion-sensitive
field effect transister) is a FET which has a pH sensitive membrane over
the gate of FET. Therefore, pH is directly converted to current
(low impedance) without high impedance amplifier. ISFET is much cheaper
than glass electrode. A guy in our lab produce ISFET in large quantity.
The disadvantage of ISFET is also significant. It's not so accurate.
It has drift. It last only for weeks or month.
But it is disposable. You can buy pH ISFET from Cole-Parmer.
 You can download a commnication program with source from SimTel( a FTP site
). A genious made a file transfer software using LPT and it has
everything you want. Actually the INTERLNK in MSDOS 6.2 is basically the
asme as his briliant work.

 I have a circuit diagram of glass electrode and ISFET interface. You
can ask me if you wish.

 Muntak Son
School of Chem. Tech. Univ. of South Australia, Adelaide

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