Hi,

There are many micro circuits for aquarium temperature controllers - one of the more desirable features is the inclusion of a PH probe.

While there are several diy versions on the web, there was always some drawback, either with supply of the part used or its suitablity to aquarium use.

This little unit has been built, tested and used for over 6 months and gives exellent results, using very common, low cost parts.

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Attached Thumbnails

 

Attached Files

PH_Amplifier.pdf (730.2 KB, 1231 views)

 

Great work!

 

Perfect work !
Are there any pcb files in digital form?

 

The original was created with Ares v5.2 - which saves as a .lyt file or a bitmap image, neither of which is allowed within these pages.
If you want either, please PM me with an email address.

 

hi,
You can download PDFCreator [free] from the web, it uses the PRINTER function to call the PDFCreator.
Produces a good pdf.

pdfforge.org

__________________
Eric " Good enough is Perfect "
I will NOT answer PM's requesting technical help, please use the Forum
PIC tutorials: Nigel's www.winpicprog.co.uk/ Bill's: www.blueroomelectronics.com/

 

I was under the impression that PH probe amplifiers require bias current <1pA. Also, JFET input amplifier (LF356) bias current generally doubles every 10 deg C. In addition, according to Analog Devices, the typical probe has a tempco of 3300ppm/deg C. Your circuit doesn't seem to address these issues. Have probes changed since Analog Devices wrote that app note? Are you solving them in software?

Analog Devices: pH Probe Amplifier :: Amplifying :: Functions & Building Blocks

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Ron

 

Seems a little strange, quoting myself.

Richard,c, if you posted this design just to get your ego stroked, I guess that must have worked.

Ignoring questions sometimes makes them go away. I'm not ready to give up yet. I would love to make a pH meter for my hot tub, but I won't use this design until my questions are answered.

__________________
Ron

 

Hi Richard,

Thanks for the excellent writeup, diagrams, etc.

Can you post your PCB layout file so I can try the circuit out?

Thanks in advance.

Scott

 

Hi Scott,

Afraid all the original files lost in a HDD failure

However the pcb layout in the pdf file was produced to print out to the correct scale of 39 x 88 mm . +- 0.25mm