Jim, Interfacing a pH probe to PIC is not a simple exercise as I have found over the last three months. The best types are the glass refillable type. Most manufacturers have them. The gel filled electrodes are not refillable and have a finite lifespan of about one year. If the fish tank is saline, you will need a special prode. Regardless you will need a special probe for very long life as the junction tends to clog up with protiens (common in the tank). Probes marked as ATC probes have a seperate temperature sensor in them usually Pt100 or Pt1000. To interface with a PIC you will either need a pre-amplified probe or you have to provide a FET input stage as the pH probe has an impedance of about 10^9 Ohms ( yes 1000 MOhms). I can recommend www.omega.com and www.orionres.com . Both have an excellent range with lots! of useful information on selection and interfacing. Stephan ----- Original Message ----- From: Damon Hopkins To: Sent: Tuesday, May 02, 2000 5:29 AM Subject: Re: [OT] Looking for PH sensor (fish tank) > Jim Ruxton wrote: > > > > I was wondering if anyone can recommend a PH sensor that is fairly > > simple to interface with a PIC either through A/D or serial etc. I'm not > > looking for anything too fancy. I want to be able to monitor the PH of > > the water in a fish tank I'll also be measuring temperature so if there > > is something that does both that would be a bonus. > > Thanks for any suggestions. > > Jim > http://www.coleparmer.com > > Be aware that MOST PH probes are not intended for saltwater use I'd > suggest picking up a PH probe from somewhere that sells the PH equipment > for fish tanks such as > http://www.premiumaquatics.com (if that site is down try > http://www.algaeworkers.com/cgi-bin/loadpage.cgi?13828+/volts/probes.html > ) > or one of these > http://www.jensalt.com > http://www.acropora.com > http://www.exoticfish.com > http://www.marinedepot.com > > there are 2 really good all inclusive controllers, the Neptune and the > octopus check them out for more ideas.