[g8wayg8r]

Thanks for the advice. It may be that I've got them connected properly but that's doubtful. I'll take another look.

Ok. Here's the scoop. I've checked my wiring and my notes. I started out with the hysteresis on the non-inverting input but it altered the pH reading due to the additional voltage. I changed it to the non-inverting input hoping it would move the set point so that the meter reading would be the same regardless of a high or low state from the LF411. I would work to drive down the pH after a water change but I guess it was ocillating very slowlywhen it reached the set point. Oh well. Maybe I could could invert the output through another op amp and get what I want. That's another day.

The 1K pull-up resistor on the out put of the LM339 gives me almost 12V. I've got a 220ohm reisistor connecting pin 6 of the LF411 and pin 3 of the LM339. I'm using around 500K for the feedback and that gives me about 0.1 volts hysteresis. It doesn't make much sense given the ratio. I've got a decent Fluke meter - not a $10 home utility type - so I'll go with the volts for now.