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Gary Bishop's CO2/PH controller

Hello all,

     I have collected a few parts from Radio Shack and Home Depot, and I am
almost ready to begin construction of this project.  Has anyone else built
thing?  I am unsure of the VCC he's giving the LM339 IC.  I'm assuming it's
either 5 volts or 12, but he didn't include the vcc pin in his schematic.
Also, anyone who has any ideas for improving the hysteresis and response
time of the probe is welcome to comment or e-mail me directly.
Perhaps a very small powerhead or some device to agitate the water in the
tube would help some of the CO2 to escape from the tank and cause a faster
color change in the reagent-filled bottle.  Or maybe a small 12 v CPU fan
help.  He also didn't mention how much reagent to add to the 15 ml of water.
I'm guessing I could add 3 drops per 5 ml. (Aquarium Pharmaceuticals PH kit)
     I originally wanted to built Jim Hurley's circuit, but I decided to start
and cheap.  (Hurley's circuit requires a PH probe= $50 that I don't want to
invest just yet)