Hay every one, going shear what im up to today, making PH and EC circuit boards for my upcoming controller project. Im using a schematics I found from a group called practical maker, that have some kits available (arduino shield stuff). This is the original schematic for the PH shield Im entering the schematic in to diptrace now, (free PCB design software) Dose anyone know of any other tested and working circuit schematics? Some background on PH sensing: Im shor u all have seen a PH electrode be for (light bulb thing on the end of ur PH meter) when submerged in a solution a reaction takes place similar to what happens in a battery. The probe produces a small voltage (about 0.06 volt per pH unit). pure water should produce a voltage of 0.00v which has a ph of 7.00 more acidic water should produce a positive voltage of 414mV at PH=0 and more [FONT="]alkaline should produce a negative voltage of 414mV at PH = 14[/FONT] [FONT="]I intend on reading the ph on a microprocessor so the voltage value needs to be between 0 and 5 volts (positive)[/FONT] so I am using a amplifier to control the gain and offset of the mV reading. Not to shor how im going to get the -5 volts needed yet, may end up using a transformer just to test with as I dont have some parts on hand.