notsolowki:
can someone help me isolate my ph sensor circuit. i am using this sensor.
i want to add an ec meter but i can already imagine the ground loop problems im going to encounter. my arduino reads this sensor with the analog pin. how can i isolate this sensor?
You say you have an Arduino that reads "the sensor" (I assume that's the pH sensor, right?). So, it sounds like you have the pH sensor arrangement working, and the issue is, you want to add an EC Meter, but you feel they need to be isolated.
How about using a couple of Arduino Pro Mini's ('cuz their cheap and small -- and being small, maybe they would be easier to locate near the sensor output), one per sensor. OR, one Pro Mini and the existing Arduino [whatever works for you ]
Then use one of the Pro Mini's as the master and opto-isolate a serial connection to the other Pro Mini/Uno/???-- or some such arrangement. The master would process both sensor signals and do whatever with them.
The power hook-ups would be something like: The Arduino for the EC Meter would be connected across the same supply lines as the EC Meter. The pH sensor Arduino would be connected to the same supply as the pH sensor. And each sensor would have its own isolated supply [for instance, each would have it's own wall-wart].
Or, what the heck, why not use three Arduinos [am I crazy?!?] And opto-isolate the two sensor Arduinos to the processor Arduino, using plain ol' digital inputs to receive the isolated signals. Maybe the signal could be PWM where the duty-cycle is proportional to the 0-5V pH sensor output -- and presumably something similar for the EC meter.
Or, what the heckity-heck: Use a voltage to frequency converter on the sensors, or a voltage to PWM, or a voltage to pulse position, or some such method of modulating the analog signal, opto-isolate that, and "demodulate" the signal at the existing Arduino -- that way, only one Arduino, that interprets the modulated and isolated "digitized" signals.