help with opto isolation

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?

there is nothing left for me to google. i cant find any isolator that handles more than 200ma. what am i suppose to do?

Opto isolators are not linear (they don't work for analog).

i want to add an ec meter but i can already imagine the ground loop problems im going to encounter.

Isolated or not you probably can't run them both at the same time, so you'll have to power them on one-at-a-time.

i cant find any isolator that handles more than 200ma.

Right. Most opto-isolators are for switching digital signals, not power. What's 200mA for?

DVDdoug:
Opto isolators are not linear (they don't work for analog).
Isolated or not you probably can't run them both at the same time, so you'll have to power them on one-at-a-time.
Right. Most opto-isolators are for switching digital signals, not power. What's 200mA for?

well i came across these and they look promising. right now my ph sensor works if there are absolutely 0 voltage leakage from the pumps inside the water im measuring. but i was thinking of adding the ec meter but im thinking about the ground loop situation. could i use one of those for each sensor and that solve the problem? the sensor supposedly only uses 20 - 40ma

im a little confused about where to place the Isolator. the ph sensors connects to some opamps in that controller board before it plugs into the arduino.

i think the best solution is for the designers to use isolated circuitry. i dont understand why they dont use it in the first place dont make much sense

Hi.

Read more carefully whenever an answer was given.

DVDdoug already told you all you really need to know, but not the way "instructables" usually does it (which is do this and that, and it will work. But don't dare to ask why).

I'll try to help you a bit too:
You need to build a converter.
To what, is told by DVDdoug.

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 :wink: ]

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.