This uses a transformer isolated DC-DC power converter, and an optical data isolator, to ensure there is no metallic (ohmic) connection between the pH probe and the controller. This isolation eliminates the interference that can be caused by ground loops.
Ok, this is what to do.put a NPN mosfet on the ground line going into the E.C. circuit.You will want to stop all GND from entering the E.C. circuit.When you take your E.C. reading open the NPN mosfet, take your readings then close the mosfet.Your pH will still be a little off.Recalibrate your pH with the E.C. probe in the pH calibration solution (the E.C. probe should be connected to the E.C. circuit and the GND line should be cut off with the PNP mosfet).This has proven to be successful in fixing the pH / E.C. problem.
Put the NPN Mosfet at the ground line coming into the circuit.You know, VCC and GND.Cut the GND line that is powering the circuit not the ground line going to the probe. As far as which mosfet to buy, there are 100's.Here is one that should work well for you: 2N7000_D26Z Turn on the FET when you take an E.C. reading, turn it off when you are done taking readings.
Yes, place the mosfet between the Arduino and the ground line. I am not 100% sure the 2N7000 will work .However, I do believe it will work just fine.It is a quality FET and that's generally all you need. If it were me, I would use it.
So my understanding I have to put this mosfet between the arduino and the Stamp in the ground line but i don't know how to connect it and use the mosfet.
Hi everyone, as promised I am back reporting on what I've done with the results. By the way, I'm not sure why you were told to get a MOSFET involved.. That's not necessary.So, basically what I have done is take the +5VDC and GND from the arduino board to a dc to dc converter. I used a Murata NME0505SC.Then it's quite simple, take two 6N137 optocouplers and wire one to the RX and the other to TX. You'll need to use two resistors for each one, I just used 430R and then you need to put a .01 microfarad cap between pin 5 and 8 for each one per the datasheet. Obviously each of them will be on the separate ground/potentials.Anyway, everything works perfectly now!! Yay! I have my readings stable and accurate with the probe circuit electrically isolated.