I built this pH sensor project on a breadboard and I'm having a big problem. The output on the voltmeter is completely erratic, and I'm pretty sure it's due to RF interference. When I connect the probe (via BNC connector), moving the cable or my hands around or just walking around the room causes the readout on the voltmeter to fluctuate wildly.
How can I fix this? I think I must have to do something about grounding the BNC jack, but I don't know how to proceed. For what it's worth, this is the BNC connector I'm using. The probe is the same one used in the first link and this is how things are setup: