i got an ESP32 WROOM32-OLED with a PH-Probe hooked up to it (PIN39). When i short the probe interfcace to get a PH07 reading (connecting the middle of the probe interface to ground) i get really consistent readings via analogRead(1750). When i connect my probe to the interface (PH9.18 calibration solution) the readings (taken every 50/100 or 500ms) are going up and down periodically (e.g. from 1800 to 2200).
I have no idea whe the voltage reading is alternating. I tried hooking up and Voltmeter to the same pin, which reads a steady voltage.
I already shielded the cables and the probe interface to have as little interference as possible and i got cas on the power line (47uF) and on the sens line (0.1uF).
I would appreciate any help.