I have a plant-watering system and changed from nails to capacitive sensors.
As long as I connect one sensor to any of my two inputs and a voltage divider at the other all seems to work fine.
Once I connect 2 sensors (Vcc / GND in parallel to both and 2 ADC pins for each signal) the ADC signal seems to drift over time. Sometimes it starts instantly sometimes after a day or 3.
Has anybody used 2 of them at the same time? What is my problem?
I think there is no problem with the sketch I tried 100 things like delay before reading Sensors but without any success.
I got a 100R/100nF lowpass between Sensor and ADC againt interference but I cannot imagine this being part of the problem.
Look at the pictures:
One has normal values at the yellow line while the red one has no sensor but a voltage divider of 2x1k.
The other has 2 Sensors connected and you can clearly see the drift upwards (down to GND normally but I map it so when it gets wetter the vaue gues up instead down)
It’s just a slight drift over time but enough to make the system not water correctly.
I assume the sensors do mess each other up by now. Maybe because interference from one Sens to the other via Vcc?
ADC has no Vref but measures against Vcc but this could not be the reason normally because Vcc is not going up all time it could just have spikes. But this is a general slow drift over time
(btw. the blue and green lines are the calibration levels they should hold.)