On the Maker.io page about protecting analog inputs with a zener diode, the “connect the zener diode” section is backwards, as zener diodes must be connected in reverse - the anode should be connected to “ground” and the cathode to the input pin. Here is the link and the incorrect info:
"2. Connect the Zener Diode:
- Connect the anode of the Zener diode to the analog input pin on the MCU or ADC.
- Connect the cathode of the Zener diode to ground (GND)."