@martinnn said in Protection circuit for Analog Pin: How exactly do you suppose this to function? This is what I put into a online simulator. If I change the impedance on the right then I can adjust the trim pot and it changes the working range. [image: 1551398013598-c8ac1f5a-9119-49ea-a614-6e56c948f1a1-image-resized.png] This is a digital input, not an analog one. Re-read what I wrote about input protection. How much current flows into the input? Draw a schematic including the input protection as in the article you are referring to (hint: Figure 6). Do you mean what you wrote when you said to use an input series resistor. Is the circuit above what you meant? EDIT: I have since found out that the impedance will be minimal. It is just the resistance of a short cable. So less than 1 ohm. Also this device will go into deep sleep in which case there will still be the analog but no power to the FiPy. Won't this then apply a voltage to VDD?

@edward-dimmack The data sheet tells: -0.3 - 3.6V as maximum ratings. If teh source impedance is high, it should withstand a little bit more than that. Us a shottky diode (e.g. 1N5711, BAT48) for input protection, which has a lower forward voltage.

@pierrot10 Vref is an internal voltage independent from the supply voltage of the extension board. And it is, like @seb said, just used for correcting the values returned by the API. The default assumption about VRef is 1100 mV. You may also completely ignore it, and just use wm_1.value() to get the raw value; especially since your application does not seem to be a priori linked to any standard physical quantity. You have have to make your interpretation table of the returned values yourself, and it does not matter if that is mV -> humidity or number -> humidity.

My site is in German. The link to the souce in Github is https://github.com/ckuehnel/pycom/blob/master/mqtt.py.