Floating Signal at not connected Analog Input - Diode?

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for sure, not connected analog input reads nonsense.


picture 1 shows circuit , long , b connected there no floating signal. if not, analog input measures ~1,2 v instead of 0. nothing new. driving motor signal in case got broken connection critical.

first thought: connect pulldown resistor analog input bad idea, because voltage divider.


picture 2 shows same circuit diode , if , b not connected there no floating?!

my quesiton: why work? mean diode shouldn't have changed anything?!

quote
connect pulldown resistor analog input bad idea, because voltage divider.
not can see. use of pulldowns or pullups usual way solve problem of floating input.


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