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Pulldown resistors and multiple switches

Maybe this is a question for Electronics SE but I’m not a member there yet so hopefully someone will have an answer here.

I did an experiment with having some push-to-make buttons connected to my Uno. I copied the circuit from the aduino.cc website and all worked exactly as expected. Here is my schematic of the circuit as I have it now: Circuit The pins are both held LOW by the Pulldown resistor until the switch is closed, when they go HIGH. All well and good. But I’ve just been looking at the circuit and something puzzles me. I can see a direct connection from Switch 1 to Pin 2 VIA the resistors and the Ground connection – and vice versa, S2 to P1. See my pathway in Red here:

Alt Path Now, to be clear, this is NOT happening – but I just want to understand why not. Is it just that the 2 resistors in combination provide enough resistance to stop the opposite pin from going HIGH? In which case, this Pulldown resistor is actually serving 2 completely different functions in the circuit...?

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True - but (correct me if I'm wrong) the need for the Pulldown resistor shows that even an open circuit actually needs to be grounded to stop the pin from fluctuating - hence the need for the resistor. It seems to me that I would expect more current to flow through 2 resistors than to to flow through an open circuit..?

Lefty
– Lefty

2017年01月31日 18:12:30 +00:00
Commented Jan 31, 2017 at 18:12

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