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I have an Arduino project (attiny85) with an input pin configured as INPUT_PULLUP.

I've got an another Arduino a few meters far from the first one.

Both input pins are connected together to a button that will send a low signal when pressed.

What happens if the second project has also an input pull-up?

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If both have similar Vdd and shared gnd then no signal current is shared but the switch to gnd will drive each input separately. Use twisted pair for better immunity to stray pulse noise and add C to debounce xx millisecond.

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Then your pulldown will need to be strong enough to sink both pullups. If your pulldown is a direct connection to ground then you should have no strength issues. The distance might be an issue, but testing should tell you whether or not.

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  • \$\begingroup\$ I'm grounding them. Will not have any kind of sum of voltages between the 2 input_pull-up pins? \$\endgroup\$ Oct 17 '17 at 7:05
  • \$\begingroup\$ @SimoneCabrino There can be no "sum voltages" so forget about that. Placing two inputs with pull-up in parallel means you have halved the pull-up resistor to Vcc. That's no big deal. Your setup will just work. \$\endgroup\$ Oct 17 '17 at 7:37
  • \$\begingroup\$ Provided both grounds are connected together, of course. \$\endgroup\$ Oct 17 '17 at 7:38

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