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I have been reading a bit about the internal pullup resistor. I know from past projects in school that resistor themselves are fragile (burnt one by accident due to higher current than was made for).

I have two different Arduino models. One by Intel and rest are standard Arduino Uno.

So I was wondering about safely using the internal pullup resistor on the Arduino Uno. Hence my question is about the internal pullup resistor pinmode; How many pin can you connect to it safely and not overload it?

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Each pin has its own, separate, pullup resistor.

I don't believe you can damage it by drawing current from the port, because the pullup resistor is only active when the port is in high impedance (hi-Z, input) mode.

The pullup resistor can be damaged by overvoltage, static discharge, and the like.

The Uno has 20 kOhm pullup resistors according to this tutorial. If you feed it a 0V signal while the Atmega is running at 5V, the current will be a quarter of a milliamp, which is miniscule.

  • The question was pretty much are there only one internal pullup resistor for all pin? If so is there any dangerous of overlord with so many connections. But apparently not if each pin has it's own resistor. – Vyndicu Jun 23 '16 at 15:05
  • Yes, to clarify: They are separate resistors, with approximately the same value (~20 kOhm on the Atmega328/Arduino Uno). – Dampmaskin Jun 23 '16 at 15:07

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