Longruner Nano ATMega 328P input stays HIGH for 1s longer than the reality

Question

I have a Longruner Nano ATMega 328P (copy of arduino nano, main difference being the USB connector, CH340 instead of the usual FT232, from what I could find using google searches).

I wrote a super basic code to test its signal detection capabilities:

setup(){
  pinMode(13, OUTPUT);
  pinMode(2, INPUT);
}

loop(){
  digitalWrite(13, digitalRead(2));
}

Hard to make it simpler to test a simple thing: when I give a HIGH signal to D2, D13 is HIGH too.

To test it, I used a simple male-male jump cable and connected VIN pin to the D2 one, for a very brief moment. And I notice D13 stays HIGH for around a second (measured with serial, lowest I could get was 996ms after super quickly touching D2 with the jump cable).

I tried to change the pinMode to INPUT_PULLUP following a similar question I found, but it didn't change anything regarding this delay.

Am I doing something wrong? Maybe a wrong configuration? Or is this just a hardware issue due to the fact that I'm using a copy and there's more than just the USb connector that changes?

I can adapt and work with this if it's required, but being able to have an accurate signal detection would help me greatly.

Answer 1

Don't use Vin as a logic source. Use the +5V pin.

Also, disconnecting the pin is not the same as grounding it. It is "floating". For a proper test, connect a +5V to the pin, and follow it with a Gnd.

A floating pin has an undefined logic level.

What would work in your case is to have a (say) 1k resistor between D2 and Gnd. That way, the moment you disconnect the voltage input the "pull-down" resistor will return it to 0V.