Using arduino digital PIN 0

Hello! I’m newbie in this world. I met arduino a week ago.
Some people including me are having problem with using PIN 0 as a INPUT.
I have a ARDUINO UNO R3.
As specification, PIN 0 and 1 are can be used as INPUT and OUTPUT if you are not using serial functions. But many times it does not work. I tried, but can’t find information about it.
I tested PIN 0 as a push switch and found it works well with pull up switch.
But PIN 0 always stays HIGH with pull down switch.
Many people use 10K resistors for switch. But PIN 0 does not work with pull down switch using 10K resistor. And if you make pull down switch with resistors with resistors lower than 10K, it works on PIN 0. ( I used 5K resistor)

]:slight_smile: So I think that some circuits in aduino make PIN 0 has higher voltage.
:fearful: I’m not good at electronics, so not sure it is safe for my arduino. :fearful: IS THAT OK?

Pin 0/1 is uses when u upload programs, so nothing should be connectet... (upload problems)
Your program should not contain "serial.begin"-statment

Yes. Leaving PIN 0 and 1 is better idea.

Unless they can be used, it may causes further problems.

Keep the USB disconnected while those pin are used

There is a 1K resistor connected to the serial driver hardware on these pins so any circuitry has to overcome that. That means the normal 10K pull values will not work. You have to go much lower like 330R.

Thanks for help
Actually, the resistor i used was not 5K. I guess that was about few hundreds, and I don't know exactly.

Any way, the mystery is over. Thanks :slight_smile:

But I would not use PIN 0& 1.